Genus: Trachusa Panzer, 1804
Subgenera: Archianthidium, Congotrachusa, Heteranthidium, Legnanthidium, Massanthidium, Metatrachusa, Orthanthidium, Paraanthidium, Trachusa, Trachusomimus, Ulanthidium
Common name: “handsome bee” (Trachusa larreae)
Trachusa means “roughened,” which they were likely named after due to the coarse punctations covering their thorax (Wilson and Carril 2016). Trachusa are medium to large bees, ranging in body length from 8.5–20 mm, that are sometimes hairy (Michener 2007). Trachusa is thought to have the most primitive characteristics of all Anthidiini (Michener 1941). Unlike most other anthidiines, Trachusa spp., aside from those in the subgenus Heteranthidium, lack yellow or white maculations on their body (Michener 2007).
Trachusa contains 52 species in 11 subgenera worldwide (Michener 2007). There are 19 species known from North America.
(modified from Michener 2007 unless otherwise stated)
Most Trachusa can be distinguished from other anthidiines by their lack of maculations (except for in subgenus Heteranthidium) (Michener 1941; Michener 1948). The lack of carinae and the blunt projection on the front tibia can help separate Trachusa from other robust anthidiines (Michener 2007).
There are no known invasives.
Trachusa have been observed visiting a wide variety of different flowers, including Triteleia ixiodes, Rhamnus crocea (nest material), Larrea spp., as well as plants in the families Lamiaceae, Leguminosae, Asteraceae, and Dipsacaceae. T. larreae, however, is specialized on Larrea tridentata (Cane 1996).
Trachusa are solitary bees which dig their own nests in the ground (Michener 2007). Trachusa perdita nests consist of a single, broadly curved tunnel dug into loose, sandy soil (Michener 1941). The nest cells that have been studied are made up of irregularly cut pieces of Rhamnus crocae and are cemented to the sides of the tunnel with a resinous gum (Cane 1996). In contrast, T. bysinna have been observed nesting in groups of as many as fifty females, with nests that sometimes have branching tunnels rather than the single curved tunnels of T. perdita. The nesting biology of T. (Heteranthidium) larreae has been well described (MacSwain 1946; Cane 1996; Rozen and Hall 2012). Trachusa larreae surrounds the entrance of its nest with pebbles and twigs. The nest tunnels are about 7 mm in diameter and 8–19 cm long (MacSwain 1946; Cane 1996). The nest tunnels are unbranched and descend at a 25°–30° angle with the soil for several cm before turning abruptly at a 45° angle and opening to an entrance chamber from which the nest cells radiate. The walls of the cells are made up of a greyish-green resin mixed with soil (Cane 1996). Isolated nests of T. larreae have been found, as well as huge perennial nesting aggregations spanning as much as 95 m long (Cane 1996).