Earlier this year I wrote about the annual emergence of Lake Flies in Wisconsin. But wait, there's more! More insects, that is. This week Wisconsin-ites were treated to a mayfly emergence. Just how many mayflies are there? Enough that they show up on weather radar:

"The Mississippi River produced a massive radar echo as mayflies emerged from the water and became airborne. The mayflies were detectable on radar around 8:45 pm...The radar loop below shows the reflected radar energy (reflectivity) from 8:35 pm to just after midnight. The higher the values (greens to yellows) indicate greater concentrations of flies."

July 20th, 2014: Night of the Mayflies. National Weather Service/NOAA

Because they coat surfaces in an epic biblical plague, mayflies sometimes cause highway accidents. The slippery goo created by millions of mayflies is blamed in a three-car pileup in Hager City, WI yesterday night. A major emergence in 2012 resulted in snow plows being called out to clean up the mess.

Adult mayflies are basically gonads with wings. They don't eat; some species don't even have working mouthparts. They are not interested in your puny roads and ATM money machines, humans. They need to get busy gettin' it on in a massive mayfly orgy. (Also, male mayflies have two penises. I thought you'd want to know.)

The mayfly species emerging this week lives only one night as an adult. They mate, the male dies after ejaculation, and the female feebly flutters off to lay her eggs. The name for this group of insects is Ephemeroptera, from the Greek word for “short-lived” or “ephemeral”.

Why do mayflies emerge en masse?

It's not actually a "live fast, die young in a blaze of sexual glory" story. Mayflies spend the majority of their life underwater, quietly eating algae and plant material. The full growth cycle of a mayfly can take up to 4 years; we just notice them when they pile up in post-coital exhaustion.

Mayflies emerge synchronously around dusk to avoid their main above-water predators: birds and bats. Predators trying to capitalize on a sudden mayfly all-you-can-eat buffet are overwhelmed by the emergence of millions of insects. Some individuals make it through, and the species continues.

Mayfly larvae are delightfully called "naiads," and provide critical food for fish. The bodies of immature mayflies have beautiful external gills; this is also why they are important in assessing water quality. Mucky, polluted water is not a place a mayfly larva can breathe. Detroit has had mass mayfly emergences in the past, but a toxic algal bloom in Lake Erie this year is damaging populations of all the animals in the watershed.

This video shows the last minute of a female mayfly's life; she flops on the water in exhaustion and dumps a massive load of eggs into the water. Within seconds, her eggs hatch and the naiads begin to swim.

Mayflies are some of the most ancient insects around; they are well represented in Carboniferous fossils dating >300 million years ago. Fossil mayflies look remarkably like our modern mayflies; some consider them "living fossils." The oldest fossil of a winged insect is a mayfly.

This dance of death and birth has been going on for a long time; try to focus on the wonder, rather than the gross out. The protein in mayfly bodies may have powered the rise of the reptiles. We can share some space for a few days.

Homepage image: Richard Bartz via Wikimedia Commons