{"id":11176,"date":"2019-12-18T12:12:23","date_gmt":"2019-12-18T18:12:23","guid":{"rendered":"https:\/\/uwm.edu\/field-station\/?p=11176"},"modified":"2019-12-18T12:12:23","modified_gmt":"2019-12-18T18:12:23","slug":"horsefly","status":"publish","type":"post","link":"https:\/\/uwm.edu\/field-station\/bug-of-the-week\/horsefly\/","title":{"rendered":"Horsefly"},"content":{"rendered":"

Howdy, BugFans,<\/p>\n

The first rule of finding insects is \u201cLook on flowers.<\/em>\u201d Flowers provide a place to rest, as well as a place to eat and be eaten. The second rule is \u201cif you see an insect that\u2019s really still (or in an odd position), look for a predator nearby.<\/em>\u201d So, when the BugLady spotted a horizontal horse fly, she knew that something was afoot, and she soon located the ambush bug above and to the left of the fly (the fly\u2019s eyes were a bonus).<\/p>\n

Back in November of \u2018aught-eight,\u2019 the BugLady wrote briefly about horse flies in a survey of biting flies, click here to learn more<\/a>. It\u2019s a group that we love to hate, but hey, it\u2019s December, and we can consider them cerebrally rather than emotionally.<\/p>\n

Horse flies are in the fly family Tabanidae<\/em>, which also includes the deer flies. One source noted that while both horse and deer flies buzz on approach (deer flies\u2019 whine is higher-pitched), horse flies aim at bare skin below the knees, and deer flies like the back of your neck. The BugLady, whose field clothes are long pants and short sleeves, is going to have to mull that one over a bit. According to bugguide.net<\/a>, colloquial names include \u201cBulldog Flies, Clegs, Yellow Flies of the Dismal Swamp, Greenheads, Gad Flies, and Copper Heads<\/em>.\u201d And undoubtedly other names that wouldn\u2019t make it past the NBC censor.<\/p>\n

\"Tabanid\"<\/p>\n

There are about 4,500 Tabanid<\/em> species worldwide – 350 in North America. They\u2019re found around the globe except for Hawaii, Greenland, Iceland, and the Polar Regions. Our most familiar horse flies are in the genus Tabanus<\/em> (pronounced Ta-BAY-nus),<\/em> which has about 100 representatives in North America. They\u2019re often encountered around permanent wet\/moist-lands because that\u2019s where their somewhat aquatic offspring live, but they can be found from deserts to mountaintops.<\/p>\n

Tabanids<\/em> tend to be chunky flies, and some of them, at an inch-plus in length with a two-inch wingspan, are sizable. Their eyes are sometimes described as \u201cbulging\u201d (male flies have those huge, wrap-around eyes; females\u2019 eyes are separated). Deer flies tend to be more colorful than the usually-drab horseflies (but read on).<\/p>\n

\"Horsefly<\/p>\n

Male horse flies feed on nectar and pollen and don\u2019t have the equipment to bite. Females drink nectar, too, but they also need a blood meal (mostly from a mammal) to help them produce eggs. So they ambush passers-by, zeroing in on large, dark-colored, moving objects that give off a cloud of CO2 (including motor vehicles, says Eric Eaton, in The Kaufman Field Guide to Insects of North America<\/em>) (clouds of deer flies around the side mirrors of slowly-moving cars are a common sight in July in the habitats where the BugLady hangs out).<\/p>\n

Wikipedia describes their mouthparts as \u201ca stout stabbing organ with two pairs of sharp cutting blades, and a spongelike part used to lap up the blood that flows from the wound<\/em>.\u201d Anticoagulant saliva keeps the blood flowing, sometimes long after the fly has departed. Some females may need a second meal or are disturbed during the first meal, and it\u2019s in biting a second victim that she may transmit diseases (the list of pathogens isn\u2019t long, and human infection is rare here in Wisconsin). Some people are allergic to the bites, though, and cows that are under attack by Tabanids<\/em> are not <\/em>contented – both weight gain and milk production suffer.<\/p>\n

\"Horsefly\"<\/p>\n

Horse flies are not without predators \u2013 birds eat both adults and larvae; nematodes and wasps parasitize the larvae, and adults are captured by solitary wasps to provision their egg caches and by spiders. Click here to read more.<\/a><\/p>\n

