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This season: Iowa wasp populations rise in late summer

They're here, and they'll stay until fall

Wasp nests are seen along the eaves of a condo building in southeast Cedar Rapids on Tuesday, Aug. 2, 2016. (Liz Martin/The Gazette)
Wasp nests are seen along the eaves of a condo building in southeast Cedar Rapids on Tuesday, Aug. 2, 2016. (Liz Martin/The Gazette)

CEDAR RAPIDS — August means a lot of things.

The Iowa State Fair. Getting the kids ready to go back to school. One last get away before the end of the vacation season.

It also means it’s time for the spike in the wasp, yellow jacket and hornet population.

Donald Lewis, a professor in Iowa State University’s Department of Entomology, said wasp season starts in early May and increases during the summer months.

“A single queen will build to dozens or hundreds of wasps by the end of the summer, per colony,” Lewis said. “We’re in that increase ... . That’s what people are seeing. They’re seeing the workers out doing what needs to be done, collecting other insects from landscape and the garden to feed the offspring.”

Lewis said a fairly mild winter and a dry June probably could have contributed to an even greater wasp population this year, though no official wasp census has been done in 2016.

Wasp colonies start as a mated female alone in the winter after the rest of the colony has died off. The queen then lays her eggs, which hatch and become the workers.

Lewis said the dry June helped the wasp population because the workers were more successful gathering building materials for the nests and food for the offspring.

Lewis noted that just because you may not being seeing wasps in your home doesn’t mean they’re not around.


“Inspect populations vary so greatly from place to place, in addition from year to year,” he said. “Depending on your location, you can have the exact opposite of someone who is nearby.”

So what good is a wasp anyway? They sting and they don’t pollinate as bees do. Lewis said wasps don’t get much credit because views of their usefulness are generally “human-centered.” They do, however, play a role.

“As a predator, they have a benefit to us,” he said, noting wasps will take the caterpillars and other bugs that feast on gardens, “cut them up into sushi” and feed them to the queen’s offspring.

They’re also a link in the food chain, though there’s not much that eats wasps, Lewis added.

A species of wasp that is relatively new to Iowa — it was first reported in 2012 — may be a little too good at its predator role, however. In an article published for Iowa State last July, Lewis said the European Paper Wasp has contributed to the decline of butterfly populations in some areas.

It also has displaced some native species of wasps due to its reproduction rate.

Regardless of the species of wasp, Lewis said we can expect them to hang around a little while longer.

“Most of the wasps will be here until it freezes,” he said. “When we get into September, wasp populations start to decline because the workers are dying of old age. The ones that are alive will perish with freezing temperatures by Thanksgiving.”



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