Bite of the Black Fly

It happened at the zoo. I was parked innocently opposite the African Elephant yard, with the window rolled down on this nice late afternoon of September 19, 2015, waiting for Heidi to get off work. I noticed a tiny fly had flown into the car, but was truly shocked to see it was a female black fly, likely a species of Simulium....and she wanted my blood.

She got it, too, because I so rarely see members of the family Simuliidae, let alone adult females. I was able to get some respectable images of the 3-4 millimeter vampire precisely because she was occupied pumping blood out of my knuckle. What was she doing here, though?

I was under the mistaken impression that black flies, also known as "buffalo gnats" and, here in Colorado at least, "turkey gnats," seldom venture far from fast-flowing streams and rivers. That is because they spend the egg, larva, and pupa stage of their lives in aquatic torrents. It occurred to me that the elephant yard does have a waterfall, and I would bet that black fly larvae live on the very edge of that artificial cataract.

Well, I have since learned that female black flies are perfectly capable of flying miles in search of a blood meal. There are some records in Canada of black flies migrating over ninety (90) miles from where they grew up as larvae.

Only the female black fly bites. Like mosquitoes, she needs the protein for the proper development of her eggs; and she can lay several hundred eggs in her two- or three-week adult lifespan. Unlike mosquitoes, black flies do not have beak-like mouthparts to extract blood from our capillaries. Black flies slice you open with knife-like mouthparts, then lap up what spills out.

Depending on the species, the black flies lay their eggs on vegetation or other objects in the water, under the water, or scatter them on the water's surface. Interestingly, freshly-laid eggs apparently produce a pheromone (scent) that attracts other adult female flies of the same species, and stimulates them to lay their eggs in the vicinity.

The larvae that hatch spin silken pads on the surface of stones or vegetation in the middle of flowing water. They then anchor themselves to the silk pads with special hooks on the rear of the abdomen. The larvae feed in a unique manner, by deploying a pair of "cephalic fans" that intercept organic particulates from the current. Larvae molt 7-11 times.

Black fly larvae in Arizona

At the end of its larval life, the creature spins a silken bag in which it will pupate. The tapered rear of the bag points upstream into the current, while the wider, open portion projects downstream. The larva molts one final time to reveal a resting stage with branching gills that may reach beyond the lip of the silken bag.

Black fly pupae in Arizona © Tony Palmer

The adult fly emerges in a few days or so, rising to the water surface in an air bubble and floating to an emergent object it can climb onto and finish expanding its wings and hard its exoskeleton. The total time from egg to adult takes roughly 3-4 weeks and is heavily influenced by water temperature. The colder the water, the longer the life cycle. There can be three or four generations per year; winter is typically spent in a dormant larva stage.

Male black fly (note huge eyes meeting at top of head)

There are about forty species of black flies in Colorado, in three genera: Simulium, Prosimulium, and Metacnephia. Different species live at different elevations, and on different sides of the Continental Divide. Surprisingly, the majority are not pests of people or livestock, preferring to feed on birds and other wildlife.

The species that do afflict horses, cattle, poultry, and people can cause severe distress, and may carry diseases. I will spare you the agonizing details of suffering incurred by victims of black fly attacks, as there is no end to the resources where you can learn such information if you are so inclined.

Suffice it to say that it pays to be prepared with an excellent insect repellent if you plan to be in black fly territory. Prevention is always the best tactic for battling *any* bloodsuckers. Take care.

Female black fly on Feb. 24, 2014

Sources: Bechinski, Edward John, and Marc J. Klowden. 2005. Black Flies - Biology and Control. Division of Entomology, University of Idaho (available online as a PDF).
Cranshaw, W.S., F.B. Pearis, and B. Kondratieff. 2013. Biting Flies. Colorado State University Extension. Fact Sheet 5.582.
Kuhn, Dwight. "Black Flies - Life Cycle," Kuhn Photo.

The Stable Fly

Of all the biting flies we have in North America, one of the most annoying has to be the Stable Fly, Stomoxys calcitrans. They are especially abundant around farms, ranches, zoos, and other places where large mammals are kept. Unfortunately, they will also bite people when livestock is not close at hand.

Like any notorious villain worth their salt, the Stable Fly has it aliases: "beach fly," "dog fly," and "lawn-mower fly" among them. The insect has also fled local jurisdiction. It is apparently native to Eurasia and Africa, with speculation that it probably came to the New World in colonial times, maybe in ship's ballast.

