Colletes halophilus, the sea aster mining bee, is a rare species of mining bee from the family Colletidae which is found around the margins of saltmarsh and other coastal habitats in south-eastern England and north-western Europe. It is threatened by rising sea levels and human development which reduce its food plant sea aster (Aster tripolium) and destroy its nesting areas. Description Colletes halophilus is a striking short-tongued mining bee which has its thorax coated with reddish brown hair, and a black abdomen with contrasting pale whitish to yellow bands. The females are larger and brighter than the males. C. halophilus adults have a length of 11–14 mm. There are two similar western European bee species—the ivy bee (Colletes hederae) and the common colletes (Colletes succintus)—but these are ecologically separated from C. halophilus. Distribution Colletes halophilus has a highly restricted distribution, being found in coastal eastern England from Spurn Point southward along the east coast past the Thames Estuary, and along the south coast as far as Hampshire and easternmost Dorset. Outside England, C. halophilus has a restricted distribution on the Atlantic coastal regions of western Europe, from the Frisian Islands in the north to the Bay of Biscay coasts of south western France. Habitat C. halophilus is strongly associated with saltmarshes. The nesting aggregations are situated at the inland edges of the saltmarshes out of the reach of all but the highest tides and close to sources of food. The sites chosen for nests are usually bare sandy soils, which are warmer than the surrounding vegetated areas due to exposure to the sun, often placed on south-facing slopes. As well as natural habitats, C. halophilus uses manmade habitats such as former industrial or brownfield sites, sea walls, and piles of sand. Biology Colletes halophilus are "solitary bees", but they nest in aggregations, which can sometimes number in the thousands. They nest in bare soil—for example, where vegetation has been removed by land slips—in soil heaps, and even in and around the burrows of European rabbits. The nesting sites are located at the edge of saltmarshes and may occasionally be flooded by the highest spring tides; bees have been observed emerging from recently submerged mud. Each female digs her own burrow, creates the cells, and provisions them on her own. Each nest consists of a short, curved burrow which terminates in a cluster of around half a dozen cells which radiate