As winter-numbed Minnesotans swarm parks, gardens and back yards to celebrate the tardy arrival of warm weather, they are running into an unwelcome sign of summer: wasps.

While wasp numbers aren’t unusual for this time of year, experts say they’re getting plenty of calls, perhaps because we’re just emerging from so many bug-free months.

“We’re so accustomed to cold weather, when we get warmth and see things flying around, it’s almost like we’re not ready for it,” said Jeff Hahn, entomologist with the University of Minnesota Extension.

Extension and pest control services have gotten reports of wasps in homes this spring. Hahn said one call involved a “few dozen” wasps that were clustering on window screens, apparently after they overwintered in walls or cracks in the home.

The only wasps that overwinter are the queens. In this case, Hahn said, paper wasp queens overwintered in a group somewhere under siding or in walls.

Todd Leyse, president of Adam’s Pest Control in Minneapolis, said the phones began ringing and “things began to pop” when the temperature hit 80 degrees.

“It’s kind of out of the ordinary; everything is later this year,” he said.

People who call now about wasps in homes are worried that the insects are building nests inside, but they’re not, Leyse said.

He recently visited a house with wasps in the basement. “There was no nest,” he said. “They were all very sad, skinny-looking wasps that had tried to survive in the siding.”

Beneficial, but they sting

Paper wasps and yellow jackets are the most common gregarious wasps in the metro area, Hahn said. Right now, the queens are building small nests to lay their eggs. Later, the queen will rest and the workers will do the building.

“Once they get going, they’re kind of industrious,” Hahn said.

Hahn said wasps are considered beneficial insects because they eat a lot of “bad” bugs, including caterpillars and flies. “But they have a darker side, too, because they will sting to defend themselves,” he said.

He suggests leaving nests alone if they are high on a house or tree, but said now is the ideal time to remove nests near doors or areas where people or pets will be this summer.

People “should not ignore it if it is nearby,” he said.

If a nest is out in the open, Hahn suggests buying an insecticide that is labeled for wasps and hornets, waiting until evening when the insects have returned to their nest and spraying it directly.

Leyse recommended that people hire a professional if they think wasps are nesting in walls. Poorly applied insecticide at a spot where wasps are entering a house will make the insects look for another way out, including chewing right through Sheetrock to escape to the interior of a home.

Hornets especially will do this, “and they will go after people,” Leyse said.

If you suspect wasps are building in a wall, Leyse suggests standing by the side of the wall of the house to watch where wasps are going. Do this on a warm day when the insects are active.

“Watch and see if they’re coming and going from the house; they will fly straight back to an opening,” he said. “That’s why they call it a beeline.”

At this time of year, Leyse said, the queens are scouting for nest sites, bobbing in the air along walls, eaves or tree branches looking for a site to build. Serious nest building happens in June and July.

But Leyse doesn’t fault people who get excited when they see wasps.

“If people have allergies, they probably freak for a good reason,” he said. “If they don’t have allergies, most people freak when they’re around a stinging insect.”

Wasps, he said, are “kind of a pain, literally.”