Mayflies seen on weather radar ~ and the shortening life !!

It was reported in US Press last July 2014 -  it was stated that at about 8:45 p.m. Sunday the National Weather Service picked up this rather beautiful radar event, in which what registers as “light-moderate rain” seems to emanate from the Mississippi River between Wisconsin and Iowa and into Minnesota.  It was not exactly a rain – it was a swarm of mayflies - gobs of mayflies; piles and piles of mayflies.  The swarm lasted for a few hours and by the time it was over many a windshield and wall was caked in slimy bug carcasses. The swarm was blamed for a three-car pileup in Wisconsin that left one person hospitalized.

They look somewhat similar to dragonflies that we have seen.  Mayflies are close relatives of Dragonflies and damselflies, but Mayflies are tinier, the antennas are large and at the tail has two or three long feelers.  Mayflies or shadflies are insects belonging to the order Ephemeroptera (from the Greek ephemeros = "short-lived") referring to the brief lifespan of adults.  They have been placed into an ancient group of insects termed the Palaeoptera, which also contains dragonflies and damselflies. They are aquatic insects whose immature stage usually lasts one year in fresh water. The adults are short-lived, from a few minutes to a few days, depending on the species. About 2,500 species are known worldwide, including about 630 species in North America.  The naiads live primarily in streams under rocks, decaying vegetation, or in the sediment.  Most species feed on algae or diatoms, but a few species are predatory.

Mayflies usually live for 24-72 hours; not counting the period of an year or more spent on the bottom of the lake as a nymph living burrowed in the mud. Within that three days, though, they manage to get into about everything one can imagine.  Many mayflies stack up on the streets below street lights.   Once on the street, they are usually run over by cars and make this "snapping" sound and it's all over.

In the US, the mayflies showed up on the weather radar as the equivalent of a light to moderate rain storm, according to the National Weather Service. As the service described it, “the Mississippi River produced a massive radar echo as mayflies emerged from the water and became airborne.  On that day, mayflies were swarming in La Crosse, La Crescent, Stoddard and points up and down the river. While the emergence of mayflies from their river bottom mud dwelling can occur at various times through the warm season depending on the species, this particular emergence was that of the larger black/brown Bilineata species. The radar loop  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.

As nymphs, these aquatic insects proceed through one or two years of larval development as filter feeders, consuming decaying organic matter at the river bottom. In summer, large numbers of nymphs synchronously emerge from the water at dusk and take flight as sub-adults. Within 36 hours of emergence, the sub-adults metamorphose into adults that subsequently swarm in the air to mate before returning to the water surface to lay their eggs and die. Some of these emergence events are so large and widespread that swarms can be detected by Doppler weather radar. Unfortunately, they’re attracted to lights, so they often head for lighted highways after they hatch. Millions of them get run over or squashed, leaving behind a green slime that’s so slippery it can cause accidents.

Already known for its brief adult existence—a mayfly commonly dies within hours of becoming airborne—the insect’s life cycle is being accelerated by rising temperatures, according to findings from a river immortalized by Izaak Walton in The Compleat Angler.  A five-year study on the River Dove in northern England found that Ephemera danica—a species known simply as the mayfly or green drake—is reaching maturity in one year instead of two. Average river temperatures in the Dove catchment area have risen about 1ºC in the past 20 years, while average summer river temperatures have climbed by one to two degrees Celsius, the researcher noted.  Everall suspects that warmer waters have triggered the mayfly growth spurt by speeding up the insects’ metabolism. “They’ll grow faster because they feed at a greater rate, and there’s often more food around at warmer temperatures in terms of algal growth and that kind of thing,” he said.  In addition, the rise in water temperature causes it completing their life cycle as early as they can; as a consequence, the adult mayflies have gotten noticeably smaller: Females are now on average eight to ten millimeters smaller than they were before 2008, Everall reported.

Steve Ormerod of Cardiff University’s School of Biosciences said the Dove findings are extremely interesting but are not easy to interpret, especially given the relatively short study period of five years.  “Mayflies are hugely important not only for fish but birds like grey wagtails almost certainly tie their breeding season to Ephemera danica [the birds’ busiest chick-feeding period appears timed to coincide with the mayfly hatch],” he said.  The River Dove study was prompted following reports from trout fishers that the mayflies they were matching their flies to were getting smaller.

Interesting indeed; Western researchers are not only  recognizing the importance of terrestrial landscapes but also are now inclined  at recognizing the importance of freshwaters in general. So much goes in to studying even the tiniest of insects and organisms.

With regards – S. Sampathkumar

27^th Mar 2015.