Way back in 2008, deer flies appeared briefly (two paragraphs) in a BOTW episode called “A few Flies,” sharing the spotlight with mosquitoes and horse flies. Amazingly, that’s the only time deer flies have appeared in BOTW, and it’s past time to flesh out their story.

Deer flies are in the family Tabanidae, the horse and deer flies, and they’re in the subfamily Chrysopsinae, the deer/sheep/yellow flies (although one source says that they should be called “human flies”). There are 120 species of deer flies in North America, with more abroad, and a combined total of 30 species of horse and deer flies live in Wisconsin (lots of write-ups treat deer and horse flies together, because their life stories are similar).

They are found worldwide, and although the fast-flying adults may wander away from them, they are tied to wetlands because their larvae grow up in the water or in adjacent, damp soils. Adults can also be found patrolling sun-dappled woodlands and edges.

How do you know you’re looking at a deer fly?��There are some scientific/microscopic measurements involved, but in general, deer flies are smaller than horse flies but larger than house flies, and many have yellow and black-striped bodies, wings with pigmented splotches on them, colorful eyes that are adapted to function well in the bright sun of late spring and early summer, and noticeable mouthparts.

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Famously/infamously, deer flies use those mouthparts to bite people and other mammals.��Only the females bite – she needs the blood to facilitate the development of her eggs.��Males are vegetarians who use their mouthparts to take nectar and pollen from flowers (she will also feed on nectar and pollen when she’s not in egg-laying mode).��The female’s mouthparts are described as “scissor like” – she uses them to make an x-shaped cut, and then she laps up the resulting blood, keeping it flowing with anticoagulants in her saliva.��Deer fly larvae are mainly carnivores that clean up on smaller invertebrates they find in water or moist soil.

Deer fly larvae are eaten by larger, aquatic carnivores like fish, predaceous diving beetles, and dragonfly naiads, and the adults fall prey to toads, killdeer, aerial insectivores like flycatchers and swallows, and dragonflies, and to wasps and hornets looking to stash them in their egg chambers as food for their eventual offspring. 

Science word of the Day: deer flies are “hydrobionts,” which means they need wet areas in order to reproduce. The dance may start with a breeding swarm where boy meets/pursues girl (in most species, the boys hatch out a couple of days before the girls). What starts in the air is consummated on the ground, and then females go looking for a blood meal before tucking masses of 100-plus eggs onto vegetation near/over water.��When the eggs hatch, the larvae (which come equipped with a “hatching spine” that helps facilitate their exit) drop into the water or onto damp soil. They may take more than a year to mature, depending on the size of the adults.

While she was doing her research, BugLady came across a few “Where are the deer flies this year?” articles (not that anyone was complaining). One attributed the low number of flies in their area to a very wet summer that flooded the breeding areas, and the other to a very dry summer that shrank the breeding areas. Deer fly pupae crawl up on plant stems or moist wetland edges just before they emerge, so too much or too little water can affect them.��One article asked why there were so many deer flies that year, and the answer circled back to a wet spring and a hot summer (apparently, when it comes to precipitation, deer flies are like Mama Bear).��Happily, they aren’t on the scene long – if mosquito season is a marathon; deer fly season is a sprint.��

Much has been written about a female mosquito’s use of our individual cocktail of odors as she zeros in on potential targets – that personal��jean es se qua��that’s made up of our CO_2,��sweat, fruity-smelling shampoo, and scented laundry detergent, deodorant, and hand lotion (it’s difficult to be unscented in the 21^st��century).��But deer flies hunt largely by eye, stimulated by the sight of large, dark, warm, moving objects (including cars), so the repellants that deter mosquitoes don’t work on deer flies. The good news is that although a number of microbes have been identified in a deer fly’s “mouth,” there’s only one disease they are known to transmit in North America – tularemia (aka rabbit fever) is spread by deer flies in the western US.��

The pain from a deer fly’s bite is in bee sting territory (it’s been described as “poking a red-hot needle into your skin”).��Her saliva may cause further pain and itching, and some people are allergic to deer fly bites.��If DEET won’t do it, what will?��Dressing for success helps, in light-colored, loose-fitting long sleeves, long pants, and a hat (because when deer flies check us out, they start at the top), and some folks add mesh netting over the cap.��Some swear that deer flies are attracted to the color blue.��Several sources promised that deer flies are inactive at temperatures under 70 degrees F, but others laughed at that notion.

People have gotten pretty creative in aid of avoiding deer flies, using devices that are homemade and store-bought, sacred and profane, and just plain embarrassing.��Sticky patches to attach to your hat, and hats with built-in sticky patches are easy to find in sporting goods stores (see picture ), or you can DIY with loops of duct tape.��One author wrote of spreading sticky stuff like Tanglefoot on a cup (think red or blue 16 oz Solo cup) and taping the cup to the top of his hat on his walks.����

The BugLady wears a hat on her perambulations, and she enjoys listening to the deer flies bouncing off of it. 

