Some of the best nest plugs in the bug business are made of sticky plant sap–as it dries, it hardens into a protective door and can stand on its own or be topped off with debris. Today we’ll cover two insects that nest early in the year and use resin to do it.
The first are wasps from the genus Passaloecus, also called Aphid Wasps because they collect aphids to feed to their offspring. These wasps are shiny black with pale markings on their mandibles, the basal segments of their antennae and on their front legs. Boulder County hosts several species that range in size from just over 1/4 inch to 3/4 inch in length. Watch your boxes carefully and see if you can see them bringing home the bacon (er…aphids) for their babies.
Construction starts as a ring of resin all around the entrance but without a middle section so the mother can get in and out. Once her nest is completely provisioned, she’ll fill in the center and seal it off. Their nest plugs start off tacky then typically dry to a clear or white color. Often they’ll add debris as a finishing touch, but not always. Frequently Passaloecus wasps will nest in small tunnels, but depending on the specific species and number of nests in the block, they can choose medium sized or even large tunnels too.
If your block has Aphid Wasps, you’ll get very familiar with them–blocks that have any often have many. It’s unusual to find only 1 or 2 nests and much more common to find 5, 10 or even 15 nests.
The second “bug” for our Resin Plugs are small bees, about 3/8 inch long, in the genus Heriades. These are members of the leaf-cutting bee family, and their bodies are elongate, heavily textured, with white hair bands on abdomen.
You’ll be able to tell Heriades plugs from Passaloecus plugs because the bees’ handiwork tends to be created from a darker resin placed flush with the face of the bee block. Their plugs also have a shiny or glassy texture, not a tacky one, and may be topped with one to three pieces of pebble or wood chips. As the summer progresses and the sun gets hot, any plugs facing south may melt and become gummy, loosing their luster, and sloughing off any debris in the process. Starting in the early summer, you’ll see these nests appearing in smaller hole sizes, particularly in the 1/8″ holes. While Passaloecus wasps tend to congregate, Heriades bees don’t group as much, so you’ll rarely see more than 2 or 3 nests made by these bees in the same block.
We will revisit Resin Plugs again as we get closer to fall, but until then, keep your eyes peeled for these interesting bees and wasps, and enjoy both the beauty of the insects themselves and the nests they make.