Reason for specific location of a gnat swarm?

Reason for specific location of a gnat swarm?

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While checking on my yard trees, I noticed a tiny swarm of gnats above one small maple that has a metal cup holder stake used to help train the trunk straighter. Approximate swarm size of 20 - 30 gnats and they hovered about 6 inches above the top of the cup holder.

I know there's studies on the phenomena of swarm behavior, and out of curiosity as to what they would do I put my hand a couple inches above the cup holder. The little swarm repeatedly moved straight upwards 3-4 inches then returned to the original spot as soon as I removed my hand. When I raised my hand up towards the swarm they would move higher and higher and also follow my hand back down as I lowered it. No matter how high I raised my hands if I removed it quickly they returned immediately to the original location. I checked back a half hour later and they are still there and acted the same way.

What might be the reason for that specific preferred location of the swarm? I has been cloudy and humid all morning and I wonder if the metal of the cup holder is changing the air temperature or some other quality that far above itself? I did also notice a stronger sweet smell of the clover in that location but do have clover all over the yard. My other trees, including a very similar sized young maple but without any support next to it, have no swarms so the metal cup holder perhaps is a correlating factor?

I tried adding a picture for reference but can't get it to upload.

'Gnat' is the common name for a number of species of tiny flying insects in the Dipterid suborder Nematocera (, including Ceratopogonidae (biting midges), Chironomid midges (non-biting midges) and Simuliidae (blackflies). Like many other Diptera, a lot of these species mate aerially in swarms: the males gather using visual cues to determine swarm location. I'll try to add more detail to this later on why they go for specific locations, but in the meantime here are some papers on mating swarms in some of the groups normally called 'gnats':

General papers on swarming behaviour in Diptera:

  • Downes, J. A. 1969. The swarming and mating flight of Diptera. Annu. Rev. Entomol. 14: 271-298.

Swarming behaviour of the family Ceratopogonidae:

  • Downes, J. A. 1955. Observations on the swarming flight and mating of Culicoides (Diptera: Ceratopogonidae). Trans. R. Entomol. Soc. London 106: 213-236.
  • Campbell, M. M., and Kettle, D. S. 1979. Swarming of Culicoides brevitarsis Kieffer (Diptera: Ceratopogonidae) with reference to markers, swarm size, proximity of cattle, and weather. Australian. J. Zool. 27: 17-30
  • Zimmerman, R. H., Barker, S. J., and Turner, E. C. 1982. Swarming and mating behavior of a natural population of Culicoides variipennis (Diptera: Ceratopogonidae). J. Med. Entomol. 19: 151-156.
  • Blackwell, A., Mordue, A. J., Young, M. R., and Mordue, W. 1992. The swarming behavior of the scottish biting midge, Culicoides impunctatus (Diptera, Ceratopogonidae). Ecol. Entomol. 17: 319-325.

Swarming behaviour of the family Chironomidae:

  • Gibson, N. H. E. 1945. On the mating swarms of certain Chironomidae (Diptera). Trans. R. Entomol. Soc. London 95: 263-294.
  • Oliver, D. R. 1971. Life history of the Chironomidae. Annu. Rev. Entomol. 16: 211-230.
  • Fyodorova, M. V., and Azovsky, A. I. 2003. Interactions between swarming Chironomus annularius (Diptera: Chironomidae) males: role of acoustic behavior. J. Insect Behav. 16: 295-306.

Swarming behaviour of the family Simuliidae:

  • Moorhouse, D. E., and Colbo, M. H. 1973. On the swarming of Austrosimulium pestilens MacKerras and MacKerras (Diptera: Simuliidae). Australian J. Entomol. 12: 127-130
  • Hunter, D. M. 1979 Swarming, mating and resting behaviour of three species of black fly (Diptera: Simuliidae). Australian J. Entomol. 18: 1-6

What are locusts and why do they swarm?

Locust swarms cause complex agricultural, social, international challenges.

Locusts are large grasshoppers that live on almost every continent of the world and are known for their propensity to gather in large, destructive swarms. However, locusts often live for several generations, spanning decades, in the solitary, sedentary style that's characteristic of other species of grasshoppers. It's when locusts come together that their behavior changes.

Locusts are able to sense when their population density begins to increase, said Hojun Song, an entomologist at Texas A&M University. And in response, "they become gregarious, attracted to each other. They eat more [and] develop faster," he said.

But the conditions must be just right for locusts to join forces. Sudden rainfall, for example, could help feed a growing population and cause flooding that corrals locusts together and attract more locusts to join. What starts as a small group can turn into a thrumming swarm of thousands, millions or even billions of locusts. As part of this transformation, locusts may change color, Song said.

Some species of locusts become migratory, flying long distances across borders in search of food. The most devastating, best-known, and most frequently studied example is the desert locust (Schistocerca gregaria).

"Unlike other pests, which are localized, desert locusts can swarm and fly, and an entire region can be wiped out of crops," as the locusts come through and chow down, said Esther Ngumbi, an entomologist at the University of Illinois at Urbana-Champaign who studies agricultural pests and food insecurity. The enormous swarms of desert locusts can be utterly devastating for famers whose livelihoods depend solely on those crops, she said.

Dragonfly Swarms: Static Feeding Swarms

At long last, I am finally getting to the information about static swarms in dragonflies! Apparently posting once a week is a bit ambitious for my current schedule and even my weekend became one giant black hole of work. I’ve had no time to blog! Better cram this post in quick while I have a few free minutes… :)

Before I jump into what’s known to science about static dragonfly swarms, take a moment to ponder the amazing swarm depicted in this image I found online:

Isn’t that glorious?! I can’t be sure that this is a real photo, but based on what others have reported and what I’ve observed myself, this is certainly not outside the realm of possibilities! The people in the photo aren’t enjoying the experience, even though the dragonflies in the swarm were completely harmless. I wish I were in their place! I would run out and stand in the middle of the swarm, soaking up the sound of the dragonfly wings fluttering against one another and the sight of several thousands of my favorite animals flying in a single location. This is what my heaven looks like! (And yes, you read that right: I did just say that my heaven involved massive numbers of flying insects. What can I say? I’m an entomologist!)

