Coastal area residents and visitors to Florida are often aware that something is biting, but when they look for the offender, none can be found. Sometimes they may see what appears as a speck on the skin. Florida, unfortunately, is home not only for abundant mosquitoes, but also for minute biting insects known locally as "sandflies" (elsewhere as "no-see'ums" or "punkies"), although the more correct name is "biting midges." They are especially troublesome in coastal areas, where most of Florida's population lives. Biting midges are particularly abundant in the vicinity of mangrove swamps or salt marshes.
What Are Biting Midges?
These insects are all extremely small, less than 1/8 inch long (Figure 1). They belong to the insect order Diptera (two-winged flies), family Ceratopogonidae, genus Culicoides. Florida has 47 species in this genus, but only seven are significant human pests. The four most important are coastal in distribution. Several species are associated with dairy cattle and farming operations.
Appearance, Life Cycle, and Breeding Sites
Adult biting midges are gray with distinct wing patterns. When biting or at rest, the wings are folded scissorlike over the abdomen. The eye on each side of the head is black, and the biting mouthparts protrude forward and downward. Eggs are minute, cigar- or sausage-shaped, and black. The eggs take about three to five days to hatch at 80°F.
Some species occur primarily in wet mud in and around mangrove swamps and salt marshes. Some larvae occur in the wet but not submerged mud around dairies, farms, and swine and sheep operations. The eggs, which cannot survive drying, are laid on wet mud in the breeding places, that is, the habitats where the juvenile stages (larvae) are found. The larvae develop through four stages (instars) and are creamy-white and eel-like. They are predaceous, feeding on other small organisms. Full grown larvae are 1/8 to 1/4 inch long. The total time spent in the larval stage depends on temperature and the season. When mature, the larvae change to pupae and remain in this stage for about two to three days.
Only the female midge bites and takes blood. When biting, the midge uses small cutting teeth on the elongated mandibles in its proboscis to make a small cut in the skin. At the same time, a chemical in the saliva is injected to prevent blood clotting. Capillaries severed by the cut bleed and form a tiny pool of blood, which is then sucked up. Feeding takes approximately two to five minutes. The greatest biting activity in both species is around dawn and dusk. Some biting may continue through the night, but rarely during the day, unless the sky is heavily overcast and the winds are calm.
Female midges take blood to provide a source of protein for egg production. However, females may also be autogenous, which means that some individuals are able to develop eggs immediately after they emerge from the pupal stage, without first taking blood. When blood has been taken, it is digested and the protein extracted to form eggs in the female midge's two ovaries. The number of eggs produced depends on the size of the female and how much blood she takes. Females will produce 25 to 110 eggs per bloodmeal.
Midges are primarily a warm-weather species, which begin to appear in large numbers as soon as the spring warming trend begins. Biting females are abundant throughout the summer, with numbers decreasing as temperatures drop during the fall and winter months. Depending on local conditions, some species may continue to be a pest in South Florida even during the winter.
Human Disease Transmission
Midges may be vectors of a human nematode parasite. The worm, which rarely produces symptoms of disease in infected persons, is native to South America and is found also in several islands in the West Indies. The worms live primarily in the blood, but its juvenile forms (microfilariae) are found also in the skin. Female midges ingest the microfilariae when they take blood and then transmit the parasite to uninfected persons.
Control and Personal Protection
Control of adult biting midges with insecticide sprays is mediocre at best and temporary in nature due to the continual emergence of these flies. The larval habitats are so extensive that control of the larvae is not possible. Mosquito control districts in Florida are not funded to provide control of biting midges.
On the east coast of Florida, large areas of swamp in several counties have been impounded (surrounded by dikes and kept flooded with water), an environmental method that involves changing the breeding habitat of the midges. Females no longer lay their eggs, and larvae no longer develop in the flooded mud. Impounding is an effective control method both for salt marsh mosquitoes and biting midges.
Recommendations for Bite Prevention
Avoid outdoor activity during peak biting times.
If outdoor activity cannot be avoided during biting times, apply repellents labeled for biting midges, according to the label.
Increase air movement in screened porches by using high velocity fans.
Screens can be treated with barrier sprays or portable foggers, according to the label for temporary reductions in small backyard situations.
Refer to the fact sheet on Mosquito Repellents at https://edis.ifas.ufl.edu/IN419 for details on repellents that may work on biting midges.