California Beetle Project > Species Pages > Brachinus mexicanus/pallidus
Scientific name: Brachinus mexicanus/pallidus
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B. mexicanus B. pallidus
The two species B. mexicanus and B. pallidus are very difficult to distinguish by only looking at external characteristics, so they are described together here.
What they looks like: 7-9 mm in length. 3.0-4.6 mm in width. Wing-covers blue with highly defined ridges and with dense hair only between the outer few ridges and on the posterior end. Head, pronotum (dorsal part of the thorax), and abdominal segments brown to reddish brown.
Where you'll find them: Throughout the southwestern United States and Mexico, and sporadically in dry floodplains in the northwestern and midwestern United States.
Natural History: These are the most well known species of the genus Brachinus. They are parasites of hydrophilid water beetles and other streamside pupae. The first larval stage finds a pupa and eats its insides. Then it makes its home in the shell of the pupa and pupates there.
Many details of the life of these beetles regarding their lifestyles are unverified or unknown, but they are assumed to be a nocturnal generalist predators and scavengers. They are usually found in rocky, streamside areas. These places include weathering, layered sandstone and varied, jagged areas, such as on the undersides of rocks. Also found on slopes or moist areas where conditions are highly varied. With the ability to thrive in places other organisms have a hard time getting to, populations of these species tend to be denser than those of others.
This page was written by David Honsberger, a 2005 participant in the Quasars to Sea Stars teen program.