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San Joaquin dune beetle
Coelus gracilis

Drawing by Kris Buenger


U.S.A. candidate for listing

Life History

Little information exists on the feeding habits of San Joaquin dune beetles, though they are probably detritivores, feeding on decomposing vegetation buried in the sand. Some other related beetles feed mostly on dung. Nothing is known about the mating system or breeding season of San Joaquin dune beetles. In general, female beetles lay eggs singly or in masses, with hatching occurring after several days. The presence of immature dune beetles and larvae is evident throughout the year, which suggests that oviposition (egg laying) occurs over a long period of time. The larvae develop and pupate exclusively in the sand. Pupae have been found in the wild only in late spring and early summer. In the laboratory, adult dune beetles are capable of living at least 6 months, and in the wild they may live for a year or longer.

The hot summer climate of the San Joaquin Valley prevents a majority of beetles from emerging from the sand, so active periods range from about November through April. Activity also coincides with the growth period of the winter ephemeral plants under which San Joaquin dune beetles reside. Adult dune beetles spend a majority of their time in sandy soils, whereas larval forms are found exclusively in loose sands. Adults typically are found 5 to 10 centimeters (2.0 - 3.9 inches) underground under a canopy of vegetation, and less often under ground with a bare surface.


Historically, the range of the San Joaquin dune beetle extended from Antioch, Contra Costa County, in the north to the Kettleman Hills, Kings County in the south. They inhabited inland sand dunes within this range. Currently, this beetle is restricted to small isolated sand dunes (250 - 10,000 m2) along the western edge of the San Joaquin Valley. The population located near Antioch, Contra Costa County, apparently has been extirpated.

Although no direct evidence exists of a population decline of San Joaquin dune beetles, it is inferred from the widespread loss of sand dune communities in the Valley and apparent disappearance from near Antioch, Contra Costa County, California. A recent threat was ORV (off-road vehicle) use on dune habitats near Kettleman City and Monocline Ridge, Fresno County, but ORV use apparently is now controlled or eliminated in those areas.


Order COLEOPTERA, Family TENEBRIONIDAE, Subfamily TENTYRIINAE, Genus Coelus, Species gracilis



Recent Synonyms


Other Common Names



Doyen, J.T. 1976. Biology and systematics of the genus Coelus (Coleoptera: Tentyriidae). J. Kansas Entomol. Soc. 49:595-624; Gordon, R.D., and O.L. Cartwright. 1977. Four new species of Aegialia (s. str.) (Coleoptera: Scarabaeidae) from California and Nevada sand dunes. J. Washington Acad. Sci. 67:42-48; U.S. Fish and Wildlife Service. 1978. Endangered and threatened wildlife and plants; proposed endangered species or threatened species status and critical habitat for 10 beetles. Fed. Register. 43:35637-35643.; White, R.E. 1983. A field guide to the beetles of North America. Houghton Miffline Co., Boston, MA. 368 pp.


No information given.


The San Joaquin dune beetle, considered the smallest species of dune beetle, is found only in sand dunes in California. The body is fairly robust, dorsally inflated, and ranges in color from pale yellowish-brown to dark brownish-black. The female is slightly larger (15%) than the male.

Authors of Profile

T.M. Sandoval, C.D. Johnson, and D.F. Williams

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