The Stable Fly is easily dismissed as a House Fly under cursory examination. Both flies are in the family Muscidae; and both are about the same size, the Stable Fly measuring 5-7 millimeters. Each species is mostly gray, with black "pinstripes" down the back of the thorax. The Stable Fly differs mostly in having a slender, black, slightly curved beak tucked under its "chin."

Proboscis (painfully) deployed!

While it is only the female mosquito, black fly, deer fly, and horse fly that sucks blood, both genders of the Stable Fly can bite. This is not a painless event, either. An immediate, sharp sensation occurs when the fly plunges its piercing mouthparts into your skin. Shoo it away and it returns instantly, and repeatedly. This persistence is perhaps the main source of our aggravation.

Commencing feeding

Almost full!

The adult fly is only one quarter of the life history of the species of course, with eggs, larvae, and pupae making up the other three stages in its metamorphosis. The female fly deposits her eggs singly, or in clusters of 25-30, in wet, decaying fibrous organic matter. Typical breeding material includes horse manure, silage, rotting hay, grass clippings, and partially composted livestock bedding.

Female full of eggs

The eggs hatch in one to fourteen days. The maggots that emerge take anywhere from 11-30 days on average to mature. The interval is largely determined by temperature, humidity, and food quality and quantity. The hotter and more humid the substrate, the faster the maggots develop. The maggot molts twice after hatching, and may be up to twelve millimeters in length by the time it enters the pupal stage.

The pupa represents the larva's third molt, the shed exoskeleton of which forms a hard, oval, dark brown "capsule" around the pupa itself. The pupal stage typically lasts six to twenty days. The adult fly then bursts out of its capsule by more or less inflating the front of its head.

Stable Flies will also sip flower nectar

The determination of Stable Flies in their feeding behavior naturally induces stress in its victims, and this can take a toll on livestock. A mere twenty flies on a cow can result in decreased milk production. Mild anemia and weight loss can also be a result of high numbers of feeding Stable Flies.

Were it such that general malaise was the only negative effect of Stable Fly populations, it would possibly be tolerable. Unfortunately, Stomoxys calictrans can also carry a variety of diseases. Most of these are of limited effect in the U.S., thankfully, but they cannot be dismissed entirely. Here, the fly can transmit anthrax, which affects livestock, pets, and people. Anthrax exhibits a variety of symptoms, the worst of which include lesions of the lungs or brain.

The next time you visit a local farm, ranch, or zoo, you might want to consider applying that DEET-based insect repellent to help fend-off attacks of Stable Flies. It will make your experience much more enjoyable if it is bite-free.

Sources: Cumming, Jeffrey M. 2006. "Diptera Associated With Livestock Dung," North American Dipterists Society.
Newberry, J. 2003. "Stomoxys calcitrans" (online), Animal Diversity Web.

New Report on Chagas Disease Causes Storm of Concern

There has been a great increase in concern, and spread of misinformation recently in response to a press release and policy paper earlier this month. The publication advocates for more research into Chagas disease, caused by a parasitic organism, Trypanosoma cruzi, carried by assassin bugs in the subfamily Triatominae. The result in social media especially has been the misidentification of nearly every indoor "bug" or assassin bug as a "kissing bug" carrying Chagas.

Our most common U.S. "kissing bug," Triatoma sanguisuga

I wrote about our U.S. species of Triatoma in an earlier blog post, and that information remains largely correct. The post also includes information about species regularly confused with Triatoma species.

There is no question that it is in the best interest of governments and scientific institutions to devote more resources to treating and preventing tropical parasitic diseases as the climate continues to warm and new disease vectors spread northward; and as parasitic organisms develop resistance to conventional medicines. The elephant in the room, however, is the increasing population of human immigrants to the northern hemisphere in response to economic suffering and political violence or unrest.

Rural poverty continues to be the reason that many parasitic diseases proliferate, and the driving force behind immigration to nations experiencing relative prosperity and economic opportunities not found in the countries from which immigrants originate.

Victims often carry Chagas disease without showing obvious symptoms, serving as a reservoir for the parasite. Pets, especially dogs, and livestock can also carry the parasites responsible for Chagas. This should not make immigrants, legal or otherwise, enemies of native U.S. citizens, but I fear it is only a matter of time before it becomes a political football, just another excuse to "reform" our immigration policy.

