[1][2] T. tenebricosa measures 15–20 mm in length, is blue-black in colour and is both larger and more constricted on the base of its pronotum than the visually similar T. goettingensis (the lesser bloody-nosed beetle).

Its antennae are thick and well segmented, its legs have long tarsi and terminate with a double hook.

The adult beetles usually move slowly on the ground, in the grass and herbaceous plants, mainly at night.

As a defensive behaviour, they exude droplets of their bright red-orange hemolymph by breaking thin membranes in their mouth,[3] which is foul-tasting to predators.

The beetle can be found in southern and central Europe, and is common in Britain and Ireland.