Megalodacne fasciata, above
Megalodacne heros, below
Length: 9 - 15 for Megalodacne fasciata
Length: 18 - 21 for Megalodacne heros
These are two attractive species in the family Erotylidae, the Pleasing Fungus Beetles. These are the only two Nearctic species in the genus Megalodacne.
Differences between the two species? Megalodacne fasciata is the smaller of the two (see length ranges for both species above). As for elytral markings, the area to examine is the black rectangle that lies on the elytra where they meet the pronotum. On Megalodacne heros the orange color curves around, forming two sort of "C" shapes at the left and right of the black rectangle, with the orange color partly surrounding the black rectangle at left and right on the front of the beetle. On Megalodacne fasciata the orange does not curve around the black rectangle, or does so only slightly. Also, on Megalodacne fasciata there is a round black spot on each each elytra near where it meets the pronotum. On Megalodacne heros this dot is present on each elytra but is often not so round in shape. The illustration below shows these differences in elytral markings.
One final difference is that M. fasciata has rows of fine punctures on the elytra while M. heros does not.
Where the elytra meet the pronotum:
Below left is Megalodacne fasciata
Below right is Megalodacne heros
Above: a group of Megalodacne heros feeds on fungus on the side of a fallen log.
Records (in blue-green) of Megalodacne fasciata, above; M. heros, below