Honey Bee Biology
Honey Bee Biology - August 2014
Late Summer: When Beekeepers get Questions on
Yellow Jackets and Hornets
by Dr. Wyatt A. Mangum
As beekeepers we get questions from the public on various stinging insects, not just honey bees. Typical concerns include bumblebees, carpenter bees, and ground nesting bees. Then, there are the paper wasps building exposed horizontal nests under the corners of windows, doors and other sheltered places. Yellow jackets and hornets cause much anxiety too. With the arrival of late summer, when yellow jacket and hornet populations peak, this article concentrates on their biology, giving beekeepers, especially new beekeepers, some information to help answer questions they might get from people who typically begin by telling their stinging stories.
Most laypeople, which can include news reporters, confuse the terms bees and wasps, using the words as if the insects were the same. They are not. Without going into the strict taxonomy, which involves numerous technical terms, here are working definitions of the two: most bees live on nectar, honey and pollen. Most wasps feed (chewed) meat, usually other insects, to their larvae. I say most for each group because nature has made notable and fascinating exceptions.
In the tropics, some stingless bees (in the genus Trigona) consume the flesh of dead animals, usually small frogs and lizards, although larger dead animals are welcomed treats on their necrophagic menu. It is thought these bees deposit digestive enzymes on the flesh of the dead. Then, bees consume the resulting liquid slurry of protein, holding it in their crops like nectar, while flying back to their colony. Necrophagic Trigona from different colonies even fight over the dead, upon meeting on a rotting animal, a competition for food (Roubik, 1989). While these bees have a wasp-like diet, what about the other way around? Wasps with a bee diet.
Scattered across some locations in the hotter and drier regions of the world, a group of wasps, the pollen wasps (in the subfamily Masarinae) feed their larvae nectar and pollen, not flesh. Pollen wasps do not hunt insects like carnivorous wasps, thus showing a behavioral change in the adults in addition to their different larval diet. For a nest, typically a pollen wasp digs a tunnel in the ground (apparently similar to other ground-nesting bees and wasps). The mother wasp provisions her nest by carrying a nectar and pollen mixture in her crop – internally instead of externally in pollen “baskets.” That transport method is not surprising. In the general study of all bees (Melittology), some 20,000 species of bees, the two main ways to carry pollen are internally and externally. Beekeepers focus on the latter since honey bees carry pollen externally on their hind legs. Pollen wasps have evolved to the former – an internal pollen transport, the same method used by some bees. Typically, these solitary bees are almost hairless, far from fuzzy, like wasps including pollen wasps. Being virtually hairless and carrying pollen internally is well within the realm of the bee world, even when done by a wasp, a pollen wasp.
Another key difference between bees and wasps is that wasps and hornets use paper for nest construction. For honey bees, they use wax. (Other bees use a variety of materials, bits of leaves, tree resin, etc. But they are rarely involved in a stinging incident and are essentially harmless.) In many situations, the nest is not visible and the material is unknown. So one needs to listen for other evidence as a person tells of a stinging incident, usually seeking the culprit. One is the sudden appearance of the insects late in summer.
Late summer stinging incidents with yellow jackets, or others with hidden nests, provoke dismay that the nest appeared there suddenly, say yellow jackets coming out of the grass in a spot mowed all season. Why now? Unlike honey bees that winter intact as a family unit, a colony of yellow jackets (also hornets and wasps) all perish except for the mated females, the “queens,” which hibernate (at least in my area, and might not be true further south). A queen yellow jacket, specifically one individual, starts the nest in the spring. She rears a small clutch of workers, which in turn rear more. With a small number of worker yellow jackets, they do not tend to launch a big stinging defense of their nest earlier in the season. But here is the key point – they are there, just not noticeable.
Early in the spring, I see queen yellow jackets hunting for nest sites. I watch them flying a few inches from the ground. Their slow flight, large size, and yellow and black stripes make them easy to spot against the drab ground. Usually a queen yellow jacket selects a nest site in a protected place, for example, a small underground burrow initially dug by a mouse or other small animal. On the other hand, I have also seen them nest in walls. Figure 1 shows a small nest started by a queen, a rare find. Including the paper envelope, the nest is about the size of a quarter. Inside is a small bit of paper comb of just a few cells. Unlike queen honey bees, specialized for egg laying, a queen yellow jacket can forage, defend the nest, feed larvae, and chew wood fibers to make paper for a nest.
While the queen picks a small burrow, the yellow jacket nest can grow as large as a basketball. The yellow jacket workers enlarge the underground cavity by removing small pieces of dirt. If you look closely at a large colony with numerous workers flying out, some of them carry bits of dirt in their mandibles (jaws). By late in the summer the colony population is large enough so the wasps can aggressively defend their nest. Now the colony will not tolerate the vibration of the lawnmower. Conditions are ripe for a stinging incident.
To see the extent of a yellow jacket nest, I dug one using only ...