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Desmocerus californicus dimorphus, Valley Elderberry Longhorn Beetle

Valley Elderberry Longhorn Beetle

One of California's two officially threatened beetle species, Desmocerus californicus dimorphus derives its name from its endemism to California and the striking sexual dimorphism displayed by the adult beetles. The bright colors and relatively small size of the VELB make it a model "charismatic microfauna" species, attractive to the public and thereby more conducive to widespread sympathy and conservation proposals.

VELB is completely dependent on native elderberry trees (Sambucus spp.); it is highly susceptible to habitat degradation and has already been isolated into "metapopulations" based on distribution of Sambucus. The critical habitat in which native elderberry occurs often coincides with or borders on the broader riparian ecotopes, including freshwater wetlands and vernal pools. The latter are host to California's other threatened beetle, the Delta Green Ground Beetle (Elaphrus viridens) and its host, Soleno grass. ( Conservation plans for riparian areas are therefore doubly beneficial: both insects can benefit from a common protected habitat.

While human disturbance and habitat fragmentation are undoubtedly the primary threats to VELB populations, other insects may also pose a threat. An invasive Argentine ant has recently been shown to affect the beetles' distribution: in VELB habitat where ants are found, the beetles almost never occur (Huxel, G.R., 2000.) Additional troubles for VELB might arise from pesticides or biocontrol meant for invading "pest" cerambycids such as the brown spruce longhorn beetle, Tetropium fuscum, and the Asian longhorn beetle, Anoplophora glabripennis. These two rogue longhorns can girdle, weaken, and destroy native trees at an alarming rate, but have not yet spread west of Illinois. Control of pest longhorns should not pose a serious threat to VELB unless broad chemical controls are used: the three species have no host tree in common.

Despite its inherent charm the VELB has been the focus of some small controversy: in 1997, a self-proclaimed conservation organization known as the "National Wilderness Institute" petitioned the Secretary of the Interior to delist a number of endangered and threatened species, including the VELB and the host plant of the Delta Green Ground Beetle. Objections included newly-discovered species abundance and objection to subspecies as "real species." Rob Gordon, the NWI director, offered the following argument:

"If imaginary species are suitable candidates for the endangered species program then the Secretary ought to add bigfoot and the Loch Ness monster - if not, then species which were added to the list by mistake should be removed." While Desmocerus could act as an umbrella species for the protection of dwindling riparian and wetland habitats, legal and scientific honest mandates further investigation into the subspecies taxanomic validity.


Collinge, Sharon, Marcel Holyoak, Cheryl Barr, Jaymee Marty. Riparian habitat fragmentation and population persistence of the threatened valley elderberry longhorn beetle in central CAlifornia. Biological Conservation. 2001. 100 (1): 103-113

Written by: Ainsley Seago 2002

Updated 2008

Image credit: Richard Arnold, Entomological Consulting Services, Ltd.