Willow Galls

Day 292: Red galls can be found on almost any species of Salix (Willow) in the Pacific Northwest. These growths form around the larvae of specific insects (wasps, midges, etc) and arise as a reaction to chemicals secreted by the insect itself. The gall serves as both protection and as a confined source of food for the single developing larva contained within its shell until the insect is ready to emerge. In this instance, the responsible party is likely a member of Pontania, i.e., a Sawfly. Several members of the genus are specific to one particular host species, although some willows can be affected by more than one species of Pontania. Galls generally do not damage the tree, although the same cannot be said for the mature bug.