Numbers
Genus has forty to fifty North American species--see print references cited below.
Identification
Medium-sized beetles with dark (blue, green, or blackish) elytra that contrast strongly with orange head and pronotum. Elytra are wider than pronotum. Some species flightless
(1).
Mimicked by other ground beetles such as Galerita, and by some longhorned beetles.
Habitat
Found under loose bark, rocks, boards, etc. Also found on ground in open at night. Usually associated with floodplains, edges of temporary ponds.
Season
Typically spring, early summer and fall? March-July, September-October (B. alternans, South Carolina).
Life Cycle
Eggs laid singly in mud cells made on plants, rocks. Larvae are external parasites of dytiscid beetles such as Hydrophilus. Larvae also scavenge body of host after its death. A few species parasitize whirligig beetles, Gyrinidae. Larvae have reduced legs, typical of parasitic forms. Pupation occurs inside the body of the host. Adults have impressive chemical defenses, ejecting toxic, foul-smelling gases from their abdomen with a loud popping sound. The explosive brew is composed of hydrogen peroxide, hydroquinone, and catalytic enzymes.
Print References
Ciegler, pp. 33-36, describes, keys to the 16 South Carolina species
(1).
Sikes, pp. 76-77, lists 12 species for Rhode Island
(2)
Dillon, pp. 107-108, plate XI, describes and illustrates two species
(3).
Papp, p. 51, fig. 141--B. americanus
(4)
Arnett and Jacques, p. 98, fig. 254
(5)
White, p. 94, fig. 31
(6)
Milne, p. 537, fig. 166
(7)Internet References
National Center for Science Education--discussion of mechanism of chemical defenses
Clemson University--discussion of chemical defenses under account for
Galerita 
