DELL RAPIDS, S.D. (KELO) — As the sun went down and the lights turned on at this baseball game in Dell Rapids, a large swarm of Mayflies came out to play.

Paul Johnson, a professor of Entomology at SDSU has been ‘chasing bugs’ for 50 years and says while the swarms can be a nuisance, Mayflies are a vital resource for water supplies.

“The bulk of their lifecycle is in the water, where the immature stages feed on algae, diatoms, aquatic plants, and a lot of that bacteria, fungi and other stuff people call scum,” Johnson said.

Mayflies spend years developing in the water. While they grow into adulthood they act as natural filter feeders and keep water sources clean.

“A lot of the water quality studies that are done for pollution, erosion, whatever it might be, will often use Mayfly immature’s as indicators of quality of the water,” Johnson said.

Adult Mayflies live a short lifespan of one to two days and that time is spent mating.

“When they are mature and ready to mate, they swim to the surface, break the surface, the adult Mayfly comes out, rests for a bit on the water and then flies off,” Johnson said.

Though seeing these swarms can seem intimidating, Mayflies are very gentle and do not require the use of pesticides.

“We’re looking at a short term phenomenon in terms of their swarming. They are not poisonous they are not toxic, they don’t bite and they feed other organisms,” Johnson said.

As for why these adults are flying around a baseball field…

“These species are attracted to the lights which sort of brings this odd mixture of them being attracted to the lights at the same time they are trying to find mates,” Johnson said.

Mayflies are also a vital food source for birds, fish and bats.