Where do pollinators nest?

Our native bees generally nest in the ground; a few chew out the pith of berry canes, or take advantage of tunnels in wood left by beetle larvae. “Miner” and “digger” bees tunnel in sandy soils; “carpenter” bees tunnel into dead canes; “leaf-cutter” bees glue bits of leaves together with saliva; “mason” bees daub the walls of nests with clay-rich mud; and “cellophane” bees line nest cells with a polyester secretion that dries into a translucent membrane. Most native bees are solitary: every female builds her own nest with one cell for each egg and its pollen-rich food supply. Some bees build community nests for shared defense against nest predators and parasites, however, in which a number of tunnels branch off a single entrance. Bumblebees are unusual in forming queen-centered families of related female workers that build rambling nests of round wax chambers with eggs protected and fed by all of the sisters.

Bees must return several times each day to their nests with pollen loads. Bumblebees can lift about half their weight in nectar and pollen and fly several kilometers between foraging areas and their nests, even between islands. Like domestic honeybees and social wasps,

bumblebees must feed several generations each summer, and they work collectively over a much larger geographical area than solitary bees. Small solitary bees carry small payloads and may make more trips each day than bumblebees, although over shorter distances. Most solitary bees nest within a few hundred meters of floral resources.

Halictus ligatus, American Camp, San Juan Island

Some bees and hover-flies have abandoned the hard work of collecting pollen: they simply lay their eggs in others’ nests. Cuckoo or kleptoparasites mimic their hosts’ appearance, helping them avoid attack while they loiter near nests. In some studies of bee hotels, cuckoos hatched out of nearly one-third of the nests!

Hover-flies do not have nests; they lay their eggs close to appropriate food resources, which for the Syrphini are flowering plants covered in aphids. The eggs hatch into larval flies resembling tiny flattened caterpillars that feast on the aphids. After two weeks of voracious eating the larvae pupate into adults and go in search of more aphid infestations. Most other hover-flies (the Eristalini) lay their eggs in warm shallow water. Their tadpole-like larvae feed on detritus, algae, and smaller animals such as insect larvae until they are ready to pupate into nectar- and pollen-eating adult flies.

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