The Simulidae, black flies, are small flies whose females require a blood meal for egg production (Fig. 5-48). These flies are found throughout the world, but they are more common in the cooler climates of the world. Larval development occurs in running water. The larvae are attached to the bottom of the stream by a silken strand, and are filter feeders. There are six or seven larval instars, then the larvae pupate. The adult emerges from the puparium and then rapidly bobs to the surface. The cycle takes a week or two from egg to adult. Important genera include Simulium and Prosimulium.
Black flies are vicious biters, and the scraping mouthparts rasp small holes in the skin from which the fly feeds. The flies are significant pests of humans and livestock, and they can be devastating when present in lage numbers. Some humans react quite severely to the bit of these flies, although many have no reaction or only small wheals at the feeding site. There is every reason to believe that cats also fall prey to the bites of these flies, but there have been no significant reports on the effects of these dipterans on the feline host.
Figure 5-48. Simulium. Note the short mouthparts and the shape of the antennae