As Xanthidae poisonous - DO NOT CONSUME (even cooked)!
Touching or even "letting it pinch" are harmless.
It is saxitoxin (STX, a neurotoxin responsible for shellfish poisoning/mytilism among other things, also found in pufferfish), probably ingested by benthic animals or symbiotic bacteria (Ng, 2008).
Thus, similar to poison dart frogs, crabs should lose their toxicity in captivity.
Since the toxin is ingested through food, not all specimens of the species need be toxic or equally toxic.
In specimens caught near Japan, very high toxin levels of 590 micrograms were detected, which would kill over 1,000 people!
1,000 times more poisonous than sarin and cyanide, repeatedly discussed as a chemical warfare agent... One of the strongest poisons ever.
No known antidote.
Saxitoxin can enter the body by inhalation (inhalation) as well as ingestion.
In the case of inhaled saxitoxin, fatal respiratory paralysis can occur within a very short time (minutes).
Non-fatal doses cause the following symptoms in humans after several hours: nausea, vomiting, diarrhea, and abdominal pain.
Those affected may see double vision, and paralysis of the respiratory muscles is evident.
Those who survive 12 hours have a good chance of recovering completely.