Now for the science! If you’ve read any of my swarming series, you know that dragonflies migrate, sometimes in mass migratory swarms, and that migrating dragonflies have patterns of behavior similar to migrating birds. I have also speculated, based on my own observations and those of people who reported swarms to me early this summer, that the non-migratory swarms (what I call static swarms) are feeding swarms. Today, I’m going to go over what’s known about these swarms. Unfortunately, most of this information is either buried in the scientific literature where it’s largely inaccessible to the public or in a $100 dragonfly book that, while truly brilliant, is also largely inaccessible. And let’s face it. Apart from college libraries, only odonatologists (scientists who study dragonflies) and other entomologists are going to shell out that kind of cash for a dragonfly book. For those of you who don’t LOVE DRAGONFLIES SO MUCH that you’re willing to run out and fork over 100 bucks for a book (i.e. you’re normal), I’ll summarize what is known about static swarms here!

First of all, the static swarms are almost always feeding swarms! I’ll go over the reasons why you might see these feeding swarms in a particular area in a moment, but first a few interesting facts. First, this behavior appears to be exclusively anisopteran. This means that the behavior is observed in dragonflies only, not their close relatives the damselflies. This is probably because dragonflies exhibit vastly superior flight compared to damselflies. However, among dragonflies, many species of both perchers and fliers will take part in the swarms and fly for extended periods of time. Both males and females swarm, though males are more commonly observed. Swarms can be made up of several different species, and can even include other organisms, such as the vertebrate birds and bats. If birds or bats are present, they will usually be found just above the dragonflies, feeding on the same insects the dragonflies are eating rather than on the dragonflies themselves. And for those of you who are shocked at the number of dragonflies in the swarms you’ve see, you likely only saw the tip of the iceberg! In one of the only studies looking at the number of individuals swarming within a population, only 16% of the dragonflies in the area participated in the swarm. Just think: if you see 1000 dragonflies in a static swarm, that means that there were likely 6250 total dragonflies nearby!

You’ll most often see dragonfly swarms near dusk or dawn, and it’s thought that the dragonflies can see flying prey (most often mosquitoes or non-biting midges, but also termites, ants, and honey bees) better when the sun is close to the horizon. During these times, you may notices that dragonflies appear very suddenly, fly in circular patterns over a very specific area for some time, and then disappear as quickly as they arrived. This is because the dragonflies are attracted to large groups of prey organisms. Once the prey numbers drop or they become less active (e.g. as it get darker), the dragonflies move on. If the prey return the next day, the dragonflies likely will too. In some particularly productive areas where prey are consistently available, you might even see a swarm form nearly every day for months.

There are several reasons why dragonflies might congregate in one area versus a similar area nearby, but in nearly every case there is an abundance of prey species present in the area containing the swarm. Dragonfly swarms will form where other insects are swarming. Most people have seen a big swarm of gnats at one point. Those swarms are like a dragonfly buffet! The dragonflies will swoop in and out of the fly swarm, picking off flies and eating them on the wing before going back for more. This is likely what happened in August when the dragonflies descended on Milwaukee. Massive numbers of mosquitoes in the area drew dragonflies into the city and large swarms formed where the mosquitoes were congregating. Dragonfly swarms often form when there is a seasonal emergence of ants or termites as well. This was the case in the swarm I witnessed. The ants and termites were emerging out of the grass and the dragonflies were catching and eating them as they emerged.

Dragonflies might also be attracted to objects that attract other insects. If prey insects are consistently attracted to a particular object, dragonflies can learn to associate that object with a good meal. In one study, dragonflies were found over a set of traps intended to attract other insects, feasting on the insects flying in toward the trap. The prey insects eventually stopped coming to the traps, but the dragonflies returned for several more days. In this case, the dragonflies were attracted to the traps and not the insects themselves because they’d learned to associated the traps with an abundance of prey.

Dragonflies might also be observed swarming in areas where a weather front has just passed through. Insects often get trapped in fronts and are pushed along with the winds for some time before being deposited somewhere else. When they finally free themselves from the front, they might find the dragonflies ready! Dragonflies take advantage of these windfalls of prey by forming swarms and eating the insects as they arrive. This sort of feeding also happens during migratory flights. The same fronts that deposit large numbers of prey insects in an area help the dragonflies fly long distances, so prey is readily available when the dragonflies stop to rest and feed.

In wooded areas, many insects will congregate in sunny, open patches. Lots of dragonfly swarms form in small sunny patches to take advantage of the other insects that are attracted to the spaces. The swarms of prey insects will move as the sun changes position, os the dragonflies will move too.

In high winds, insects will congregate in lee areas (areas protected from the wind). Lees promote dragonfly swarming behavior because of the high abundance of insects found in these areas.

Finally, and I think most remarkably, some dragonflies will swarm in areas where insects are being stirred up due to some sort of disturbance. Mowing your lawn? It disturbs the small insects living in your grass and cause them to fly around more than they usually would. The prey draws the dragonflies in and swarms form. Similarly, some dragonflies have learned to follow large, slow moving objects (these could be people, bicycles, cows, cars, etc) because they disturb prey insects as they move and encourage the prey to fly – often into the eager grip of a hungry dragonfly.

