In southwest Ontario, in communities near the lake(s), we get an infestation of fishflies (also called mayflies and shadflies) in June. They have an interesting and short lifespan. When they emerge from underwater to procreate (their sole purpose), they create swarms in the hundreds of thousands. Wherever there is light at night (street lights, shop windows, houses, etc), they congregate and leave piles of dead carcasses on sidewalks and streets. They also smell. But they are harbingers of a healthy water system so should be more welcome than they are. The clean up is often done with hoses and shovels. It's a typical early summer event. (All pix from online, local postings)