As their name implies, these midges cause no harm to humans – in fact the adults probably do not feed at all but they can occur in such large numbers in their “dancing” swarms just before sunset that they can constitute a nuisance.
The larvae, with their red colouration, frequently cause concern when encountered, particularly in outside lavatories, but they are harmless.
Identification of the larval breeding sites is not easy and treatment of these sites is usually very limited.
Insecticide mists may be used to control swarming adult flies.
If a sewage works is the source then treatment of the filters with a formulation approved for this use may be appropriate. This is usually carried out by the water company.
The presence of adult flies indoors may indicate that attention to proofing is needed.
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The adult flies are around 6 – 8 mm long with a wingspan of between 10 and 12 mm.
The adults are generally greyish-brown in colour, although some of them may have green bodies. It is characteristic of this genus that the wings are shorter than the abdomen and that they have no cross veins in the middle of the wing.
The antennae of the males are plumose, feathery, in appearance.
Swarming of these flies is important to mating, the swarms being largely made up of males: females fly into the swarm and mating pairs settle on vegetation. This phenomenon usually occurs at dusk.
Females lay their eggs in a mucilaginous mass in water, where the larvae are to be found.
The larvae, frequently known as bloodworms, are totally aquatic and often found in areas of low oxygen such as stagnant pools. The name “bloodworms” refers to the fact that they are frequently red in colour, signifying the presence, in their haemolymph (blood), of haemoglobin – one of the few invertebrates to have this respiratory pigment.