So all of this boils down to one simple concept: any time you have an abundance of dragonflies in an area as well as a significant prey population, you are likely to see dragonfly swarms. The behavior is thus fairly common in many different species of dragonflies. That said, the chances of a single person seeing more than one or two swarms in their lifetime in a single area can be quite low. The conditions have to be just right for swarms to occur, perfect for both a large number of prey insects AND a large number of dragonflies to exist in the same area at the same time.

Next time (and I’ll get the post up much more quickly this time), I’m going to discuss some of the references available for identifying dragonflies, both in print and online. In the meantime, keep sending me swarm reports! I am beyond thrilled with the participation in my swarm project, so keep ’em coming!

Have you seen a dragonfly swarm?

I am tracking swarms so I can learn more about this interesting behavior. If you see one, I’d love to hear from you! Please visit my Report a Dragonfly Swarm page to fill out the official report form. It only takes a few minutes!

Want more information?

Visit my dragonfly swarm information page for my entire collection of posts about dragonfly swarms!

Biology and habits

Mature carpenter ant colonies produce male and female winged reproductive ants (Fig. 3). Environmental conditions cause reproductive ants to emerge and swarm. They mate during these swarms (nuptial flights), which may occur over several days or weeks. After the nuptial flight, the males die and the females begin searching for a nesting site.

After establishing the nest, the female lays eggs and cares for the larvae by feeding them with fluids secreted from her body. Under favorable conditions, the larvae grow, pupate, and become adult worker ants in 4 to 8 weeks. After becoming adults, the new generations of workers expand the nest, excavate galleries, and take over the task of providing food for the queen and larvae.

Carpenter ant colonies start out small the first 2 or 3 years, but then grow rapidly. In 4 to 6 years they can contain up to 3,000 or more ants, depending on the species. These ants can also have interconnected satellite colonies.

Older, mature colonies continuously produce winged reproductives to replace those that die. They produce 200 to 400 winged individuals for reproductive flights each year. Winged reproductives usually develop in late summer, spend winter in the nest, and swarm in spring and early summer.

Further away is better for the bees

In most cases, a swarm won’t decide on a new home that is close to the parent apiary. Yes, it does happen occasionally, but moving further away is advantageous to the nascent colony because it reduces competition with the old one.

The new swarm will likely make its first landing very close to where it came from. It will stay there until the scout bees report their findings and the new colony decides among the choices. This is the best time to catch a swarm that originated from your own apiary, but you need to work fast. While some swarms on the run may stay in place for days, others land for only a few minutes.

Placing your swarm traps further away from the parent colonies can sometimes increase your chances of catching your own swarms, but you can’t count on it. Much of their decision will depend on what is available, and that will depend on where you live.

Huge "Swarm" That Lit-Up Radar Was Almost Certainly Caused By The Military, Not Ladybugs

In early June 2019, a buzzworthy headline about an anomalous ladybug swarm swept through the news cycle. According to the story, National Weather Service radar detected a massive bloom originating out of the Mojave Desert before heading south over Southern California. The story went viral on social media before generating headlines around the world in major news outlets. Despite the plethora of coverage, it seems there was actually scant evidence that the ladybug swarm even existed at all. In fact, based on our investigation, the ladybug swarm seems to have been entirely a figment of the media’s creation, based on a single Tweet, which itself was based on a single volunteer weather observer's report of seeing "specks" in the air. When all of the facts of the case are examined closely, the "ladybug swarm" actually appears to likely have been the result of military testing and training in the area, not a super swarm of bugs.

Here's what happened: On June 4, 2019, at roughly 3:35 PM local time in California, a strange bloom began appearing on weather radar across a large swath of the southern part of the state before drifting for hours into the night. The National Weather Service (NWS) office in San Diego reported the bloom on Twitter, and posted an animated image that clearly showed a linear radar bloom heading southward from an area just north of the city of Barstow, before expanding into a more amorphous cloud shape. Also accompanying the NWS’s tweet was the caption “The large echo showing up on SoCal radar this evening is not precipitation, but actually a cloud of ladybugs termed a 'bloom.'" Within hours, news outlets across the world began running headlines about the alleged ladybug swarm.

It's bee season. To avoid getting stung, just stay calm and don't swat

This summer's wetter conditions have created great conditions for flowering plants. Flowers provide sweet nectar and protein-rich pollen, attracting many insects, including bees.

Commercial honey bees are also thriving: the New South Wales population has reportedly bounced back after the drought and bushfires

While you may have seen a lot of bees around lately, there's no reason to be afraid. Most bees are only aggressive when provoked, and some don't sting at all. And some bee-like insects are actually flies.

We are experts on honey bee and other insect behavior. So let's look at which bees to watch out for, and how to avoid being stung this summer.

Is it a bee, or a wanna-bee?

Bees in Australia comprise both introduced and native species.

Invasive bees found in Australia, all of which can sting, include the widespread European honeybees, bumble bees in Tasmania, and Asian honey bees in Queensland.

Australia is also home to about 2,000 native bees, including 11 stingless species.

Stingless bees live in colonies and produce honey. Other native species, such as blue banded bees and leaf cutter bees, are capable of stinging but are rarely aggressive.

Some insects we see around flowers are actually harmless hoverflies. But their yellow and black stripes mean they are often mistaken for bees.

Bees on flowers are usually more interested in the food they're collecting than the people around them. However, if you're concerned about encountering one on your morning walk or in the garden, there are simple ways to mitigate the risk.

Bees sting when they feel threatened. So when you see one, move slowly and keep your distance. If bees fly close to you, avoid sudden movements such as swatting them away.

And wear closed shoes where bees might fly close to the ground, such as around clover or fallen jacaranda flowers.

