How and Where do Biting Midges Live?

Like other holometabolous insects, Ceratopogonidae have four distinct life stages: egg, larva, pupa and adult. The larvae go through four instars (they shed their skin four times) before becoming pupae. In colder regions, it is generally the larvae which overwinter but our knowledge of the life cycle of tropical Ceratopogonidae is minuscule. In some regions, it appears that the adults are most common in the wet season. In many areas, the life cycle of some species may be continuous, with no apparent break in development.

To describe the various adaptations of biting midges it is useful to consider the four subfamilies found in Costa Rica separately.

The Leptoconopinae includes just one genus Leptoconops. The group is an ancient one and fossil Leptoconops are known from Lebanese amber, 120 million years old! Larvae live in wet sand (most species) or cracked, clay soils (in Costa Rica, just on coastal beaches). The sluggish larvae burrow through the sand and feed on microorganisms by raking their heads over the substrate. Adult females feed on the blood of vertebrates including mammals and birds (one species in North America feeds on lizards) and most species are diurnal feeders. The females of at least some species (including L. bequaerti in Costa Rica) have an interesting behaviour of resting under a thin layer of sand. The females of one species from the Seychelles Islands burrow into beach sand after they have acquired their blood meal and rest there until their eggs mature (3-4 days).

The Forcipomyiinae includes two genera, Forcipomyia and Atrichopogon. Larvae are aquatic, semiaquatic or terrestrial and when they are in aquatic habitats, are restricted to lentic (standing) waters. They retain the primitive anterior and posterior prolegs and therefore can walk on surfaces beneath or above a water surface. As they move, they graze the substrate surface for microorganisms. Some species feed on decaying vegetative material and a few species may be found associated with manure. In Costa Rica, there are many species which live in those epiphytes which hold some water. The larvae of most species have series of long hairs on the head and body, some of which secrete fluid. This sticky fluid is considered by most workers to provide protection against ants and other potential predators but more studies are needed.

When the larvae pupate, they retain the larval skin on the posterior end of their bodies, which is handy for those taxonomists who are studying the characteristics of the different stages. Adult females of most species suck blood from large insects and recorded hosts include katydids, stick insects, crane flies, spiders, caterpillars, blister beetles and the wing veins of dragonflies, damselflies, lacewings and butterflies. However, members of the subgenus of Forcipomyia (Lasiohelea) feed on vertebrate blood; I have seen at least one of these feeding on iguanas in Costa Rica. Some Forcipomyia (Lasiohelea) in the Old World feed on humans and one North American species feeds on frogs. Considering that there are at least seven species of this subgenus in Costa Rica, it seems likely that a number feed on other, presently unknown, vertebrates.

The Dasyheleinae includes only one genus, Dasyhelea, and members tend to be small with a wing length of less than 2 mm. The larvae are aquatic and semiaquatic and tend to be sluggish. They have posterior hooks on their abdomens and move slowly over the substrate in which they are found. Most species live in small water bodies such as those in epiphytes, treeholes, broken or damaged bamboo, rotten banana stems, fruit husks and small rock pools on the margins of streams and rivers but a few species are common in mangrove swamps and saltmarshes. Larvae may also be found in very wet vegetative material. Larvae feed on detritus and, in a few species, on carrion (dead insects). There are some species associated with rocky areas in the upper tidal zone of coastal Costa Rica but the immatures of these are not known. The adult females have reduced mouthparts and do not suck blood from either vertebrates or invertebrates; however, some species are common at flowers where they, like many other biting midges, obtain nectar from flowers.

The Ceratopogoninae includes all those species which have an elongate, legless larva (no prolegs or hooks), abdominal segments which are not secondarily divided and with a head capsule in which the mouthparts are directed anteriorly (prognathous). The larvae have a characteristic snake-like motion as they move through or on substrates. Members of this group are restricted to semiaquatic to aquatic habitats and habitats range from wet vegetation, manure, wet soil, decaying fungi and cacti, water found in epiphytic plants and treeholes, small pools, ponds, lakes, springs, streams, and rivers. In general, the earlier lineages of Ceratopogoninae (most of those in the Ceratopogonini: see "General classification of Genera of Ceratopogonidae present in Costa Rica" are in smaller habitats. Those in the Heteromyiini, Sphaeromiini and Palpomyiini (we don't know anything about the larvae and pupae of the Stenoxenini) may be found in larger bodies of water (ponds and springs and larger lotic and lentic habitats such as rivers and lakes).

In some species, the larvae feed on microorganisms but most are predators of small to large invertebrates (including large insect larvae). Smaller prey are ingested whole but in the case of larger organisms, the larvae bite into the side of ther prey, chew a hole through the cuticle and proceed to gnaw and suck up the insides of the host.

Larvae of most species swim in a characteristic rapid serpentine motion through the water column. Pupae are generally sluggish and move their abdomens slowly in more or less circular movements until they find an appropriate resting position amongst the substrate or at the water surface where their paired respiratory organs can obtain air. The pupae of some Sphaeromiini move above the water line and have specialized membraneous pads on the venter of the abdomens which they use to stick to the dry substrate.

Adult female Culicoides in the New World feed on vertebrate blood (a few species in the Old World feed on mosquitoes), although some have reduced mouthparts and do not feed at all. Almost all species tend to be crepuscular or nocturnal feeders, although there are a few which will feed during the day. For a few species, their hosts include humans and domestic animals (see section on
"Biting Midges as Pests" but we don't know what the majority of species are feeding on. One species in Costa Rica, C. phlebotomus, sucks blood from leatherback turtles as the turtles are on the beach laying their eggs; this species also sucks blood from humans and dogs and at least elsewhere in the Neotropics, transmits a filarial worm in humans called Mansonella ozzardi.

Other Ceratopogoninae females feed on other flying insects which are approximately the same size as themselves. In general, a female flies into a swarm of male non-biting midges (Chironomidae), grabs a male, either settles to the ground or surrounding vegetation and injects an enzyme which dissolves the tissues of the prey; she then sucks up the liquified contents of the body cavity (much as spiders do). In some members of the Heteromyiini, Sphaeromiini, and Palpomyiini the female enters a male swarm of its own species and while mating occurs, pierces the head capsule of the male and suck up the contents of her lover! Such females may later be found with the dried male genitalia still attached to their own abdomen, after the bulk of the dried male has broken off. Talk about a draining experience!

Within Costa Rica, it appears that most species of biting midges are in arboreal habitats. Unlike in temperate regions, where so many species may be found in larger aquatic habitats, in Costa Rica there do not appear to be many species in streams, rivers and lakes; certainly they are not there in large numbers. However, in tank bromeliads, treeholes, Heliconia flowers, old stalks of bamboo, small collections of water in old fruit husks on the ground, and in decaying fruit and vegetation, larvae may be very abundant and a large diversity of species are often present. I have found, for example, six species of biting midge larvae living in one bromeliad. In addition, in Costa Rica, there appears to be a specialized group of species which live in small seeps and springs.