There are several important roles which biting midges play in ecosystems. As larvae, many are predators in aquatic and semiaquatic habitats where they can occur in very large numbers. The most speciose group, those in the subfamily Ceratopogoninae, have larvae which are like small snakes, which work their way slowly through the wet substrate and then lash out at prey. Some prey is swallowed whole but in the case of larger prey for species in some genera, which are mostly other insect larvae, the biting midge larva burrows through the cuticle of the host and eats its insides. It seems certain that in many habitats, biting midge larvae are an important biological control on other insects but this has not been studied. A good project to investigate this would be to examine the larvae found in tank bromeliads where larvae are quite common and living with a number of other groups. In streams and rivers larvae may be an important source of food for other invertebrates and fish.
Biting midge adults are important pollinators of a number of plants. In some tropical countries the most notable of these is cacao, the source of chocolate, of which members of the genus Forcipomyia are the primary pollinators. Limited evidence indicates that Hevea (rubber tree), a number of palms, and mango are all visited by large numbers of biting midges. It appears from scattered observations in various regions (including temperate), that the small flowers of many shrubs and trees attract biting midges and it seems likely that many are important as pollinators of these; in spite of some excellent studies on a few plants, there is virtually an open field of research to study this further.
Female adults of many species in the speciose genera Atrichopogon and Forcipomyia are ectoparasites feeding on the blood of insects much larger than themselves, such as katydids, stick insects and on the wing veins of dragonflies and Lepidoptera (mostly butterflies). There have been suggestions that the flies may actually be involved in transmitting viruses from one insect host to another (particularly between caterpillars) but this has never been studied in detail.
Females in the subfamily Ceratopogoninae on the body contents or blood of other insects but usually only those that are about the same or smaller in size. Most of these prey are swarming nematocerous Diptera (mostly non-biting male midges of the family Chironomidae) which are captured by females which fly into the swarm to grab an individual. Often the female and prey fall to the ground or settle on nearby vegetation where the female injects an enzyme into the body cavity. This dissolves the body contents of the prey and the female then proceeds to suck out the contents, leaving an empty carcass behind. The females of species of some genera fly into male swarms of their own species and, during copulation, inject the enzyme and suck out the body fluids of the male. The male genitalia is then left clasped on the female genitalia, acting as a barrier to mating with other males, and breaks off the body of the otherwise empty husk of the male’s body!