There are two Việt words for crabs that you might hear frequently, cua and ghẹ, but there seems to be some confusion over the difference. Google Translate unhelpfully renders both of them as “crab” when translating to English. Well, cua refers to crabs in general, and not just true crabs (brachyura), but also the other crab-like crustaceans like hermit crabs (anomura) – if it’s a crab, it’s con cua.
Ghẹ refers to swimming crabs (portunidae) – crabs that have hind legs that are flattened to form swimming paddles. Well-known ghẹ include the ghẹ xanh (portunus pelagicus, the blue swimmer), the ghẹ dĩa or ghẹ đỏ (portunus haanii, the red warty swimming crab), and the ghẹ chấm (portunus trituberculatus). Note that not all crabs with swimming paddles are called ghẹ – a crab must live in the ocean or estuaries and have the characteristic angular carapace and long, narrow claws (chelae) to be called con ghẹ. The mud crabs scylla serrata (cua bùn) and scylla paramamosain (cua xanh) are called cua because they live in fresh water, their claws are large, and their carapaces are rounder.
There are other Việt words for specific kinds of crabs, including rạm or đam (varunidae), dã tràng (sand bubbler crabs), cáy (ocypodidae), cà ra (Chinese mitten crabs), and cúm núm (calappidae, from cua khúm núm, due to the way they appear to hide their faces – Google Translate amusingly renders “cúm núm” as “nipple flu” in English). Like ghẹ, these aren’t strict taxonomic or phylogenetic classifications – they’re common names based on appearance (morphology) and habitat.
Ghệ or ghẹ can also be used informally to refer to women, as in “ghẹ mới của tao” (my new girlfriend), but this is a little vulgar and should be avoided in polite company.
