Dark Winged Fungus Gnat

Die muggies kom van buite
En vrek dan teen die ruite…
(With apologies to Koos du Plessis)


Did you also have an infestation of tiny flies this winter, with scores of minute dead bodies on the window sills?

Photos by Dr Vic Hamilton-Attwell

These small Dipterans (two-winged insects such as house flies and mosquitoes) were identified by Dr Vic Hamilton-Attwell as Dark-winged Fungus Gnats. They are members of the Mycetophilidae, which translates into fungus lovers. It was undoubtedly the very wet weather of the last few months that caused a population explosion of these gnats: they breed in damp soil that’s rich in organic material, especially in wetlands and around pans like the Vermont salt pan. The nutrient-rich damp soil promotes the growth of fungi in the soil, which is what the gnat larvae love to feed on.


These delicate insects are very small in size, typically measuring around 2 to 5 millimetres in length. They derive their name from their dark-coloured wings, which are often adorned with intricate patterns. Their bodies are slender, and they have long, delicate legs. Although they are often mistaken for mosquitoes due to their similar appearance, dark-winged fungus gnats don’t bite and are thus harmless to humans.

At first glance it would seem that fungus gnats have very little value in life, except to annoy humans. Not so.

Despite their small size and inconspicuous nature, these gnats play a vital role in the ecosystems they inhabit. The larvae primarily serve as decomposers, contributing to the breakdown and recycling of organic matter. By feeding on decaying plant material, they accelerate the decomposition process, which releases essential nutrients back into the environment.

Adult fungus gnats also serve as pollinators for various plant species. As they move from flower to flower in search of nectar, they inadvertently transfer pollen grains.

Interestingly, some species of orchids do not produce nectar as a reward, but release pheromones resembling those of female fungus gnats. The male gnats are attracted by the chemical signal and try to mate with the flower. This triggers the flower to close, trapping the gnat inside. The gnat’s escape route is through the sexual structures of the flower. As it does so and visits various flowers, it deposits pollen on the stigma and gathers new pollen from the anthers to transfer to another flower.

As is the case for all insects, the life cycle of the dark-winged fungus gnat consists of four stages: egg, larva, pupa, and adult. Adult females lay about 200 transparent eggs (each about 1 mm long) into moist soil or decaying organic matter, such as leaf litter or fallen logs. Once hatched, the larvae begin their feeding frenzy, voraciously consuming fungi and other organic matter and contributing to its decomposition.

After about one week, the larvae hatch. Intriguingly, about 90% of the larvae are female – this is as a result of Paternal Genome Elimination (PGE). This process is found in several insect species (as well as certain flowers and even mammals). The male suppresses his male DNA and passes on only the genetic material of his mother to his offspring, resulting in predominantly female larvae. So when conditions are favourable, the predominantly female population will reproduce very rapidly, resulting in the kind of “infestation” we experienced recently.

The larvae are transparent and legless, with distinct black heads and a series of segments along their bodies. But being legless doesn’t mean they can’t travel. Several species, especially Sciara militaris, use an intriguing method of moving overland if they have to seek new foraging. They migrate in processions of thousands of individuals. The larvae line up and clump together, all facing in the same direction, forming a shape resembling a slug. By coordinating their movements within the group, they move forward.

After a period of growth and development, the larvae enter the pupal stage. During this time, they undergo metamorphosis, transforming into adult gnats. They mate, produce eggs and after about five days they die and the cycle begins again.