Our Eastern Carpenter Bee (Xylocopa virginica, family Apidae) is a Dr. Jekyll and Mr. Hyde insect. The bee’s Jekyll side is on display as it visits flowers to gather nectar and pollen to feed its young. These large, docile bees are significant pollinators.
The bee’s Mr. Hyde side is on display when carpenter bee females (Mrs. Hyde?) bore large, branching tunnels into wood decking, siding, fencing, etc., where the damage may weaken the structural integrity of the wood. The images below show such damage. I’ve also included a photo of carpenter bee tunnels in a dead white pine branch which demonstrates what the bees used before we provided nice structures for them.
The carpenter bee’s Mr. Hyde side is also revealed when males buzz anything that comes into close proximity to their perceived harem including homeowners. Although it’s a ruse because they can’t sting (they lack ovipositors (= stingers)), their aggressive flight plans which commonly include hovering at eye level can be unnerving.
The Tiger Bee Fly (Xenox tigrinus (previously Anthrax tigrinus)) belongs to the family, Bombyliidae, with members commonly called “bee flies” because they bear a striking resemblance to bees. That explains the “bee” in the tiger bee fly common name. The “tiger” comes from the intricate black markings on the fly’s wings.
The adults of many species of bee flies feed on nectar and pollen with some being important plant pollinators. Tiger bee flies are no exception. The adults are commonly found hovering around flowers.
The larval stages of bee flies are predators or parasitoids feasting on the eggs and larvae of other insects. The larvae of tiger bee flies feast as parasitoids on carpenter bee larvae. Parasitoids are parasites that kill their hosts.
Tiger bee fly females lay their eggs near carpenter bee entrance holes. The resulting larvae (maggots) crawl into the carpenter bee’s tunnels and first feed on the pollen balls intended for the carpenter bee’s larvae. It’s the ultimate insult. First, the maggots eat the bee larvae’s lunch and then the bee larvae!
However, they don’t consume the bee larvae outright. Each maggot attaches itself to the outside of an early instar bee larva and begins sucking out the essence-of-insect, like a tiny vampire. As the carpenter bee larva matures, so does the attached tiger bee fly maggot. The carpenter bee larva is slowly converted into a dried, wrinkled husk while the bee fly maggot is converted into a big, plump maggot that pupates.
I could not find information on the overall impact that tiger bee flies have on carpenter bee populations. However, the authors of the scientific paper cited in “Selected References” below note that the tiger bee fly females may lay 2,000 to 3,000 eggs. Although they also note that while most eggs are laid near carpenter bee entrance holes, some eggs are laid away from the entrance holes. Presumably, all the fly maggots don’t find their way to a bee larva.