not quite a tiger beetle…
though often mistaken for one, Elaphrus ruscarius a member of a genus of intricately sculptured, strikingly colored beetles. Their resemblance to tiger beetles is so strong that the first described species had been placed in the genus Cicindela. However, in addition to being a good deal smaller, they lack the maculations and vivid coloration common to most tiger beetles.
The most widespread species of Elaphrus in North America, E. ruscarius ranges from southern Maine and northern Minnesota as far south as northern Florida and eastern Texas. As with other members of this genus, E. ruscarius is found on the banks of streams, rivers, and other bodies of water – usually on substrate that is moist to the touch. They behave much like tiger beetles, darting around in search of prey, in and out of the cover of surrounding vegetation or cracks in the substrate.
The elytra are covered with small sculptured pits – often strongly contrasting with the surrounding area of each elytron. The size of the pits is correlated to the roughness of substrate which that species occurs on; the courser the substrate, the more indented the pits (1). Another intriguing feature are elytral mirrors – visible in the photo below – dark reflective patches that mimic the light reflected by water between particles of the substrate.
Members of this genus vary in coloration from smooth, oily blacks with deep blue pits on the elytra, to the typical olive gray/greens, such as E. ruscarius, to the bright green E. viridis – a federally threatened species found only in California. Some species also have alternate color forms; E. ruscarius has a less common red/copper form – pictured here – it is found primarily on red-colored substrate.
For more information on Elaphrus, check out the Bugguide page here.