What if I see a swarm?

In spring and into summer, healthy honeybee colonies may reproduce by dividing into two. One part of the colony stays at the hive and the other goes looking for a new home.

Worker bees and the queen bee leave the hive in a swarm and find a spot to stay temporarily while scout bees find a new home. That's when you might see a swarm on a tree, vehicle or building.

Once scout bees find a new home, they return to the swarm and communicate the location via the "waggle dance". Once a sufficient number of scouts agree on a new nest site, the swarm lifts into the air and flies to its new home.

Don't panic if you encounter a stationary swarm of bees. The bees will sting only if threatened. But keep your distance.

Moving swarms can pose a higher sting risk, and should be avoided. If you encounter one, move a safe distance away, or indoors if possible. When moving away, avoid fast movements or swatting.

Swarms are usually present for a few hours or days before they move to a permanent location. If the bees are in a risky location (for example, near a footpath or other busy areas), call a beekeeper to safely remove them.

Stingless native bees swarm for two reasons: mating and fighting.

Mating swarms involve males congregating outside a hive to mate with the queen. Fighting swarms occur when a colony of stingless bees attempts to invade another colony. They do not usually pose a risk to humans.

Native bees capable of stinging are solitary, so don't swarm. However, male solitary bees are known to group together on branches in the evening.

When a bee sting happens

Death and serious injury from bee stings is rare. But in Australia, bees are responsible for more hospital visits than snakes or spiders. European honeybees are also responsible for more allergic reactions than any other insect.

Only female bees can sting. Honeybees can only sting once, and die shortly after. This is because their stinger is barbed—once it stings something, the bee can't pull the stinger out. Instead the stinger pulls free from the bee's abdomen and the bee dies.

Other species can sting multiple times because their stingers are not barbed.

When a bee's stinger enters your skin, it injects venom from a sac on its abdomen. When this happens, you're likely to experience temporary swelling and redness.

For most people, reactions to bee venom are shortlived. To limit the amount of venom injected by the bee, quickly remove the sting using the edge of your fingernail or credit card.

In some cases, stings can lead to severe allergic reactions, including anaphylaxis. If you think you may have an allergy to bee stings, speak to your doctor.

And seek medical advice if you are stung in the face or neck, if significant swelling occurs or if you develop symptoms such as wheezing, light-headedness or dizziness.

Learning to like bees

Bees and other insects play an important role in our food production, by moving pollen from one plant to another. They do a similar job in your garden, helping flowers and fruits to flourish.

But worldwide, bees and other pollinators face many threats, including climate change, misuse of pesticides and habitat loss. We must do what we can to keep pollinator populations healthy.

So if you're out and about and see a bee, or even a swarm, try not to panic. The bees are probably focused on the job at hand, and not interested in you at all.

This article is republished from The Conversation under a Creative Commons license. Read the original article.


Most members of the subphylum Hexapoda are insects (class Insecta). In fact, more than half of all known organisms are insects. There may be more than 10 million insect species in the world, most of them yet to be identified. It&rsquos clear that insects, and not humans, dominate life on Earth.

Hexapoda. A cricket on green leaf. Can you find the six legs attached to the thorax?

Structure and Function of Insects

Insects range in length from less than a millimeter to about the length of your arm. They can be found in most habitats, but they are mainly terrestrial. Many can fly, so they are also aerial. Like other arthropods, insects have a head, thorax, and abdomen. They have a wide variety of appendages, including six legs attached to the thorax.

Insects have a pair of antennae for &ldquosmelling&rdquo and &ldquotasting&rdquo chemicals. Some insects can also use their antennae to detect sound. Other sensory organs on the head include several simple eyes and a pair of compound eyes. The compound eyes let insects see images. Butterflies and bees can even see in color. For feeding, the head contains one pair of mandibles and two pairs of maxillae. Insects consume a wide range of foods, and their mouthparts have become specialized. Several variations are shown in Figure below.

Mouthpart Specialization in Insects. The mouthparts of insects are adapted for different food sources. How do you think the different mouthparts evolved?

An insect&rsquos abdomen contains most of the internal organs. Like other arthropods, insects have a complete digestive system. They also have an open circulatory system and central nervous system. Like other terrestrial arthropods, they have trachea for breathing air and Malpighian tubules for excretion.

Insect Flight

The main reason that insects have been so successful is their ability to fly. Insects are the only invertebrates that can fly and were the first animals to evolve flight. Flight has important advantages. It&rsquos a guaranteed means of escape from nonflying predators. It also aids in the search for food and mates.

Insects generally have two pairs of wings for flight. Wings are part of the exoskeleton and attached to the thorax. Insect wings show a lot of variation. As you can see in Figure below, butterfly wings are paper-thin, whereas beetle wings are like armor. Not all insect wings work the same way, either. They differ in how the muscles are attached and whether the two pairs of wings work independently or together. Besides flight, wings serve other functions. They may protect the body (beetles), communicate visually with other insects (butterflies), or produce sounds to attract mates (katydids).

Form and Function in Insect Wings. Beetles, butterflies, and katydids all have two pairs of wings that they use for flight. However, the wings are very different because they have other functions as well.

Insect Reproduction

Nearly all insects reproduce sexually. Some can also reproduce asexually. An example of an insect life cycle is shown in Figure below.

Insect Life Cycle. This diagram represents the life cycle of a mosquito. Most insects have a similar life cycle.

When an insect egg hatches, a larva emerges. The larva eats and grows and then enters the pupa stage. The pupa is immobile and may be encased in a cocoon. During the pupa stage, the insect goes through metamorphosis. Tissues and appendages of the larva break down and reorganize into the adult form. How did such an incredible transformation evolve? Metamorphosis is actually very advantageous. It allows functions to be divided between life stages. Each stage can evolve adaptations to suit it for its specific functions without affecting the adaptations of the other stage.

