Insect guide > Flies > Buffalo Gnats / Black Flies

Buffalo Gnats / Black Flies


Buffalo Gnats / Black Flies(Family Simuliidae.)
These insects, known as black flies, sand flies or buffalo gnats, are small, stout, hump-backed, biting flies with broad wings and rather short legs which are sometimes speckled, and with short, straight, simple antennae. The eyes of the male are very large and frequently touch each other, and the insect in this sex does not bite.

The family contains only the single genus Simulium of which the black flies of the north woods and the buffalo gnat of the Mississippi and Missouri valleys are well known examples. They rival the mosquito in their blood-thirsty tendencies and not only do they attack human-beings, but poultry and domestic animals are frequently killed by them.

There is one case on record in which a man was killed by innumerable bites. In certain seasons they multiply enormously, alight in thousands on cattle and produce death through their poisonous bites as well as from loss of blood. Unlike mosquitoes they fly and bite in the day time and are often seen in large numbers flying in bright sunshine. The larvae are aquatic and unlike mosquitoes again, the larvae of which live in stagnant water, Simulium larvae frequent well aerated and frequently swiftly running streams. They are found most abundantly on rocks or logs so near the surface as to cause a rapid ripple.

On one occasion in the South the buffalo gnat plague was averted by the removal of a jam of logs in a sluggish bayou over which the water ran shallowly with sufficient speed to make a perfect breeding place. When the logs were removed and the old sluggish current was resumed the breeding places had been abolished. In the typical life history which follows, the issuing of the fly is mentioned but it should be stated here that with another species in the southwest a man while watching the surface of the water saw adults issue in great numbers with such force and velocity that as he expressed it they appeared as if shot out of a gun.

Typical Life History
(Simulium pictipes Hagen.)
The larvae of this species occur abundantly on the rocks in the hillside streams about ithaca, N.Y., where the writer was familiar with them as a boy. The boys who bathed in the streams in that region feared these larvae, called them leeches and supposed that they would attack themselves to the skin and suck blood.
They are, however, perfectly harmless. The life history of the species has been carefully worked out by Miss R. O. Phillips in an unpublished paper from which the following account is condensed.

The adults occur in the early part of May or at the beginning of the first continuous warm weather in the spring. The eggs are deposited on rocks over which the water is flowing. The flies hover in little swarms a foot or two above the rock, rapidly flying back and forth, and occasionally darting down and depositing their eggs beneath the water on the flat surface of the rock. The batch of eggs becomes at least a foot or more in diameter and is distinctly observable at some distance on account of the light yellowish color.

When the water is very shallow and its velocity slight the flies sometimes crawl over the surface of the rock and deposit eggs without flying. Only a small proportion of the eggs produce larvae. The larvae hatch about eight days after the eggs are laid and in this stage the insect may be found at any season of the year, in summer as well as in winter, and it is in this stage that it hibernates.

The larvae die in three or four hours when placed in quiet water. Fastened to the rock by the anal end of the body they assume an erect position and move the head around occasionally with a circling motion. They may release themselves and as they grow larger they sometimes allow themselves to be washed into deeper water, holding by a thread which they spin as they go. The thread is spun from the mouth but is attached along the side of the body to the different segments. Sometimes a large cluster of larvae will cling to the same thread which they can ascend in much the same manner as do spiders.

Not much food is taken in the winter time. During the summer the length of the larval life is about four reeks, varying with the temperature and the velocity of the water. When full grown the larva spins its cocoon, firmly attaching it to the rock and also to adjacent cocoons. The length of the pupal stage is about three weeks. Overwintering larvae transform to pupae about the 12th of April, the first flies appearing on the 2d of May. The newly issuing fly surrounded by a bubble of water quickly arises to the surface of the water and flies away instantly, the silky pubescence keeping it from getting wet.

The first generation having appeared in early May, successive generations are produced from this time on during the summer and part of the autumn. All of the flies captured from the first brood in one instance were females and this may be the rule but towards autumn the males began to appear in greater numbers and towards the last of August nearly all of the specimens taken were males. On September 2, the present writer captured fifty specimens of this fly at Ithaca and all were males with the exception of one. Adults were observed on the wing as late as the 10th of October.