WATERLOO - The swarms of gnat-like bugs hovering in parks and backyards this spring likely originate from an old foe - last year's floods.

Iowa State University entomology professor Ken Holscher said the unusually high number of black flies buzzing about in 2009 hatched from tiny eggs laid in running water a year ago.

Holscher said heavy rain may have kept small creeks flowing for most of last summer and into this year. No one tracks black fly populations in Iowa, so he has relied on anecdotal evidence from people calling to ask about the pesky "gnats" that bite.

Typically between early May and mid-June, he said, adult females need to feast on an animal's blood before they lay eggs.

"I've been here 27 years, and every now and then we'll have one of those years where we'll get a lot of calls," he said.

Jon McNamee, Black Hawk County environmental health program manager, said the county's use of larvicide - a chemical used in standing pools of water - helps control the mosquito population, and to some extent, black fly numbers.

Black fly bites can be painful, he said, but they do not carry disease.

"They're just a nuisance," he said.

The mosquito season has been normal, McNamee said. He expects it to be comparable to most of last year, when mosquito levels dropped off after flood waters dried. People should remember to empty bird baths and pools of water that might fill after rain to control mosquitoes, he said.

The state health department issued a reminder this week to look out for disease-carrying ticks. Cases of Lyme disease, a bacterial illness transmitted by deer ticks, have risen this decade. Last year, 105 cases were reported in Iowa.

Four cases have been discovered this year, including one in Black Hawk County, the local health department reported.

Symptoms of Lyme disease include fever, headache, fatigue and a skin rash often in the shape of a bull's-eye.

To avoid tick bites, experts recommend people stay out of tall grass, and check themselves thoroughly after venturing into heavily vegetated areas. Spraying long pants with repellent that includes DEET can help keep the critters away.