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Wild Side: What's Bugging You!

Some biting gnats next to a dime. (River Falls Journal photo by Dan Wilcox)

It’s hard to ignore the swarm of small insects buzzing around your head when outside these days. Not only do they distract and aggravate but some of them bite. They seem to focus on ears and the zone just beneath hat bands. I think they are worse than mosquitoes.

--By Dan Wilcox, outdoor columnist

The pesky buggers are Dipterans of the family Simuliidae; two-winged tiny insects called biting gnats, buffalo gnats, black flies and many other unprintable names. There are about 30 species of them in this region. Some don’t feed on humans and just buzz around. Others have slashing mouthparts and draw blood to obtain nutrients to help them produce eggs. The biting flies inject an anticoagulant into the wound which makes for painful, itchy bites. Up north where black flies are really abundant, they can drive people crazy and force loons and black bears to dive into the water.

Black fly larvae live in cool or cold well-oxygenated streams. The larvae attach to wood or rock and filter out fine particulate matter to eat. They live as larvae for about a month, enter a pupal stage for a few days, and then float to the surface to emerge as adults.

The adults live for a few weeks, mate, and lay their eggs on or just above the water. Several generations can grow each summer. We’ve had over 10 inches of rain in June and nearly three inches of rain so far in July, providing plenty of flowing water for the gnat larvae to grow in. There are lots of them this year probably due to all the rain. I’ve been surprised to find swarms of gnats on hilltops far from flowing water but they are especially abundant near streams and rivers.

Around the Twin Cities, the mosquito control people treat streams with the natural product, Bacillus thuringiensis var. israeliensis (Bti) to kill black fly larvae but the high flows this year have rendered that ineffective. We may have fewer gnats around our place due to the squadrons of dragonflies and bats flying around dining on them in the evening.

I’ve found that insect repellents with plant-based oils like geraniol, citronella and vanilla are pretty effective against gnats. Insect repellants with DEET seem to attract them but do fend off mosquitoes and ticks.

Horse owners put covers over their steed’s ears and foreheads to keep the gnats from biting them. When fishing on the Kinnickinnic and Rush Rivers recently, between the awful muddy runoff events, I’ve learned to live with the swarm of gnats buzzing around my head and appreciate the fact that the trout and other fish are feeding on their larvae.

Hopefully we will get a spell of dry weather that will reduce the abundance of gnats. Despite the nuisance they cause, it’s a good sign that the rivers around here are clean, cold, and well-oxygenated enough to support them.     

Please send any comments and suggestions for this column to me at