We swat at them without really looking at them, but if we didn\u2019t know what they do for a living, we might notice that they\u2019re pretty a handsome and diverse bunch of flies\u2026… https:\/\/bugguide.net\/node\/view\/1090460\/bgpage<\/a>, and
\nhttps:\/\/bugguide.net\/node\/view\/1638079\/bgpage<\/a>, and
\nhttps:\/\/bugguide.net\/node\/view\/285005\/bgpage<\/a>, and
\nhttps:\/\/bugguide.net\/node\/view\/928300\/bgpage<\/a>, and
\nhttps:\/\/bugguide.net\/node\/view\/428918\/bgpage<\/a>, and
\nhttps:\/\/bugguide.net\/node\/view\/1522330\/bgimage<\/a>, and
\nhttps:\/\/bugguide.net\/node\/view\/241451\/bgpage<\/a>,<\/p>\n

\u2026and that they have eyes that macro photographers love,
\nhttps:\/\/bugguide.net\/node\/view\/967345\/bgpage<\/a>, and
\nhttps:\/\/bugguide.net\/node\/view\/327405\/bgimage<\/a>, and
\nhttps:\/\/bugguide.net\/node\/view\/951612\/bgpage<\/a>, and
\nhttps:\/\/bugguide.net\/node\/view\/241723\/bgpage<\/a>, and
\nhttps:\/\/bugguide.net\/node\/view\/123186\/bgpage<\/a>, and
\nhttps:\/\/bugguide.net\/node\/view\/1572514\/bgimage<\/a>.<\/p>\n

(Why? Click here to read more<\/a>.)<\/p>\n

\"Horsefly<\/p>\n

Males chase females aerially after spotting them with those magnificent eyes. She lays her eggs in clumps that may contain as many as 1,000 eggs in several layers. Egg masses are glued to vegetation, rocks, twigs, etc. over the water; the BugLady usually finds them on cattail and blue flag leaves. The tiny larvae are equipped with a spine that helps them exit the egg, and when they hatch, the larvae fall into the water (deer flies) or onto moist ground (horse flies). There they stay, sometimes for several summers, especially in the north, feeding on small, soft-bodied insects and crustaceans, subduing them by biting them and injecting a venom. Click here to read more<\/a>.\u00a0(and like their elders, they\u2019re capable of delivering quite a bite, themselves, when handled carelessly).<\/p>\n

Horse flies have been bothering people since there have been people, and if you\u2019re on board with the idea that some of the dinosaurs were actually warm-blooded, ancestral horse flies may have fed on them, too. Aeschylus, a Greek playwright who died around 456 BC, wrote that horse flies drove people to madness.<\/p>\n

\"Ambush<\/p>\n

The BugLady indulged in some picture-keying, which is unreliable but is so much fun when done responsibly. She thinks that the ambush bug\u2019s victim may be Tabanus marginalis<\/em>, which bugguide.net<\/a> calls \u201cthe most common biting fly throughout the world<\/em>\u201d (but has only three pictures of). It\u2019s a mostly-northern species with disjunct populations along the Appalachians, and it likes cool, wooded swamps.<\/p>\n

The horse fly on the gravel path could be Tabanus nigripes<\/em>, whose larvae are at home in wet areas that contain lots of organic material, like drainage ditches. The Tabanidae of Florida<\/em>, by Jones and Anthony, tells us that \u201cin recreational areas adjacent to lakes where livestock is not present, this species is reported to be a serious threat of man<\/em>.\u201d<\/p>\n

\"Horsefly\"<\/p>\n

The horse fly on the green leaf is (possibly) Tabanus vivax<\/em>. One source says the larvae like boggy habitats, but a 1905 publication calls it the River horsefly and says that the larvae have been found in riffles.<\/p>\n

The robust little, bullet-shaped fly with the dark stripe on its abdomen, sitting on a wood boardwalk, is probably Hybomitra illota<\/em>, a horse fly of more northern orientation (mid-America, north). The BugLady found an interesting paper by P.D. Taylor and S.M. Smith in Medical and Veterinary Entomology<\/em> about the breeding behavior of males. Under certain weather conditions, males aggregate in large groups at \u201cmating areas<\/em>.\u201d Their behavior is somewhat similar to the lek behavior of some birds. Hybomitra illota<\/em> is known to bother humans.<\/p>\n

But not in God\u2019s Country in December.<\/p>\n

The BugLady<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

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