Wasps can live in a variety of environments, including in trees. Some types of wasps visit trees for honeydew, while others actually make live in trees. People find wasps disturbing because they can sting or bite humans. Wasp stings and bites are usually painful but not dangerous; however, they can seriously endanger people with wasp allergies.
If a tree owner sees wasps around a tree, he should look for a nest before assuming that wasps actually live in the tree. Many wasps simply visit trees to look for honeydew, a sweet substance that aphids, mealybugs, soft scales, whiteflies and other plant-sucking insects produce.
Yellow jackets are a type of wasp that usually nest in the ground, although they can build nests in trees. Paper wasps build nests that hang underneath horizontal surfaces, including underneath tree branches. Wasps can also live inside hollow trees. Eurasian wood wasps damage trees by laying eggs inside them and by depositing a fungus that kills trees so the wasps can live more easily inside the tree.
Some types of wasps, including oak apple gall wasps and Oriental chestnut gall wasps, cause trees to form galls with wasp larvae inside. Mild gall wasp infestations usually do not harm trees much, but severe infestations can cause serious problems ranging from early defoliation in the fall to suppressed growth and even death.
Since several types of wasps like to make nests in hollow trees, homeowners with wasp allergies might want to deter wasps by getting rid of trees with large hollows or by spraying holes in trees with a wasp insecticide. Avoid purchasing tree seedlings that have visible round growths (galls) on them. Wasp experts at the University of Missouri Extension recommend pruning and burning infested tree limbs to get rid of oriental chestnut gall wasps. To prevent Eurasian wood wasps, keep trees, especially pine trees, as healthy as possible by planting them in the correct environment and providing them with enough water. Eurasian wood wasps tend to lay eggs in stressed trees, and keeping trees healthy can help prevent the wasps.
Tree owners do not need to remove wasp nests if the wasps are not bothering anyone. Removing wasp nests can be dangerous, especially for people with wasp allergies or if nests are high up in trees. Tree owners may want to hire professionals to remove nests. To get rid of a nest without the help of a professional, Cornell University recommends spraying the exposed nest or inside the tree hole with a wasp spray during the evening and during temperatures below 60 degrees Fahrenheit. It is safer to spray wasps in cool temperatures because the wasps are not as active when cold. The University of Minnesota Extension recommends removing wasps in June.