Question
We live in Alberta, Canada and the last few summers we've noticed our oak tree in our backyard being constantly swarmed by wasps & hornets. There are no visible signs of any nests and since it's both insects we believe they are feeding off of something in the tree. A friend of my daughter just got stung and it's like they are taking over that area of our yard. Any info on why they are doing this? Is there anything we can do?Thank you

Answer
Sometimes wasps feed on a substance that an insect called aphids produce. If the leaves and under the tree is sticky this is a sign that aphids are present . They excrete a sugar based substance called honeydew which the wasps are feeding on. The other reason associated with the tree is an oozing of liquid from the trunk of the tree called wetwood or slime flux. This is a pressure build up inside the tree caused by bacteria that forces the liquid out. Wasps feed on the slime flux. The aphids can be controlled with an insecticide spray but all the leaves will have to be sprayed and on a large tree is  a large job. There are insecticides that can be put on the ground and watered in check with your local nursery about these IF the sticky is present.

The slime flux can not be controlled and will go away on its own. If you see the liquid on the trunk bark you can spray the area with one of the wasp sprays and this will discourage the wasps from coming.