It may be late June, but the mayflies stormed a bridge in Havana and blanketed the pavement so thoroughly that cops say travel across it has become treacherous.
"At one point they had piled 6 inches high and when ran over, became very slick," the Havana Police Department wrote on Facebook along with photos of the squirm-inducing swarm.
According to police, multiple motorcycle accidents were caused by the sludge left over when the carpet of bugs was run over by passing vehicles.
A Havana Police post also said cars at one point became stuck in the middle of the bridge and cautioned area motorists to cross with caution.
The City of Havana Street Department and the Illinois Department of Transportation are working in tandem to clean up the bugs.
Mayflies are extremely short-lived insects that start their lives in the water then mature into flying adults with a lifespan as short as a half hour.
While their mass hatch events can cause havoc, mayflies do not harm humans and are a vital part of the Mississippi River's ecosystem.
Mayflies are also an important indicator of pollution because they can only thrive in very clean water.