Here are a few gems that the BugLady found while she was Googling.

From the Missouri Department of Conservation:

“In the 1800s, the upland prairies of Missouri’s Audrain County were late to be settled in large part due to the presence of these insects. The WPA-produced Missouri: A Guide to the “Show-Me” State (1941) put it this way: ‘At certain times of the year, the flies made day travel impossible, and even plowing and other farm work had to be done at night.’ Many other prairie regions in the American Midwest had similar problems with tabanid flies; in some cases, horses were said to be driven mad by the incessant attacks of horse and deer flies.”

From the Audubon Beidler Forest website:

“If you were to ask me which cloud of biting insects I would prefer, mosquitoes or deer flies? Well, you can outrun mosquitoes. Running away from deer flies just gets them excited.

A deer fly is also characterized by its ability to withstand a fairly good smack after it lands on a person and begins to bite. Often the fly falls lifelessly to the ground after being struck, yet within a few seconds uprights itself and then eventually takes to the air again in an attempt to make another attack.”

From Michigan State University Extension:

Deer flies “apparently have their place in U.S. history: Ross Arnett, author of , reports the following. ‘It is said the Declaration of Independence was signed by July 4, 1776 instead of a later date that would have permitted further discussion because the horse flies in Philadelphia were biting so fiercely at the time that the delegates decided to adjourn just to get away from them.’�ĝ

And finally, from “the World Around Us” podcast and blog, which “seeks to arouse your sense of wonder and motivate you to act on behalf of nature at every opportunity.”:

Blogger Sarah O’Malley reminds us that every organism has a job to do, and that deer flies do theirs very well.��She concludes that, “No body likes hanging out with deer flies. But all the same, I prefer a world where they exist, a world as full as it can be with as many different kinds of organisms as possible, a world rich and damp and squirming with life. That is truly the point of it all, and we can’t do it without the biters and scratcher anymore than we can do without the cute furry babies and the fluffy little birds. They all count, every last knife like mouthpart wielding one.”

Thanks to BugFan Sophie for taking the picture of the cute little deer fly on the BugLady’s hat.

The BugLady

PS – BOTW was born (as a joke) back in August of 2007.��What with the reruns and the time-outs, it’s taken a while to get here, but this is, by the BugLady’s count, episode #800.�� Thanks, BugFan Patrick – and we’re both still going strong! (-ish)

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2025 – almost two decades ago, when the BugLady was working on a phenology project in the Bog, she encountered multitudes of mosquitoes and she made a deal with them – she wouldn’t bite them if they wouldn’t bite her. Sometimes it works, sometimes it doesn’t, and sometimes she is in the presence of someone who is far more tender and juicy than she is. She’s leading a field trip at the Bog soon, and she’ll find out if everyone remembers the deal.

Mosquitoes have been discussed in a number of BOTWs –  and Psorophora Ciliata aka The Shaggy-Legged Gallinipper – Field Station – this is the first (with a few new words and pictures).

And remember – bug zappers don’t kill mosquitoes. The New York Times Wirecutter section says, “Bug zappers kill bugs by the thousands. But there’s a problem: They kill the wrong bugs. They are ineffective against mosquitoes and other biting flies, and their otherwise indiscriminate killing can disrupt pollination and generally throw the environment out of balance. Plus, the force of their electrocution can spew a mist of disease-ridden bug parts out into the air.”

2014 – Who hasn’t seen the postcard (and keychain and license plate holder and t-shirt and coffee mug) that trumpets the mosquito as our state bird? It’s the insect we all love to hate (they are the very definition of the word “swarm”), but behind the legend lies a fascinating animal.

Yes, there are a lot of them – about 3,500 species worldwide, 175 in North America, and 50 in Wisconsin. Mosquitoes (mosquito is Spanish for “small fly.”) are in the Order Diptera (“two wings”) and they are in the family Culicidae. Some people think they’re kind of pretty (including the BugLady, when she’s not inhaling them). 

Yes, they grow up fast. Eggs are laid on the surface of the water, on floating leaves, or in a spot just above the water line that will subsequently flood. They generally hatch in a few days, and it takes about month to morph from egg through larva (called a “wiggler”/”wriggler”) (because twitching is their mode of locomotion) through pupa (“tumbler”) (because their mode of locomotion is tumbling) to adult, but in some species, development is telescoped into 10 days. Mosquitoes don’t live very long – males for about a week and females for two or three. Depending on species and location, there can be several generations per year. 

Some species of mosquito overwinter as fertilized females in sheltered spots (or in basements, which explains why the BugLady sees the odd mosquito flying around her house in January), and they’re raring to go when spring comes. Other species may overwinter in a state of delayed development called diapause in any of the above stages, resuming growth when the water warms in spring. 

