Brachinus Weber, 1801

Erwin, Terry L., 1965, A Revision Of Brachinus Of North America: Part I. The California Species (Coleoptera: Carabidae), The Coleopterists Bulletin 19 (1), pp. 1-19 : 3-4

Brachinus Weber

Brachinus Weber, 1801:22 .

( Carabus Linne, Fabricius ; Brachynus auct.)

TYPE OF GENUS: Carabus crepitans Linne , here designated. This was the second species listed by Weber, because bimaculatus (which Weber listed first) is now included in Pheropsophus Solier 1833 .

Description: Small to medium sized beetles with blue or brown elytra and ferrugineus head and thorax. The following characters are representative of this genus: second antennal segment short and all segments with at least some pubescence; eyes prominent and with a "bead"2 at dorsal edge; labrum short and broad; mandibles each with a single tooth; galae palpiform and two-segmented, with apical segment obconical; maxillary palpi four-segmented, with second and third segments obconical; labial palpi three-segmented, with first and second segments obconical; anterior tibiae with an "antennal comb" (formed of a fringe of stiff setae) in middle of posterior edge, and with an apical tibial spine; elytra costate to a variable degree, and truncate to dehiscent at apex; epipleura elevated above margin of elytra from humeri to outer apical corner; venter of thorax and abdomen mostly pubescent; middle coxal cavities disjunct; abdomen with seven visible sterna; parameres of male genitalia glabrous, reduced, the right one being very much smaller than the left.

These beetles, when alarmed, forcibly eject a liquid (composed in part of nitrogen and P-benzoquinone) from the pygidial glands that are located in the caudal half of the abdomen under the reproductive organs. This liquid volatizes instantly upon contact with the air, generating a small puff of "smoke" accompanied by an audible popping or crackling sound. If this liquid touches human skin, the skin will burn for an instant and then turn dark brown which lasts for several days, eventually fading to normal color.

Enemies of Brachinus (birds, insects, skunks, etc.) no doubt will be affected in much the same manner and will not "forget" the lesson. The popping will act to scare any enemy capable of hearing, and the puff of "smoke" would serve to startle an enemy. This ability to crepitate has resulted in both the common name of these beetles ("bombardier beetles") and in many of the species names such as Brachinus explodens Duft. , B. crepitans (Linne) , B. fumans (Fab.) , and B. librator Dejean.

Brachinus beetles are usually not far from water, in streamside, lakeside, or marshy habitats. Most members of this genus are capable of flying and do so when the food supply is scarce or the environmental conditions become unsuitable.

KEY TO BRACHINUS OF CALIFORNIA3

1. Mentum flat or slightly convex, with scattered setae; elytra with at least the 8th interval4 densely pubescent2----------------------------____________ 2

Mentum concave, surrounded by a ring of setae; elytra without dense pubescence in any interval-------------------------------------- COSTIPENNIS Motschulsky

2. Elytra with dense pubescence restricted to 8th interval, but scattered hairs may occur on the apical third of elytra------------------------ GEBHARDIS new species

Elytral pubescence not restricted to 8th interval--------------------------- 3

3. Elytra with pubescence restricted to 6th, 7th, and 8th intervals at middle (but also covering most of the apical third of the elytra)------------------------ 4

Elytra with entire dorsal surface pubescent -------------------------------- 6

4. Elytra blue, with blue epipleurae--------------------------------------- 5

Elytra brown, with testaceous epipleurae------------------------ LATERALIS Dejean

5. Antennal segments 3-5 usually black, at least in part (rarely ferrugineus), outer segments dusky; mesepisterna and sides of abdomen black; last 3 abdominal terga darkened, usually black ---------------- - --------------------- FIDELIS LeConte

Antennae pale ferrugineus; abdomen, mesepisterna and last 3 terga pale ferrugineus (browner in some populations) ------------------------------ PALLIDUS new species

6. Pronotum smooth or shallowly rugose -------------------------- - ----- 7

Pronotum with deep punctations forming a strongly rugose surface- FAVICOLLIS new species

7. Pronotum strongly cordiform, with sides more or less explanate before the middle; abdomen and mesepisterna black; antennal segments 3-11 entirely black ------------------------------------------------- TSCHERNIKHI Mannerheim

Pronotum narrow, distinctly longer than wide and with sides not explanate; venter

pale; antennal segments 3-11 dusky------------------------------------ 8

8. Elytra feebly costate, feebly pubescent; pronotal disc glabrous, with only a few scattered hairs around margins; head with frontal furrows deep and rugose ----------------------------------------------- IMPERIALENSIS new species

Elytra not costate, densely pubescent; pronotal disc with dense pubescence; head with shallow frontal furrows --------------------------- VELUTINUS new species