Cool summer nights, grilling steaks and dining alfresco are some of the joys of summers in Colorado. But wait, what are those nasty insects walking all over my steak, dipping into my wine and swarming around my guests, causing us to take cover inside? They are Western yellowjacket wasps.
Western yellowjackets are social wasps. Social wasps include yellowjackets, Western yellowjackets, hornets and paper wasps. They are colony-producing and make their nests of paper. You will see hornet and paper wasp nests in trees, shrubs and under building eaves. They are usually non- aggressive unless trapped or their nest is disturbed, and they are beneficial in their activities as predators of pest insects and as pollinators.
Yellowjackets nest underground using existing hollows or, occasionally, nest in dark enclosed areas of a building such as a crawl space, and will aggressively defend their nest.
The Western yellowjackets have a natural diet of insects and nectar but are opportunistic scavengers of protein, dead insects, garbage, meat, sweet foods and sugary drinks.
The Western yellowjacket is the most important stinging insect in Western North America. When people say they’ve been stung by a bee in Colorado, they most often have been stung by a Western yellowjacket, not a bee. Yellowjackets likely cause 90% or more of “bee stings.” When bees sting, they leave a barbed stinger behind, and the bee dies. Wasps, on the other hand, have a smooth stinger that retracts and can be used more than once.
So, what are we to do? There are traps you can use baited with the chemical heptyl butyrate that will only attract Western yellowjackets and prairie yellowjackets. Putting them out at the right time can greatly reduce the Western yellowjacket population.
When winter comes, nests are abandoned and never used again. The only yellowjackets to survive winter are fertile female queens that develop late in the year and find shelter to hibernate during the winter.
In spring, they emerge and begin foraging for nesting material and protein, usually in late April and throughout May. If a queen is not captured in early spring, she will find an in-ground cavity, build a new nest, lay eggs and feed the first larvae until a colony of worker wasps and drones is established.
April is the most important time to set out the traps. For every queen trapped in early spring, one entire colony is eliminated which otherwise can produce 200-plus Western yellowjackets by September. If you can find the entrance to an underground nest, a repeated nighttime application of an insecticide, such as permethrin, can eventually eliminate a colony. It will take persistence, especially late in the season.