Why these coastal bees spend their spring building elaborate sandcastles by the sea

Nature · Published 29 September 2026 · Updated 24 October 2026 Swipe more like this →

In short: While beachgoers relax on the sand, the bumblebee-mimic digger bee is busy at work. These industrious insects construct specialized nests within sandy cliffs overlooking the Pacific Ocean. By transporting water to soften the earth, they create secure environments for their offspring, showcasing a remarkable adaptation to a challenging coastal habitat.

The bumblebee-mimic digger bee, known scientifically as Anthophora bomboides stanfordiana, inhabits coastal regions in Northern California and Oregon. During the spring, after mating, the female bees focus their energy on excavating nests. Unlike bees that occupy pre-existing cavities or wood, these diggers carve their homes directly into the sandy cliffs that overlook the Pacific Ocean.

To facilitate this excavation, the bees employ a sophisticated method. They locate nearby water sources, such as streams, and ingest water into a specialized abdominal pouch called a crop. A single bee may undertake as many as 80 trips daily, spraying the collected water onto the cliff face to soften the sand. This process allows them to dig a series of holes where they lay their eggs, effectively building a functional sandcastle for their developing young.

This behavior is part of a broader trend in the insect world, as approximately 70% of global bee species nest underground. When these bees build their burrows in close proximity to one another, the phenomenon is referred to as gregarious nesting or an aggregation. Beyond their architectural skills, these bees utilize mimicry as a survival strategy. Although they are harmless and do not sting, they bear a striking resemblance to the yellow-faced bumblebee, Bombus vosnesenskii, which does possess a stinger. This visual deception serves as a deterrent against potential predators.

The diversity of nesting habits among bees is vast. While the digger bee favors sandy cliffs, other species have evolved different strategies. Mason bees, such as the blue orchard bee, prefer narrow cavities like hollow twigs, while carpenter bees are known to excavate their nests within wood. Understanding these varied nesting behaviors provides insight into how different species have adapted to their specific environments, ensuring the survival of their offspring across diverse landscapes.

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