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_Philonthus varians_ and insect dissection

In order to arrive at species determinations for several species I collected in my Masters work, I needed to learn how to dissect insects, as the only way to figure out what some were was to look at the shape/features of the aedeagus (analogue of a penis), and in some cases, the ootheca. Primarily, it was small rove beetles (Coleptera: Staphylinidae) in the subfamily Aleochainae that required dissection to identify, but, I spent time practicing on various taxa to get things right. The specimen above, Philonthus varians (Paykull), was one done for practice, though the dissection certainly helped to solidify the species determination.

When dissecting genitals from staphylinids, the two terminal segments of the abdomen are removed, the tergite and sternite of the penultimate segment and the terminal segment get mounted on the left of the celluloid microslide, and the aedeagus on the right side, preserved/mounted in Canada balsam. The clear slide and mounting medium allow for easy inspection of the parts mounted to the slide under a scope from most angles.
The rest of the specimen may be pinned/pointed, if ventral features are important diagnostics, or carded, as this one is, and both the specimen and slide are pinned together on the same pin, along with their locality/collection label, Unique ID number label (for specimen tracking in a collection/database) and species determination label.

Class: Insecta
- Order: Coleoptera
— Superfamily: Staphylinoidea
—- Family: Staphylinidae
—— Subfamily: Staphylininae
——- Tribe: Staphylini
——— Subtribe: Philonthina
———- Genus: Philonthus

Philonthus varians is a small beetle, ~6-8 mm long, associated with decaying litter and dung. Given that my work had me collecting on a pasture, full of dung, and certain treatments with relatively substantial litter, it’s little surprise that it was collected. It’s something of an open habitat generalist, being found in meadows, pastures and other agricultural land, and even intertidal and saline habitats. It is a palearctic species, with adventive populations in North America.

Rove beetles are primarily predators, though the family includes some fungivores and necrophages. Philontus varians is pretty typical in that it is a predator of other soft-bodied insects (primarily dipteran larvae) living in, on, or under the pasture litter and manure; it also appears to be primarily a diurnal hunter.

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