The members of the subfamily Omaliinae are often active during the cooler times of the year. Some larvae that I had recently collected have finally pupated. This individual has started to get some pigment so I decided to take the opportunity and photograph the guy – otherwise the pupae are so lightly colored it gets difficult to distinguish them from the background.
Omaliinae pupa, ~24 hrs. prior to eclosion
Omaliinae have a diagnostic ventral abdominal defensive gland on segment VIII. In this pupa, this defensive gland appears as a darkened band near the posterior end in the ventral shot.
Often, female insects store sperm in a tube-like structure known as the spermatheca. In most staphylinids, spermathecae are sclerotized and in several groups the structures are unique at the species level. Interspecific differences are particularly prevalent in aleocharines and spermathecal morphology can be extremely elaborate.
This is a spermatheca which starts (it ends in the large bulb) out as a tight coil, only to back-track as large loops that circumvent the original tight coil – strange. This morpho-type has evolved independently in several aleocharine lineages. In some cases, the length of the male copulatory structures correlate to female spermathecal length, possibly due to some sort of “lock and key” relationship, but this is not the case in this species. Another possible explanation for this morphology, is that the sperm themselves have extremely long flagella, and the coils are merely to keep the structure compact. This would be an interesting avenue of inquiry.
All representatives of the aleocharine subtribe Gyrophaenina feed on spore of macro-fungi, the mushrooms that we’re mostly familiar with. And in order, I guess, to neatly fit in between the gills of a mushroom (where the spores are produced), most gyrophaenines have flattened bodies.
Some genera, to the contrary, are collected by sifting various debris where the beetles are thought, by me, to feed on mold spores. This is because those mouthpart characters that have been attributed to be adaptive to gathering spores in mushroom gyrophaenines are also present in litter-inhabiting gyrophaenines.
Meet Encephalus americanus, the only species of the genus in North America.
Only three other species are described in the genus, E. complicans in Europe, E. laetulus and E. zealandicus from New Zealand. It appears that E. complicans and E. americanus are associated with bog-margin litter, which is correlated with their northern distributions. Interestingly, these litter-inhabiting gyrophaenines are not flattened but compact and stumpy looking. Maybe when they are threatened they curl up and fall through the matrix of litter-substrate?