Furthermore, our native species of Triatoma are poor vectors of the disease, which is transmitted when the insect defecates while feeding. The victim of the bite then scratches the parasite-infected feces into the bite wound, or may absent-mindedly rub their eye or other mucous membrane. Our kissing bug species are "potty trained" and nearly always poop after they have left their host.

My friend Richard Fagerlund gave a succinct and accurate assessment of the status of kissing bugs in New Mexico for a television news report, but his advice applies to the rest of the southern U.S. as well: There is simply nothing to be concerned about in urban areas, and simple preventive measures in rural areas, such as keeping your property free of wood rats, almost completely eliminates the prospect of encountering them.

Please help me spread the message that there is no need to panic, especially at this time of year. Kissing bugs are late spring and summer insects, only rarely showing up in autumn. If you are finding an insect in your home right now, it is almost certainly not a Triatoma.

The Black Corsair

Turn on an outdoor light anywhere in the eastern U.S. at night at this time of year and you are likely to attract one, if not several, individual males of the assassin bug known as the “Black Corsair,” Melanolestes picipes. Why only males? More on that in a moment. What are they doing there? They are likely looking for other insects to prey upon.

This species exhibits what is called sexual dimorphism. Adult males are fully winged and are strong fliers. Females usually lack hind wings and have the front wings reduced to mere pads, though there are exceptions. They are nocturnal, like the males, hiding under stones, boards, and other objects by day.

Female M. picipes, Taney County, Missouri

This is among one of the most abundant assassin bugs in the United States, found from New England to Florida, and west to Colorado, Utah, and California. It is often confused with the Masked Hunter, but the Black Corsair averages smaller, at 15-20 millimeters in body length.

Most specimens from the northern part of its range are wholly jet black, but southern specimens may have a red or orange edge to the abdomen, or even have the abdomen entirely red. Those specimens are sometimes confused with the bordered plant bugs I wrote about last week. The red-bordered forms of Melanolestes picipes were formerly considered a separate species, M. abdominalis. The two are now recognized as a single species.

Male M. picipes, Taney County, Missouri

A highly distinctive feature of these agile assassin bugs are the “ankle weights” or “leg-warmers” they seem to be wearing on the first and second pair of legs, at the distal end of the tibial (“shin”) segment. The inflated attribute is called the fossula spongiosa, a pad composed of a dense mat of hairs, with pores beneath them that exude a thin film of oil to the flared tips of the hairs. The whole affair allows the bug to chase prey over slick substrates, cling to struggling victims, and grip a mate in the case of males.

M. picipes from Cape May, New Jersey, after a bad molt

Be careful that you don’t ever mindlessly swat one of these insects if it lands on you. The defensive bites of assassin bugs in general are excruciating, and the odds of being bitten go up when the Black Corsair comes to town. Because they are attracted to lights, and run and fly with great speed and agility, the males may find their way indoors.

It is just this scenario that played out in the notorious “kissing bug scare” in the summer of 1899 in the eastern United States. Accounts vary, some stating the panic began with a single incident of a woman being bitten in Washington, DC (Freiberg, et al, 1984); others claiming there really was a higher incidence of bites from bugs that year. That sensationalized newspaper reporting helped fan the flames of paranoia is a subject of unanimous agreement. Whether the assassin bug responsible was the Black Corsair, or the Masked Hunter, neither species would have been lusting after human victims, simply looking for insect prey in the wrong places.

Male M. picipes, Manhattan, Kansas

Sources: Berenbaum, May. 2009. “Kiss and telmophage,” Am. Entomol.. 55(2): 68-69, 112
Freiberg, Marcos and Jerry G. Walls. 1984. The World of Venomous Animals. London: T. F. H. Publication, Inc. Ltd. 191 pp.
McPherson, J.E., S.L. Keffer, and S.J. Taylor. 1991. “Taxonomic Status of Melanolestes picipes and M. abdominalis (Heteroptera: Reduviidae),” Fla. Entomol. 74(3): 396-403
Slater, J.A. and R.M. Baranowski. 1978. How to Know the True Bugs. Dubuque, Iowa: Wm. C. Brown Company Publishers. 256 pp.