Every year around this time, we can expect a sudden eruption of clouds of mayflies to emerge, as Gwen Pearson describes. There have been a few times I’ve been out driving when caught in it, and the car gets coated with brown dead bug smears, to the point where visibility is a serious problem.
But she also shows a video I found even more terrifying: this is a dying mayfly floating on the water, and she constantly dribbles out eggs, making a big pool of them on the bottom. And then one minute in, they start hatching!
Now I study an animal which develops very rapidly, the zebrafish, but this was shocking — you mean they go on a mating flight, drop to the water, and spew out eggs that develop into larval hatchlings in minutes? Impossible! Laws of thermodynamics! Cellular interactions and pattern forming mechanisms! The biochemistry couldn’t go that fast! Cell cycle times must be in milliseconds! Inconceivable! My brain is melting!
Fortunately, I read more closely.
Most mayflies lay their eggs immediately after mating; the eggs then take anywhere from 10 days to many months to hatch. Cloeon cognatum is an exception. This species is ovoviviparous, which means that a mated female holds her eggs internally until embryonic development is complete (about 18 days), after which she lays them in water and they hatch immediately. This female was dropped onto the water surface moments before the video started.
Whew. That’s better. And 18 day development time? Easy peasy. I guess I don’t have to hover around the margins of local lakes trying to catch a few minutes of development, once a year, after all.
By the way, here’s a photo of my car from last year, when I got caught driving by Lake Minnewaska one night: