Proteininae can be recognized by the following combination of characters (Fig. 1.16.1): size small (1-3mm long), body oval with elytra at least twice as long as the pronotum and covering at least one tergite, pronotum strongly transverse (at least twice as wide as long at the base), and antennomeres 1 and 2 much wider than 3 and 4. Proteinines somewhat resemble some omaliines but always lack ocelli (proteinines do not resemble those few Omaliinae that sometimes lack ocelli).

Two genera are widely distributed in North America: Proteinus Latreille and Megarthrus Stephens. The former has the hind angles of the pronotum rounded and in the latter they are pointed (Fig. 9.14.1). Both genera can be found on decaying fungi and in leaf litter; however Megarthrus can also be collected from carrion and dung (Cuccodoro and Löbl 1996). Megarthrus is has been collected successfully with window, flight intercept, and pan traps, especially when baited with fungi, carrion, or dung. Several species of Proteinus were captured in pitfall traps in New Brunswick red spruce forests; two of these were recently described as new (P. pseudothomasi Klimaszewski and P. acadiensis Klimaszewski) (Klimaszewski et al. 2005). The proteinine species of ECAS are probably mainly mycophagous and/or saprophagous (Thayer 2005) but some species are at least partly predaceous on nematodes (Cuccodoro 1995).