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October 28, 2015
By Bob Merz
Zoological Manager, Invertebrates
Then in a wailful choir the small gnats mourn
Among the river sallows, borne aloft
Or sinking as the light wind lives or dies...
-"To Autumn" by John Keats (1820)
I've been cycling to and from work for probably close to 30 years now. Usually not in the dead of winter, but most days during the rest of the year, I hop on the bike for a short commute.
It's nice. The routine slows me down. I tend to notice, even in a very urban environment, natural cycles. Weather patterns change from season to season. For instance, it's very noticeable the times of year that I mostly have a headwind or a tailwind. Daylight hours are another factor that I need to consider when riding, and those change drastically throughout my nine or so months of riding.
I also notice certain animal patterns. Certain bird species are more gregarious in the early spring; others are completely missing in the autumn. I notice when cicadas first start to call. And, I have been recently reminded of something that occurs a lot this time of year—something that many of you may have also probably noticed: annoying clouds of gnats!
You would think that after 30 years, I'd get better at cycling...but no. I still grimace up the same hills that I have grimaced up for decades. And this time of year, on those warmish days, with my teeth bared in the struggle, I get gnats in my teeth.
So, what's going on? Why the clouds of gnats on these warm autumn days?
First, let's start with the term "gnat." This term is a general one that isn't specific to any species. More often than not though, it refers to what are generally very many species of small flies—and there are well over 150,000 species of flies. However, in common usage, it can be really general and refer to any tiny flying insect, even very small wasps and bees. So that number grows drastically.
Because of all the species involved with the term "gnat," it is difficult to get too specific. But in general terms, what is happening now is that certain species of flies (tiny, little flies) have had their life cycles triggered by the first cold. In cold weather, they go dormant, and then later in warmth of certain days, gnats emerge and congregate.
What I find interesting about this behavior is that this "gathering" of gnats is usually very systematic. Many species will form these clouds near some discernible object. Either a dark object against a light background or a light object against a dark background. In fact, sometimes these clouds are given the nickname "ghosts" because of their slightly changing, see-through amorphous form. Seen in the right light, these clouds could trick your eyes.
And gnats form these clouds simply to breed. Think about it. When you are so tiny that a mate may have a next-to-impossible time finding you among vegetation, it makes sense to stand out. So, males gather in the clouds in a very prominent spot and hope to be noticed by females.
So now, knowing what I know, I'm slightly less annoyed when I ride through these clouds of gnats. It's just part of nature's cycle. In a week or so, it will be over, and I can continue grimacing up the hills in peace.