Insect Behavior

Insects are capable of a surprising range of behaviors. Most of their behaviors, such as flying and mating, are instinctive. These are behaviors that don&rsquot need to be learned. They are largely controlled by genes. However, some insect behaviors are learned. For example, ants and bees can learn where food is located and keep going back for more.

Many species of insects have evolved complex social behaviors. They live together in large, organized colonies (see Figure below). This is true of ants, termites, bees, and wasps. Colonies may include millions of individual insects. Colony members divide up the labor of the colony. Different insects are specialized for different jobs. Some reproduce, while others care for the young. Still others get food or defend the nest.

Termite Nest. This cathedral-like structure is the nest of a huge colony of termites in Australia. In fact, it is the world&rsquos largest known termite nest. It towers 7.5 meters (25 feet) above the ground and houses millions of termites.

Living in a large colony requires good communication. Ants communicate with chemicals called pheromones. For example, an ant deposits pheromones on the ground as it returns to the nest from a food source. It is marking the path so other ants can find the food. Honeybees communicate by doing a &ldquowaggle dance.&rdquo

KQED: Ants: The Invisible Majority

Most of us think ants are just pests. But not Brian Fisher. Known as &ldquoThe Ant Guy,&rdquo he's on a mission to show the world just how important and amazing these little creatures are. In the process, he hopes to catalog all of the world's 30,000 ant species before they become casualties of habitat loss.

KQED: Ladybugs: A Population of Millions

Ladybugs, also known as ladybird beetles, have a life cycle of four to six weeks. In one year as many as six generations of ladybird beetles may hatch. In the spring, each adult female lays up to 300 eggs in small clusters on plants where aphids are present. After a week the wingless larvae hatch. Both the ladybird beetle larvae and adults are active predators, eating only aphids, scales, mites and other plant-eating insects. The ladybugs live on the vegetation where their prey is found, which includes roses, oleander, milkweed and broccoli. Adult ladybugs don&rsquot taste very good. A bird careless enough to try to eat one will not swallow it.

By late May to early June, when the larvae have depleted the food supply, the adults migrate to the mountains. There, they eat mainly pollen. The ladybugs gain fat from eating the pollen and this tides them over during their nine-month hibernation. Thousands of adults hibernate overwinter in tight clusters, called aggregates, under fallen leaves and ground litter near streams. In the clear, warmer days of early spring, the ladybugs break up the aggregates and begin several days of mating.

Insects and Humans

Most humans interact with insects every day. Many of these interactions are harmless and often go unnoticed. However, insects cause humans a lot of harm. They spread human diseases. For example, the deadly bubonic plague of the middle ages was spread by fleas. Today, millions of people die each year from malaria, which is spread by mosquitoes. Insects also eat our crops. Sometimes they travel in huge swarms that completely strip the land of all plant material (see Figure below). On the other hand, we depend on insects for the very food we eat. Without insects to pollinate them, flowering plants&mdashincluding many food crops&mdashcould not reproduce.

Locust Swarm. A swarm of locusts in the African country of Mauritania darkens the mid-day sky. The hungry insects will eat virtually all the plants in their path.

KQED: Better Bees: Super Bee and Wild Bee

Honeybees are one of the most well-known insects on the planet. Bees are naturalized on every continent except Antarctica. Honeybees have a highly developed social structure and depend on their community, or colony, for survival, with a colony containing up to 20,000 bees. When bees search plants for nectar, pollen sticks to the fuzzy hairs that cover their hind legs. At the next flower, some of the pollen rubs off and fertilizes that flower. In this way, bees help improve fruit production. Bees pollinate an estimated 130 different varieties of fruit, flowers, nuts and vegetables in the United States alone. Farmers obviously depend on bees to pollinate crops, such as fruit and nuts, but in recent years thousands of bee colonies have disappeared. This could be a devastating issue for farmers. Can anything be done? Meet two Northern California researchers looking for ways to make sure we always have bees to pollinate crops.

Science Friday: The Road Best Traveled: A Tale of Ants, Slime Mold and the New Jersey Turnpike

For most people, getting stuck in a traffic jam on the New Jersey Turnpike is a grueling lesson in futility. However, in this video by Science Friday, Simon Garnier examines our collective behavior and how relatively simple organisms organize themselves so dynamically.

How to Manage Pests

The shore fly (right) has a more robust body and shorter antennae than a fungus gnat (left).

Shiny trails on the soil surface made by fungus gnat larvae.

Fungus gnats are small flies that infest soil, potting mix, other container media, and other sources of organic decomposition. Their larvae primarily feed on fungi and organic matter in soil, but also chew roots and can be a problem in greenhouses, nurseries, potted plants and interior plantscapes. Adult fungus gnats may emerge from houseplants indoors and become a nuisance.


Fungus gnats (Orfelia and Bradysia species), also called darkwinged fungus gnats (Sciaridae), are dark, delicate-looking flies similar in appearance to mosquitoes. Adult fungus gnats have slender legs with segmented antennae that are longer than their head. Their long antennae distinguish them from the more robust shore flies, which are also found in greenhouses, associated with algae and decomposing organic matter, but have short bristle-like antennae. Although a few species are up to 1&frasl2 inch long, fungus gnat adults commonly are about 1&frasl16 to 1&frasl8 inch long. Wings are light gray to clear, and the common Bradysia species have a Y-shaped wing vein.

