Fungus gnats

Appearing around the drain of my bathroom sink on Friday, a small swarm of tiny black flies, which fled from my investigations by running, rather than flying, away. Ah, fungus gnats — usually found in soil, as around houseplants, rather than in household drains, but there probably was organic material in the trap for them to feed on.

A shot of bleach, followed by flushing with hot water, cleaned up the infestation.

Another chapter in the annals of household insect pests, in the tradition of my 6/1/16 posting on drain flies and fruit flies and my 7/24/17 posting on, among other things, clothes moths.

From Wikipedia:

Fungus gnats are small, dark, short-lived gnats, of the families Sciaridae, Diadocidiidae, Ditomyiidae, Keroplatidae, Bolitophilidae, and Mycetophilidae (order Diptera); they comprise 6 of the 7 families placed in the superfamily Sciaroidea.

The larvae of most species feed on fungi, decaying plant material, or plant roots, helping in the decomposition of organic matter; some species are predatory. The adults are 2–8 millimetres (0.079–0.315 in) long, and are occasionally pollinators of plants and carriers of mushroom spores. They also may carry [plant] diseases such as pythium (which causes “damping-off” to kill seedlings) on their feet.

Most fungus gnats are weak fliers, and can often be seen walking rapidly over plants and soil, rather than flying. However when airborne, the gnats may be quite annoying to humans by flying into their faces, eyes, and noses, both indoors and outdoors. These flies are sometimes confused with drain flies.

My bathroom fungus gnats were indeed tiny, only a few mm long, and they were definitely walkers rather than fliers. They recalled to me the fungus gnats that used to afflict our houseplants in Columbus OH.

Getting rid of them around houseplants is fairly tricky. Bleach and scalding hot water obviously won’t do on plants, so various organic controls are called for.

I have only one indoor houseplant, a mini phalaenopsis orchid, and it’s free of fungus gnats — its soil is too dry for them — so the bathroom gnats must have come in from outside. Not unlikely, since there are plants in containers on both my patios and by my front door, and people go in and out all the time.

The term gnat. The compound fungus gnat has a specialized semantic relation between its parts: fungus gnats — well, actually, their larvae — feed on fungi, among other things.

Is the compound subsective? That is, are fungus gnats gnats? Well, maybe yes, maybe no, because gnathood is not an entirely clear concept. From Wikipedia:

A gnat is any of many species of tiny flying insects in the Dipterid suborder Nematocera, especially those in the families Mycetophilidae, Anisopodidae and Sciaridae. They can be both biting and non-biting. Most often they fly in large numbers called clouds. “Gnat” is a loose descriptive category rather than a phylogenetic or other technical term, so there is no scientific consensus on what constitutes a gnat.

University of Kentucky entomologists consider only non-biting flies to be gnats, while the Institute of Agriculture and Natural Resources of the University of Nebraska–Lincoln classify fungus gnats in addition to non-biting flies as gnats. Certain universities also distinguish eye gnats: the Smithsonian Institution describes them as “non-biting flies, no bigger than a few grains of salt, … attracted to fluids secreted by your eyes” [ick — but then we live in a world that also has eyelash mites in it].

Even if scientists fixed on some sharp definition of gnat (as they seem to have done for the gardener’s term fungus gnat), the ordinary-language term gnat would, like ordinary-language terms in general, still have unclear boundaries.

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