These huge black beetles (about 3cm long) are surprising to find. They look formidable, and will bite if pressed, but prefer to run away and hide under things. I found this one under my garbage can.
This key at the entomology department of the University of Florida keys this as a Pasimachus floridanus, but bugguide.net does not even have that species, suggesting that P. floridanus is now a subset of P. subsulcatus, so all I can safely say about it is that it’s a member of the genus Pasimachus. The photo below left, when I tried to identify it, came back as possibly being P. sublaevis, so who knows. (This is a different individual than the one above, and a different individual than the photo below right.)
Pasimachus beetles are wingless, with their elytra fused into a single hard protective shell. They live in and around leaf litter, eating caterpillars, crickets, and basically anything smaller than themselves. They are formidable ground-based predators, apparently making popular pets because they “tear apart” prey entertainingly (for the humans watching).