Leafcutter Bee – In Mortar
Q: I have insects that are boring pencil-sized circular holes in the mortar where two brick walls meet. They appear to have a striped abdomen and they plug the holes with green leaf matter. How do I prevent them from doing it?
A: You are seeing the handiwork of leafcutter bees. They are solitary insects which typically use existing holes in which to lay their eggs. In the fruit orchards of New York and in the alfalfa fields of the Pacific Northwest farmers distribute thousands of blocks of wood having pre-drilled holes to attract these beneficial pollinators.
Farmers and gardeners in Georgia are beginning to appreciate the pollinating skills of several species of solitary bee. Our native honeybee population is almost wiped out due to destructive mites. The orchard mason bee, the leafcutter bee and the blueberry bee now help us get locally produced fruit.
Leafcutter bees do not bore into wood like the much larger carpenter bee. It is possible that the holes you see were made by a mason bee and are now being used by a leafcutter bee. They are not aggressive insects and on the whole are quite beneficial. I would either leave them alone or simply fill the hole with caulk.