Yes, they are adaptable. Eggs develop in wetlands but also in birdbaths, puddles, pails, flower pots, old tires, and the dog’s outside water dish (if you put water in it, they will come). The first line of defense in knocking down residential mosquito populations is getting rid of these man-made sources of standing water. 

Yes, they do bite. Females mate only once, but they may lay several “clutches” of eggs. Males, newly emerged females, and non-egg-laying females feed on nectar and other plant juices, but before each cluster of eggs that she lays, a female must ingest a (high-protein) blood meal (in some species, the blood-letting starts with the second batch of eggs). Some mosquitoes include humans on their list of possible donors; others restrict themselves to birds, reptiles, amphibians, or non-human mammals. 

She injects, with her saliva, small doses of anticoagulant and anesthetic to aid the process (the resulting red, itchy bump is caused by your body’s histamine reaction to the injected proteins). Then she ingests so much blood that taking off seems impossible. A mosquito’s abdomen has expandable tissue between each segment and also between the harder upper and lower surfaces of each segment, so it stretches both vertically and horizontally. 

The BugLady once found a decent-sized snapping turtle digging a hole to lay her eggs in at dusk and, of course, got as close as she could to get some pictures without disturbing the process. She was AGHAST when she put the pictures up on the monitor and saw that the soft (but still armored) parts of the poor turtle were covered by tiny mosquitoes, and that they were even on her shell. And that the grass around the turtle’s head was littered with mosquitoes that were too bloated to fly! 

Most mosquito wigglers eat the algae, bacteria, debris, and zooplankton that’s floating around in the water with them. Some species are predators, and a few even eat the larvae of other mosquitoes. Wigglers are important food chain “middlemen” between the tiny organisms they feed on and the fish, amphibians, reptiles, birds and the other aquatic insects that prey on them. Adult mosquitoes are an essential food for bats, birds, dragonflies and damselflies. 

Yes – Female mosquitoes of some species are notorious transmitters of diseases caused by various viruses, protozoans, and nematode worms (the warmer winters we’re having due to Global Climate Change are allowing some tropical diseases like dengue fever to move north again as the mosquitoes that carry them extend their range). These causative agents generally set up shop in the mosquitoes’ salivary glands, which ensures a free ride into the blood donor’s body (Remember to give your dog it’s heartworm medication). 

More fun facts about mosquitoes:

• That annoying hum is actually a love song. He sings alto, and she sings tenor, and when they hear each other (they sense sound with their antennae, and the male’s antennae are quite fancy) (some males have big, hairy palps -sensory adjuncts to the mouthparts – too), they vary their tone – by changing the frequency of their wing beats – until both are humming at the same pitch. Romance ensues.
• Some species of mosquitoes prefer to lay their eggs in the seclusion of a small pool of water that is trapped in a plant; these reservoirs are called phytotelmata&�Բ�����;(“phyto” means plant and “telma” means pond) (the singular is phytotelma). A specialized bog species, the harmless pitcher plant mosquito (Wyeomyia smithii) grows only in the water of the purple pitcher plant (Sarracenia purpurea). Tropical species of Wyeomyia develop in bromeliad “tanks.” Holes in trees where rainwater collects are a common kind of phytotelma.
• Wyeomyia smithii turns out to be a pretty interesting critter. Its eggs are deposited in the new leaves of pitcher plants. The larvae/wigglers are considered top predators in the community of organisms that inhabits the pitcher plant’s water reservoir. They feed on bacteria and mini-animals in the pitcher plant’s water, and while they do eat some of the bits of partly decomposed insects that were meant to nurture the pitcher plant, they feed on organisms that feed on bacteria, ensuring a diverse crop of bacteria to decompose the insects that fall into the pitcher plant’s water. They overwinter in the pitcher as larvae, frozen in its water. For a thorough biography of the PPM, see .
• There’s even a mosquito that helps with mosquito control. Elephant/treehole mosquitoes in the genus Toxorhynchites are big, primarily tropical, mosquitoes. According to , one species, Toxorhynchites rutilus , ranges from Connecticut to Florida to Texas to Kansas. Turn them loose, especially in a manmade water tank, and they will feed on the wigglers of other species (and of their own), and they do not require a blood meal. Everything one might want in a mosquito! 

And yes, for reasons that are not completely clear, mosquitoes are more attracted to some people than to others. A lot of scientific experiments have been done and anecdotal explanations offered (an individual’s general “sweetness” of temperment is apparently not a factor). It may be a response to clothing color (they prefer dark), perfumes (love ‘em!), blood type (they prefer Type O), pregnancy (yes), body heat, particularly aromatic sweat, and/or distinctive carbon dioxide exhalations. Ms. Mosquito can detect CO₂ in the air from 25 yards away and home in on the source. 

And by the way, the BugLady would like to suggest that whoever keeps writing “Mosquitoes are crepuscular – active at dawn and dusk – and they rest during the heat of the day” has only visited God’s country in the snow. 

The BugLady

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