Toulouse: long live the ephemera! Why the swarms of white bugs that have invaded the city are good news
This summer on the bridges, at the top of the lampposts, a strange phenomenon of swarms of insects intrigues observers. One you who explains are the ephemera.
Lit by streetlamps under the midnight sky, the Garonne is white. An opaque veil is deposited on its surface. A few meters higher, the lampposts are stormed by an impressive cloud of thousands of tiny butterflies. These are the mayflies. And when day breaks, all that remains is a carpet of cream-colored insects on the sidewalks and asphalt, like a shroud of dust…
With light pollution, the massive swarming of mayflies on summer nights along the banks of waterways becomes dramatic. Females fly up to artificial lights. Some of them land on the asphalt road to lay eggs, while the others join the swarm of several thousand individuals around the lampposts.
Outbreak in the middle of a heat wave
The shortness of life of mayflies, from a few hours to a few days depending on the species, is the origin of the name given to this group of insects, but their strong presence in the heart of Toulouse and its surroundings is a good omen!
Mayflies are very good indicators of the quality of aquatic environments and their populations are monitored. Since the larvae are aquatic, they are fragile in the face of organic-type pollution, or the rise in temperature, which decreases the dissolved oxygen content. Some species are particularly sensitive to it, others are more tolerant, but what is certain is that mayflies are generally among the first living beings to disappear when environmental conditions are modified by pollution. Their strong presence currently in urban areas and on the many bridges of the Garonne in the department is therefore a good sign.
turn off the lights
According to the head of naturalist missions at the Conservatoire d’Espaces Naturels d’Occitanie, Baptiste Charlot, “the species is at the base of the food chain. It serves as prey for other species, such as dragonflies, bats and birds.” Between the butterfly and the dragonfly, this little insect has been swarming around water points since the beginning of summer. And for good reason ! All climatic conditions are conducive to its emergence; the aquatic larvae were able to spend the winter, which was relatively mild, before hatching in the middle of a heat wave. Summer being hot, the small birds, like the butterflies, flock together, thus giving a spectacle as unique as it is astonishing. Their body size varies and can range from 3 to 35 mm depending on the species.
When houses are attacked, it is advisable to turn off the lights or close the windows of the lit rooms so as not to be invaded, although the mayflies are completely harmless. And remember, only for one night.