Anthidellum sp. (Megachilidae)

Megachilids tend to be medium-sized bees with relatively stout bodies [1]. This large family, well represented in the Northwestern U.S. [2], can be distinguished from other bees by the location of their pollen-collecting scopae (i.e. pollen baskets), which are found on the ventral side of the metasoma of females and not on the hind legs.

These bees are all solitary and have diverse nesting behaviors, many megachilids prefer to nest in preexisting holes.

Leafcutter bees

Megachile rotundata

The “leafcutter species” (genus Megachile) get their name from their habitat of lining nest cells with small pieces of leaves cut from plants with their mandibles. Nests may be made in hollow stems, small cavities, beetle burrows, soil banks, walls, etc. Many leafcutter bees are about the size of honey bees [2]. The introduced and managed alfalfa leafcutter bee (species Megachile rotundata) is an important pollinator of alfalfa in western states [1].

Osmian close-up on lupine
Osmia (sp.) on lupine
Mason bees

The “mason bee” species (genus Osmia) of this family, which are often dark blue or green metallic in coloration, get their name from their habit of constructing nest cells with mud or chewed materials such as leaves [3]. This large genus is well represented in western North America. Key characters of this group include the ventrally located scopae, equal sized submarginal cells (2) of the wings and subantennal sutures that run from the outside edge of the antennal sockets to the clypeus [3].


1. Triplehorn and Johnson, 2005

2. Stephen et al., 1969

3. Michener, 2007