This Fly Torpedoes a Bindweed Bee’s Nest | Deep Look 

A “bee fly” looks a bit like a bee, but it’s a freeloader that takes advantage of a bindweed turret bee’s hard work. The bees dig underground nests and fill them with pollen they collect in the form of stylish “pollen pants.” As the bees are toiling on their nests, the flies drop their own eggs into them. But the bees employ a tricky defense against the flies.
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In the spring in California, male bindweed turret bees get into brawls with their peers as they search for a female to mate with. Males pile onto each other and form so-called “mating balls,” an inaccurate name, since no mating is occurring. Rather, the males are getting into fights. The female they’re vying for is caught at the bottom, and sometimes the battle is so intense the males accidentally kill her. But, if she survives, she and the male who won steal away and mate.
Once they’ve mated, females dig through compacted dirt to make a nest underground, where they’ll lay their eggs. The majority of the world’s bee species - 70 percent - are ground-nesting. The bindweed turret bees in this video chose a dirt parking lot near the town of Winters, in the Central Valley. These native bees are known by the scientific name Diadasia bituberculata.
Females tirelessly scoop earth with their mandibles, softening it by dousing it with nectar they collected earlier. They work side by side, but each is “queen” of her own castle.
As they dig out their nest, they often build a turret at the entrance. These dirt towers usually aren’t vertical: Many of them are tunnel-like, with a sideways entrance. Others curve down. With their entrances facing away from the sky, the turrets protect the bees’ nests when bee flies start dropping their eggs from the air.
--- What is another name for a bee fly?
Bee fly is the common name for the more than 4,000 species of flies in the family Bombyliidae.
--- How do bee flies parasitize bees?
The Paravilla fulvicoma bee flies in our video drop their eggs into the nests of bindweed turret bees. When the fly’s egg hatches into a larva, it digs tiny hooks into a bee larva. But the bee larva doesn’t die. It grows by feeding on the pollen that its mother packed for it inside the nest. As the bee larva grows, the fly larva sucks it dry and kills it. Then the fly finishes growing into an adult and pushes up through the ground to emerge the following spring.
--- How do you tell a bee fly from a bee?
Even though bee flies have hairy bodies like bees, if you look closely, you can tell them apart. Bee flies have big eyes that cover a large area of their heads. And bee flies’ antennae are short compared to bees’ antennae.
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