They belong to a beetle of, as nearly I can determine, the genus Ceruchus. Believe it or not, the beetle is harmless and rather small. It might be able to pinch, but unable to break the skin. It appeared on my moth sheet a couple of nights ago. I used my macro lens to get an ant's eye view.
More jaws, this time working ones on a mantisfly. Last year's mantisflies were green with a yellow dorsal stripe. This year's crop are black with yellow spots on the abdomen. Go figger. A mantisfly looks like a cross between a lacewing and a mantis with a length of maybe an inch. It flies to lights and dines on smaller insects. To a mantisfly a lighted moth sheet is a dinner table with goodies like midges and micromoths.