Delta Green Ground Beetle
Delta Green Ground Beetle
|Listed||August 8, 1980|
|Family||Carabidae (Ground beetle)|
|Description||Dull golden above, metallic green beneath.|
|Habitat||Bare, sparsely vegetated ground along the edges of vernal pools.|
|Reproduction||One generation per year.|
|Threats||Loss of seasonal wetlands.|
The delta green ground beetle, Elaphrus viridis, is about 0.25 in (6 mm) long when mature. It is golden or bronze above and metallic green beneath. This beetle resembles a tiger beetle with its relatively large abdomen, smaller but distinct thorax and head, and long slender legs. It is smaller than the tiger beetle and has spotlike depressions on its leathery outer wings. Its antennae are short and blunt.
In general, the genus Elaphrus is associated with temperate wetland habitats. Many specific details of the life history of the delta green ground beetle are unknown. The primary food source is thought to be springtails (flealike insects of the order Collembola). The delta green ground beetle is active during the warmest and sunniest part of the day from early February to mid-May. The nocturnal larvae are found in greater concentrations and inhabit damper areas than adults. This species produces one generation per year. Both male and female may mate several times in their lifetimes. Females deposit eggs during winter and early spring after a delayed period of development during which the adults are inactive and metabolism is reduced.
Adult beetles inhabit the grassy edges of vernal pools that are filled by winter rains but dry up by late summer. Typically, the pools are small depressions within generally level terrain. Water inundates the area long enough to inhibit development of typical grassland vegetation. The climate is Mediterranean, with cool rainy winters and warm, dry summers. The beetle requires sparsely vegetated ground to utilize its concealing markings and keen vision.
Although this beetle was first described in 1878, its range remained a mystery until 1974 when a student from the University of California discovered a population at the Jepson Prairie in Solano County. The species was originally widespread in the once numerous vernal pools of central California.
The delta green ground beetle is known to inhabit two sites in Solano County, California, south of Dixon at Olcott Lake. A portion of the habitat falls within the Jepson Prairie Preserve, which is owned and managed jointly by the Nature Conservancy and the University of California, Davis. Between 1974 and 1985, only 75 individuals were observed at the preserve.
Many vernal pools have disappeared from the California landscape because of the increased human control of natural water flows. Rivers have been dammed and channeled for irrigation, and wetlands have been drained or filled for cropland. Only a few seasonal pools remain intact. Plowing and water pumping have already caused remaining pools to shrink or dry up earlier in the summer, a change in timing that has a critical impact on the life cycle of dependent insects. In 1980 plowing and grading damaged one inhabited pool, and further disturbance would probably eliminate the beetle from this site.
Conservation and Recovery
The Jepson Prairie Preserve already provides some protection for the delta green ground beetle, and critical habitat was designated to include both known population sites. Recovery will focus on limiting further habitat disturbance and translocating the beetle to other suitable sites within its range. A portion of Olcott Lake outside the preserve has been identified as a potential reintroduction site.
The recovery plan also calls for investigating the mortality factors, biological requirements, and population dynamics associated with the species; and the effects of grazing and prescribed burning on the habitat.
U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
Holland, R. F., and F. T. Griggs. 1976. "A Unique Habitat: California's Vernal Pools." Fremontia 4:3-6.
U. S. Fish and Wildlife Service. 1985. "Delta Green Ground Beetle and Solano Grass Recovery Plan." U. S. Fish and Wildlife Service, Portland, Oregon.