Because adult fungus gnats are attracted to light, you first might notice these pests flying near windows indoors. However, in comparison with more active species such as the common housefly (Musca domestica), fungus gnats are relatively weak fliers and usually don&rsquot move around much indoors. Fungus gnats often remain near potted plants and run across (or rest on) growing media, foliage, compost, and wet mulch piles.

Females lay tiny eggs in moist organic debris or potting soil. Larvae have a shiny black head and an elongated, whitish-to-clear, legless body. They eat organic mulch, leaf mold, grass clippings, compost, root hairs, and fungi. If conditions are especially moist and fungus gnats are abundant, larvae can leave slime trails on the surface of media that look like trails from small snails or slugs.


Adult fungus gnats don&rsquot damage plants or bite people their presence is primarily considered a nuisance. Larvae, however, when present in large numbers, can damage roots and stunt plant growth, particularly in seedlings and young plants. Significant root damage and even plant death have been observed in interior plantscapes and in houseplants when high populations were associated with moist, organically-rich soil. Thus, a houseplant that is wilting may not indicate a lack of water, but rather root damage by fungus gnat larvae or (more commonly) other causes of unhealthy roots. However, too much or too little water, root decay fungi, and improper soil conditions (e.g., poor drainage, or waterlogging) are much more common causes of wilted plants.

Serious fungus gnat damage is more common in greenhouses, nurseries, and sod farms. Although larvae also feed on plant roots outdoors, they don&rsquot usually cause serious damage.


Fungus gnats develop through four stages&mdashegg, larva (with four larval stages or instars), pupa, and adult. The tiny eggs and oblong pupae occur in damp organic media where females lay eggs and larvae feed. At 75ºF, eggs hatch in about 3 days, the larvae take approximately 10 days to develop into pupae, and about 4 days later the adults emerge. A generation of fungus gnats (from female to female) can be produced in about 17 days depending upon temperature. The warmer it is, the faster they will develop and the more generations will be produced in a year.

Fungus gnats have many overlapping generations each year. Outdoors, they are most common during winter and spring in interior areas of California, when water is more available and cooler temperatures prevail. They can occur during any time of the year in moist coastal regions and indoors.


Most of the fungus gnat&rsquos life is spent as a larva and pupa in organic matter or soil, so the most effective control methods target these immature stages rather than attempting to directly control the mobile, short-lived adults. Physical and cultural management tactics&mdashprimarily the reductions of excess moisture and organic debris&mdashare key to reducing fungus gnat problems. Commercially-available and naturally-occurring biological control agents can also control this pest. Insecticides are considered an important control option in some commercial plant production but generally aren&rsquot recommended for fungus gnat management in and around the home.


Visual inspection for adults usually is adequate for determining whether a problem exists. You will see adults resting on plants, soil, windows, or walls, or you might see them in flight. Besides looking for adults, check plant pots for excessively moist conditions and organic debris where larvae feed. Yellow sticky traps can be used to trap adults. Chunks of raw potato placed in pots with the cut sides down (not the peels) are sometimes used to monitor for larvae.

Water and Soil Management

Because fungus gnats thrive in moist conditions, especially where there is an abundance of decaying vegetation and fungi, avoid overwatering and provide good drainage. Allow the surface of container soil to dry between waterings. Clean up standing water, and eliminate any plumbing or irrigation system leaks. Moist and decomposing grass clippings, compost, organic fertilizers, and mulches are also favorite breeding spots. Avoid using incompletely-composted organic matter in potting media unless it is pasteurized first, because it will often be infested with fungus gnats. Improve the drainage of the potting mix (e.g., increase the proportion of perlite or sand in the mix). Minimize organic debris around buildings and crops. Avoid fertilizing with excessive amounts of manure, blood meal, or similar organic materials. Screen and caulk leaky windows and doors to help prevent pests from coming indoors.

If you have infested plants, don&rsquot move them to new areas where flies can emerge to infest other pots. In some cases you may wish to toss out severely infested plants.

Purchase and use only pasteurized container mix or potting mix. Commercial growers often treat potting soil with heat or steam before using it this will kill flies and the algae and microorganisms they feed on. Home gardeners can solarize soil:

  • Moisten it.
  • Place it in a bag of transparent plastic or black plastic.
  • Make the pile no deeper than about 8 inches.
  • Place the bagged soil on a slightly elevated surface, such as a pallet in a sunny location, for about 4 to 6 weeks.

See the Pest Note: Soil Solarization for details. Store pasteurized potting soil off the ground and in closed containers to prevent it from becoming infested before use.


In home situations where fungus gnat adults are a nuisance, it may be possible to reduce the problem by using sticky traps available at retail nursery and garden centers. Yellow sticky traps can be cut into smaller squares, attached to wooden skewers or sticks and placed in pots to trap adults. Also, raw potato chunks placed in the soil are very attractive to fungus gnat larvae. These may be used not only to check pots for larvae but also to trap them away from plant roots. After a few days in a pot, remove infested chunks, dispose of them, and replace with fresh ones.

Biological Control

Three commercially available biological control agents can be purchased to control fungus gnats in pots or container media (Table 1). These include Steinernema nematodes, Hypoaspis predatory mites, and the biological insecticide Bacillus thuringiensis subspecies israelensis (Bti). Several Bti products (Mosquito Bits, Gnatrol) are readily available in retail nurseries and garden centers, so these products may be the most convenient for home gardeners to use. Bti does not reproduce or persist indoors, so infestations in potting media might require repeated applications at about five-day intervals to provide control. Nematodes and Hypoaspis mites must be mail-ordered and are live and perishable products, requiring immediate application. Nematodes can provide relatively long-term control of fungus gnat larvae, and they can be self-reproducing after several inoculative applications to establish their populations. Steinernema feltiae is more effective against fungus gnats than other commercially available nematode species. Mix Bti or nematodes with water, and apply as a soil drench, or spray onto media using a hand-pump spray bottle or other spray equipment, following label directions.

