Mining Bees (lat. Andrena)

Life history

All Andrena are ground nesting, solitary bees. They seem to have a preference for sandy soils. The genus includes no parasitic or social species, though some nest communally or in aggregations. After mating, each female bee digs a burrow, excavating a series of small chambers called “cells”, lined with a shiny secretion, which she provisions one at a time with nectar and pollen to form firm, round pollen masses for the larvae to eat. Soil from the excavation process forms a small tumulus around the nest entrance. Larvae do not spin a cocoon and they overwinter as adults. They typically have one generation per year and adults are only active for a few weeks. Andrena nests are attacked by many other insects including brood parasitic bees, blister beetles, various parasitic flies, and Strepsiptera. Many Andrena are host-plant specialists, in which a species visits flowers of only a single or a few closely related plants. Oligolectic Andrena have specialized on many different plant groups and have morphological and behavioral adaptations that suit them for their pollen preference. For example, all members of the subgenus Callandrena specialize on pollen from the plant family Asteraceae and have highly branched, fluffy scopal hairs to hold aster pollen. According to Larkin et al. 2008, oligolecty was the basal trait for Andrena and a generalist diet has evolved multiple times across the genus.