Mann's mollusk-eating ground beetle (Scaphinotus mannii)

Physical description

The Mann’s Mollusk-eating Ground Beetle is a large, flightless ground dwelling beetle. Adult beetles are approximately 23 mm long. Adults have narrow, elongated heads and jaws, an adaptation for feeding on shell-bearing mollusks.

Ecology and life history

The Mann's mollusk-eating ground beetle is a habitat specialist that requires areas of seasonally moist soil associated for the most part with daylong shade. Beetles have commonly been found in rocky drainages, and may be found in at the margins of damp canyons that are not subject to periodic inundation of water from dams.

Both adults and larva are known to eat slugs and snails and their eggs. Development from egg, through three larval stages, to pupation and adult stage probably takes one year and only one generation of the beetle is produced per year. The adult life span is estimated to be about a year. Adults emerge from pupae in early spring, become inactive in summer, and are active again in the fall until temperatures become too cold. Adults are nocturnal, sheltering under rocks, logs, or other cover during the day. Adult beetles are flightless, so active dispersal is limited to walking, and no passive dispersal agents are known.

Geographic range

In Washington, the Mann’s mollusk-eating ground beetle is present at elevations up to 870 m in the Asotin Creek drainage, the Washington mainstem and tributaries of the Grande Ronde River, the west side of the Snake River, and the Tucannon River drainage (Asotin and Whitman counties).There is one record from northeast Oregon, and the species has recently been found in Idaho.

This beetle was originally found in damp canyons amid shaded forest or shrub patches associated with springs or small streams. However, further research shows that they are not limited to these conditions and are often found in areas a considerable distance away from creeks or riparian areas. The primary habitat requirement for this species is at least seasonally moist soil associated for the most part with daylong shade, the latter necessary for maximal soil moisture retention and heat buffering. Beetles have commonly been found in rocky drainages with rocks providing diurnal and seasonal shelter for the beetles, as well as their snail prey. The association with rocky habitat appears to be stronger than habitat with riparian vegetation.