Several natural enemies help to manage fungus gnat populations in outdoor systems, such as landscapes and gardens, and indoors in greenhouses and conservatories, including the predatory hunter flies, Coenosia spp. These flies catch and consume adult fungus gnats in mid-air, and prey on fungus gnat larvae in soil while developing as larvae themselves. Conserve these and other natural enemies by avoiding broad-spectrum insecticide applications.

Table 1. Commercially Available Biological Pesticides and Natural Enemies for Controlling Fungus Gnat Larvae.
Biological Comments
Bacillus thuringiensis subspecies israelensis (Bti) (Gnatrol) A naturally occurring, spore-forming bacterium produced commercially by fermentation. Bti applied at labeled rates provides temporary control and is toxic only to fly larvae, such as mosquitoes, black flies, and fungus gnats. Repeat applications commonly are needed for long-term control. This Bt is a different subspecies from that applied to foliage to control caterpillars. Bt labeled for caterpillars is not effective against fly larvae.
Hypoaspis (=Geolaelaps or Stratiolaelaps) miles A light-brownish predaceous mite adapted to feeding in the upper layers of moist soil. Preys on fungus gnat larvae and pupae, thrips pupae, springtails, and other tiny invertebrates. Commercial mites commonly are shipped in a shaker-type container used to apply them. Recommended rates in commercial nurseries are about 1/2 to several dozen mites per container or square foot of media. Make applications before pests become abundant. Hypoaspis probably won&rsquot perform very well in individual houseplants and probably isn&rsquot a good choice for use in homes.
Steinernema feltiae This nematode is effective when temperatures are between 60° to 90°F and conditions are moist. You can apply it as a soil drench and to media using conventional spray equipment. Nematodes reproduce and actively search for hosts, so under moist conditions they can provide season-long control after several initial applications to establish populations.
These materials are essentially nontoxic to people and are compatible for application in combination. Bt is available from many well-stocked nurseries and garden supply stores. Predaceous mites, Bti, and nematodes, are commercially available through mail order from special suppliers.

Chemical Control

Insecticides are rarely warranted to control these flies in and around homes. However, if you do apply an insecticide for fungus gnats, consider using Bti or Steinernema feltiae nematodes to control the larvae see the section Biological Control for more information.

If Bti or nematodes aren&rsquot available and high populations are intolerable, pyrethrins or a pyrethroid insecticide may provide temporary, fast-acting control. Spray the surface of potting soil and plant parts where adults typically rest. Do not aerially fog indoors or attempt to spray adult gnats in flight. Be sure the product is labeled for your particular use (e.g., for "house plants") and read and follow the product's directions.

Pyrethrins have low toxicity to people and pets and are the active ingredients in the botanical pyrethrum, which is derived from flowers of certain chrysanthemums. Many products include a petroleum-derived synergist (piperonyl butoxide, or PBO) to increase pyrethrum effectiveness. Pyrethroids (e.g., bifenthrin, permethrin) are synthesized from petroleum to be chemically similar to pyrethrins they often are more effective and persistent but are more toxic to beneficial insects. When using these products on houseplants or interiorscape containers, if possible move plants outdoors for treatment as a precaution, and wait about a day after applying the chemical before bringing them back inside.

For information on managing fungus gnats in commercial flower, nursery or greenhouse operations, see the UC IPM Pest Management Guidelines: Floriculture and Ornamental Nurseries and the book Integrated Pest Management for Floriculture and Nurseries.


Dreistadt, S. H. 2001 Pest Note: Fungus Gnats, Shore Flies, Moth Flies and March Flies. Oakland: Univ. Calif. Div. Agric. Nat. Res. Publ. 7448.


Cloyd, R. A. 2010. Fungus gnat management in greenhouses and nurseries (PDF) . Kansas State University Agricultural Experiment Station and Cooperative Extension Service. Publication MF-2937:

Dreistadt, S. H. rev. 1986. Fungus Gnats and March Flies. Oakland: Univ. Calif. Div. Agric. Nat. Res. Publ. 7051.

Dreistadt, S. H., J. K. Clark, and M. L. Flint. 2001. Integrated Pest Management for Floriculture and Nurseries. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 3402.

Harris, M. A., R. D. Oetting, and W. A. Gardner. 1995. Use of entomopathogenic nematodes and a new monitoring technique for control of fungus gnats, Bradysia coprophila (Dipt.: Sciaridae), in floriculture. Biological Control 5:412-418.

UC IPM Pest Management Guidelines: Floriculture and Ornamental Nurseries. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 3392.

Nielsen, G. R. 1997. Fungus Gnats. Department of Plant and Soil Science, University of Vermont Extension. Publication EL 50:

Stapleton, J.J. C.A. Wilen, and R.H. Molinar. Pest Notes: Soil Solarization. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 7441.

Wright, E. M., and R. J. Chambers. 1994. The biology of the predatory mite Hypoaspis miles (Acari: Laelapidae), a potential biological control agent of Bradysia paupera (Dipt.: Sciaridae). Entomophaga 39:225-235.


Pest Notes: Fungus Gnats

  • J.A. Bethke, UC Cooperative Extension, San Diego Co
  • S. H. Dreistadt, UC Statewide IPM Program, Davis

Produced by University of California Statewide IPM Program

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Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright © 2019 The Regents of the University of California. All rights reserved.

Infrequently Asked Questions: Why do so many bugs hit my windshield?

The world is full of questions we all want answers to but are either too embarrassed, time-crunched or intimidated to actually ask. In the spirit of that shared experience, we've embarked on a journey to answer all of the questions that burn in the minds of Philadelphians — everything from universal curiosities (Why do disposable coffee cups still leak?) to Philly-specific musings (How does one clean the Liberty Bell?).

