Ground bees, including species like Mining Bees (Andrena), Digger Bees, and Sweat Bees, are solitary insects that create individual nests in the soil. These bees are non-aggressive, with each female constructing a burrow containing chambers, or brood cells, provisioned with pollen and nectar for her offspring. This concentrated, protein-rich food source and the developing larvae are highly attractive targets for a variety of animals. Predators have evolved specific methods to exploit the vulnerability of these nests, targeting either the subterranean brood or the adult bees flying above.
Mammalian Predators That Excavate Nests
Mammals with strong claws and a keen sense of smell are the primary predators that target the underground nursery of ground bees. Animals like skunks, raccoons, and badgers actively raid the nests to access the nutritious larvae and the stored pollen-nectar mixture. Skunks are notorious for the distinct, shallow, cone-shaped holes they leave behind when digging for the brood. These nocturnal hunters are drawn to the strong, concentrated scent of the brood provisions, which is a significant energy source. Badgers use their powerful forelimbs and long claws to quickly dismantle the underground structure, treating the entire nest contents as a single, protein-rich meal.
Avian Predators That Hunt Adults
Birds employ a different strategy, focusing on capturing the adult ground bees while they are active outside the nest during daylight hours. Species such as flycatchers and mockingbirds often perch near nesting areas, darting out to snatch the bees in mid-air or as they enter or exit their burrows. This aerial predation targets the female bees when they are most vulnerable, carrying pollen back to provision their nests. Woodpeckers, particularly the Northern Flicker, also act as ground bee predators, using their beaks to probe into the ground for shallow nests or adults near the surface. Other birds, like the Summer Tanager, catch the bee and rub it against a branch before consumption to remove the stinger.
Specialized Insects and Parasites
The most numerous and specialized threats to ground bees come from other insects and parasites that exploit the nest chambers themselves. Specialized flies, such as Robber Flies, are ferocious ambush predators that inject a paralyzing venom and liquefy the bee’s internal tissues. The larvae of Blister Beetles exhibit a unique parasitic behavior; they hitch a ride on a bee back to the nest, then consume the bee’s egg and the pollen provision.
Cleptoparasites
Cleptoparasitic bees, commonly known as cuckoo bees (Nomadinae), are silent invaders that do not build their own nests. The female cuckoo bee sneaks into the host’s nest chamber, lays her egg on the pollen ball, and the resulting larva consumes the food intended for the host. Parasitic wasps, sometimes called Velvet Ants, are ground-dwelling wasps whose wingless females seek out developing ground bee larvae to lay their own eggs on, turning the bee larva into a food source.