This question and answer were provided by Purdue Extension: In the Grow.

Question: I have small evergreen trees planted in my yard. They are the small, slow-growing type. They are around eight years old. Every fall, the yellow jackets start swarming around them, crawling in and out of the inside of the tree. They don’t seem to hurt it, but it looks like they are trying to find something, acting like a honey bee on a flower. But these have no flowers. They don’t bother us as long as we don’t get too close. Could you tell me why this is happening? – C.K., Shoals, Indiana

Answer: Our Purdue entomologists advise that yellow jackets commonly scavenge for food in the fall, and it is likely they are attracted to tree resin or sap that has some sugar content. Scavenging yellow jackets are less aggressive than those that are protecting a nest. And you are correct; they will not harm the trees and will generally not attack unless provoked. We commend you for aiming for a peaceful coexistence!

View the full post at Purdue Extension’s: In the Grow website.

Resources
Social Bees and Wasps, The Education Store
Indiana Beekeepers Swarm List, Indiana DNR
Department of Entomology, Purdue University

Purdue Extension: In the Grow