Bees and wasps are easy to confuse, especially when a wasp is carrying a load of pollen. This beewolf feeds on bees, but smears pollen wherever he goes.
Inside: Beewolves are close relatives of bees. In fact, they are so close they are pretty good pollinators themselves.
Random acts of pollination
Who doesn’t love an enchanting mystery? As I peered through the viewfinder of my camera, I knew I was looking at something weird. Here was a solitary wasp with an abdominal scopa, or so it seemed.
This article first appeared in 2 Million Blossoms, January 2020, pp. 47-48.
A scopa is a dense patch of hairs that bees have on their bodies to help them collect pollen. The hairy patch holds the pollen grains in place as the bees fly from place to place. Many beekeepers have seen abdominal scopae on the underside of mason bees or leafcutter bees.
But wasps are meat-eaters that don’t have bellies bedecked with pollen-carrying hairs, so what was I seeing? Clueless, I snapped a few photos for a closer look.
A solitary, ground-nesting wasp
The creature in the portrait is a beewolf, a solitary, ground-nesting wasp that preys on bees. Although we often dismiss wasps as pollinators, the vast amount of pollen on this fellow’s abdomen tells a different tale. (Yes, it’s a male.)
Unlike a bee, a beewolf has absolutely no use for pollen and would never collect it deliberately. Instead, the plant—in this case a goldenrod—takes advantage of the wasp’s anatomy and gives him a load he doesn’t want.
Some female beewolves are so pollen-adverse they diligently remove and discard any pollen adhering to the bees they catch. Once the prey is clean, the female stores the ready-to-eat prey for her larval offspring to munch on. It seems the kids don’t like vegetables.
Brush-on pheromones mark his territory
This particular beewolf, Philanthus crabroniformis, lives in the western states and is especially fond of nectaring in Solidago species. After emergence, the male squeezes mandibular pheromones into two small hair brushes that protrude from the sides of his face.
Using the wetted brushes, he paints the pheromone on grass stems, the first step in marking his territory. Once that is done, he uses his much more massive abdominal brushes to smear the pheromone around and assure good coverage. He just wiggles his rear until the job is done.
As the male hunts for a mate in the flowers or pauses for sips of refreshing nectar, some of the pollen sticks to his abdominal brushes and gets transferred, quite by accident, to the female parts of another flower. By no design of his own, the wasp inadvertently pollinates the tiny blooms.
The hunter and the hunted
Females of this species close their nest entrance each time they leave. With no opening at the top of her dirt mound, predators and parasites are less likely to pay a visit. Each morning, after she seals the door, the female performs an orientation flight, circling close to the ground in larger and larger loops until she learns the lay of the land.
P. crabroniformis females hunt bees by going from flower to flower or by surveilling the entrance holes of ground-dwelling bees. They prefer Halictids (sweat bees), which are small and easy to subdue with a quick sting. Once the prey is paralyzed, the wasp carries it home tucked against her thorax and secured with her midlegs.
Hunting is an all-day affair because each brood cell requires 12 to 16 bees, depending on their size. If Halictids are in short supply, P. crabroniformis may occasionally opt for a small wasp or a somewhat larger bee. Although Philanthus species in general hunt a variety of bees, one European species, P. triangulum, limits itself to honey bees.
Random acts of pollination, whether on purpose or quite by accident, keep our flowering plants healthy and genetically diverse. For a thriving planet, we need to keep our pollinators healthy and diverse as well, even if they come in the unexpected form of a wasp.
Rusty
Honey Bee Suite
About Me
My love of bee science is backed by a bachelor’s degree in Agronomic Crops and a master’s in Environmental Studies. I have written extensively about bees, including a current column in American Bee Journal and past columns in Two Million Blossoms and Bee Craft. In recent years, I’ve taken multiple courses in melittology and made extensive identifications of North American bees for iNaturalist. My master beekeeping certificate issued from U Montana. More here.