These members of the genus Renardia are among the more than 59,000 different species of rove beetles, or Staphylinidae, known from around the world.
Both the dark adults and their paler larvae (immatures, lower right photo) are very flat, as seen in the top photo. This is an evolutionary adaptation to where they live – under the tight bark of rotting logs.
Most rove beetles are predators that feed on small insects and other animals, but Renardia and its relatives eat decaying wood, including the microscopic fungi and bacteria that break the wood down. You can see such dark material inside the pale larva’s long looped gut that runs along its midline.
These are typical-sized rove beetles, about 3 mm (1/8 inch) long, but others range from under 1 mm (1/25 inch) to about 30 mm (1.2 inch) long.
Most Renardia species and their relatives live in tropical areas, but the adult shown here was found in the mountains in Utah in November, walking under the bark of a small log, with ice around it (and others) under the bark! These adults, like most rove beetles, can fly when needed, but usually have their flight wings folded up very small under their short elytra (wing covers), which are the evolutionarily modified front wings that are characteristic of beetles. The short elytra and exposed abdomen occur in nearly all rove beetles; their resulting flexible bodies seem to let them live in tiny tight places that most more-rigid adult beetles cannot move around in.
Thanks to this week’s special contributor, Margaret K. Thayer, Division of Insects, Zoology Department.
© The Field Museum, Photos taken by Gracen M. Brilmyer, under the direction of Margaret K. Thayer.
Learn more about rove beetles at http://archive.fieldmuseum.org/peet_staph/