If you've driven through a rural area, you're painfully familiar with the experience of having your squeaky clean car pelted by a smattering of insects, whose innards suddenly find a new home on your windshield. Curious as to why and under what conditions this tends to happen, we reached out to the Academy of Natural Sciences at Drexel University Entomology Collection Manager Jason Weintraub for an explanation.

In general, why are there so many insects hitting windshields?

The concise answer I would give to someone is it depends on where they are, what time of year it is, exactly where they’re driving relative to habitats of insects that are abundant in that season, insect behavior as it relates to vehicles moving along roads, the shape and aerodynamics of the vehicle they’re driving and the speed they’re driving. Without knowing those factors, it’s hard to answer questions as to why there are bugs on windows.

So let's say we're talking about a wooded part of Bucks County. Is the insect population there any bigger or more diverse than other parts of the country?

It doesn’t necessarily have greater diversity or abundance than compared to a comparable rural area in, say, Michigan where I’m from, or Washington state or Northern California, but what’s more significant, in terms of the numbers and diversity of insects that end up squashed on people’s windshields, is what type of vehicle they're driving, how fast they drive, where they drive and when they drive it there. That bears much more on the question.

Why would the vehicle matter?

What happens with small insects, is if the vehicle isn’t going very fast, they get caught in the laminar airflow over the surface of the vehicle — especially if it’s an aerodynamic vehicle and they don’t end up impacting the windscreen. They fly over the top of the vehicle. Whereas if it’s a Greyhound bus with a flat front, everything that hits it gets squashed. So the physics of airflow around vehicles, the flight patterns and behavior of the flying insects likely to get hit, are likely to influence how many insects hit the windshield.

The other thing that's important is whether the vehicle is driving through an area where there’s insect aggregation for some reason. So you have aquatic species like mayflies that are very short-lived — they may only be flying for two or three days in one given mayfly population, near a stream or river, and if a car is driving at a high speed during that one-, two- or three -day emergence, over a place where they are having their annual mass emergence to reproduce when the adults are all around looking for mates, then one vehicle crossing one bridge at one point in time may have thousands upon thousands of mayfly bodies impacting on its front end as it speeds across a bridge.

What other factors influence when or how many bugs you're hitting?

The smallest flying insects are not going to hit a windshield if they are impacted by the laminar airflow on a car only going 30 miles per hour, as opposed to 60 miles per hour. They might, however, hit the grill of the car below the windshield. So, it depends on how high above the ground they tend to fly. Most flying insects tend to fly anywhere from two to five feet above the ground. That tends to be in the path of automobiles as they cross roads.

There are other factors, such as whether the car is driving with the headlights on and whether it’s a moonless night or a night with heavy overcast and cloud cover. Nocturnal insects use moonlight to navigate, to keep flight paths going in one direction. They maintain flight path in a specific angle to the moon. When there is no moon, on the night of a new moon, or if the moon is invisible because of dense cloud coverage, they get disoriented because of artificial light sources — and that includes headlights of oncoming vehicles. And many nocturnal insects get attracted to porch lights at your home, but they also get attracted to lights of oncoming cars, and when that happens they’re much more likely to fly toward that light source on a moonless night than a night with the moon shining. That’s another factor in terms of when the person is driving their vehicle: Is it near the new moon? Full moon? If it’s a new-moon night, or a night when the moon is not visible, they might end up with a lot more nocturnal insects splattered on the front grill of the car and on the headlights of the car.

And it’s not something influenced significantly from year to year. It’s obviously going to be different between driving around in winter when a majority of insects are in a dormant stage, hibernating as adults or in a cocoon in the case of moths. There are going to be fewer insects in most parts of North America impacting the front windshields of cars during winter, late fall and early spring than in the mid-to-late spring and summer.

What does it say about an area if I'm hitting a bunch of them ?

If you hit them all at once it means you’ve flown through an aggregation. And flying insects aggregate for different reasons. Some species of insects have what I guess could be described as ‘mating swarms.’ This is particularly common in some species of flies like midges and they will often aggregate to find a mate. And often most individuals in big assemblages in one place will be males, and females looking for a mate will come to find a mate in a big swarm of males and usually the swarm tends to orient itself around a landmark. And another common way insects get together when looking for a mate is to do what’s called ‘hill-topping.’ In that case, they’re essentially doing the same thing that swarming flies are that hang out near a specific landmark, except that they're going to the highest point in a given region. At times when there was a lot more forests in the eastern United States, that highest point might have been the highest tree in a forest canopy, but after we cut down most of the forests it ends up often being the highest point on a hill. And biologists who study insects use that behavior to look for aggregations of males of particular species by going to the highest point in an area, and they’ll often find a lot more individual insects hanging out there, sometimes in large numbers.

But that means if you’re driving over a landscape, where the road happens to go across the crest of a number of hills — passes and the Rocky Mountains and places like that — you’re likely to hit a lot more insects when you end up driving through those areas where they’re aggregating. Other places they’ll often aggregate is along edges of streams and rivers, in the case of aquatic insects like mayflies.

Any way to tell what kind of bugs are on your car by their guts?

A field guide was written that actually enables people to do that. It’s in print. ‘That Gunk on Your Car.’ People use it to identify splattered bugs on their windshields. It was written by an entomologist at the University of Florida about 20 years ago. Mark Hostetler. It's a field guide for figuring out what you just killed. It’s a tongue-in-cheek field guide, but it’s based on actual research he did.

Watch the video: What Attracts Gnats? Why are Gnats Attracted to Me? (July 2022).


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