This turned up recently in a newspaper report of a study into the probable number of living species. It was said to be a person who studied beetles. Up to a point, Lord Copper. The usual term for a beetleologist is coleopterist (from a Greek word that means sheath-winged), so carabidologist must mean something else.
Finding what it really meant required some minor delving, as it doesn’t appear in any of my dictionaries, not even the huge Oxford English Dictionary, and it’s clearly a specialist term even among beetle researchers. A carabidologist studies carabids, a large and diverse family of mainly nocturnal predatory ground beetles that includes bombardier beetles, sand beetles and tiger beetles. All carabids are beetles, but by no means all beetles are carabids.
If you relied on its etymology for help, you would be left utterly confused. Carabid is said by various dictionaries to derive from Latin cārabus. We can ignore its sense in late Latin of a small ship (which has bequeathed us caravel, a small, fast Portuguese or Spanish ship of the fifteenth to seventeenth centuries). The Latin meaning from classical times given in the dictionaries — a sort of crab, crayfish or crustacean — leaves us scratching our heads. Works of a more specialist nature help by pointing out that cārabus came into Latin from a Greek word that could mean either a spiny lobster or a horned beetle (it seems that neither Greeks nor Romans were hot on detailed species identification).
Carabid has no link with scarab, though that’s indubitably also a beetle; several centuries ago the latter was a vague hand-waving term in English for any insect that was presumed to breed in dung.