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Photo#176068
Beach beetle - Scarites marinus

Beach beetle - Scarites marinus
Sunset Beach, Pinellas County, Florida, USA
March 24, 2008
Size: ~11 mm (with mandibles)
Found under a pile of stranded seaweed at the back of a sandy beach.
More info at: http://snailstales.blogspot.com/2008/04/who-preys-on-truncatella.html

not a snail predator
I kept this particular beetle in a dish with small terrestrial snails from its habitat for 1.5 days, but it did not prey on them. Details: http://snailstales.blogspot.com/2008/04/who-preys-on-truncatella.html

Ground Beetle (Carabidae) - genus Scarites
characterized by large black body, impressive mandibles, a narrow waist behind pronotum (thorax).

 
Scarites
S. marinus Nichols.

 
Source for species identification?
Mike, I'm impressed that you're keeping atop BugGuide submissions of carabids (my interest) from the Florida area. As you know, North American Scarites is badly in need of taxonomic revision along with reliable keys to the many confusing species. I see that there are 5 species of Scarites listed in your handy "Distributional Checklist of Beetles of Florida" (1998). I'm curious to learn your criteria for placing image with S. marinus - likely based on a combination of collection site & morphology.

Addendum: Right after sending this note I reminded myself of the article by Nichols (1986) in Proc. Entomol. Soc. Wash. 88(2) which contains new species description of S. marinus and a key to the subterraneus complex. However, this complex does not cover a couple other Floridian Scarites species.

Addendum 2: Antenna segments shown are relatively moniliform (roundish), larger body size (~11 mm), and Gulf Coast sea beach are three important factors cited in the Nichols article that favor S. marinus.

 
Source
Exactly. Those plus the relative smoothness of the elytra. I'm not so daring with all carabids, though.

 
Is this a snail predator?
Is this a snail predator?

 
Scarites does not dine on snails.
All Scarites species favor small insects in adult, immature, or egg form. Menu for some species includes earthworm and young seedlings in field seed beds - but not expected for seaside S. marinus.