To protect their young from parasitic flies, these bees build clever architectural defenses.
In short: The bindweed turret bee spends her life building elaborate underground nests, only to face aerial attacks from parasitic bee flies. To survive, these bees have evolved a brilliant structural countermeasure: building curved or sideways-facing turrets that shield their nest entrances from the flies' mid-air egg-dropping strategy.
The bindweed turret bee, known scientifically as Diadasia bituberculata, is a ground-nesting specialist native to California. During the spring, females laboriously excavate underground nests, softening the compacted earth with nectar. They provision these cells with pollen—often carried in visible 'pollen pants'—to nourish their future offspring. While they may work in close proximity to one another, each female operates as the independent 'queen' of her own subterranean castle.
These nests are frequently targeted by the bee fly, Paravilla fulvicoma, a member of the Bombyliidae family, which comprises over 4,000 species. The fly acts as a freeloader, hovering over the nest entrance to drop its eggs into the burrow. Once hatched, the fly larva uses tiny hooks to attach itself to a bee larva. It then consumes the bee larva while the latter feeds on the stored pollen, eventually killing it before emerging as an adult the following spring.
To counter this, the bees construct protective turrets at their nest entrances. Rather than simple vertical chimneys, many of these structures are curved or feature sideways-facing tunnels. By orienting the entrance away from the sky, the bees effectively block the flies' ability to drop eggs directly into the nest. This architectural adaptation is a critical defense for a species where 70 percent of the world's bee population relies on ground-nesting, leaving them vulnerable to such specialized parasites.
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Sources
- Summary by Intellect · source: This Fly Torpedoes a Bindweed Bee’s Nest | Deep Look
- Also: UC Davis Scientists Collaborate With 'Deep Look' on Bindweed Turret Bees | Entomology & Nematology News
- Also: www.pbs.org — Deep Look | This Fly Torpedoes a Bindweed Bee's Nest | Season 10 | Episode 10
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