[Pictured: an unusually LARGE coconut crab! (Birgus latro)]
Not all crabs have edible meat in both the bodies and the claws, and just as there is "light" and "dark" meat in a chicken or turkey, there is light and dark meat in crab.
The claws have white meat, which tends to be sweeter/lighter, the bodies have brown, which tends to be richer. Males have more white meat because they have larger claws (female crabs are called "hens", male crabs are called "cocks" and have narrower tails and larger claws, females have broader, somewhat heart-shaped tails).
While not ALL crabs are safe to eat, only relatively few carry lethal doses of toxins. NOTE: if something is toxic enough, it's considered poisonous. “Poison” implies a high level of toxicity, though any substance is technically poisonous if taken in a large enough dose. Poison always refers to biological organisms, whereas “toxic” can refer to biological organisms AND non-biological substances.
Most of the toxic crabs belong to a genus called “Xanthidae,” a family of crabs known as mud crabs, pebble crabs or rubble crabs. Xanthid crabs are often brightly colored and can accumulate two of the most lethal natural substances known in their muscles and egg masses which are poisonous and “heat stable”, or not destroyed by cooking, and there is no known antidote (as little as half of a milligram is capable of killing an average sized adult!).
The toxins are similar to the tetrodotoxin and saxitoxin. Tetrodotoxin is found in the Japanese puffer fish, a delicacy known as “fugu” which only licensed chefs are allowed to prepare. Saxitoxin is the primary toxin involved in paralytic shellfish poisoning, which is often caused by people eating mussels or oysters that have consumed toxic algae. It’s also listed as a grade one chemical weapon under the UN Chemical Weapons Convention and was reputedly used by the CIA in suicide pills.
Both chemicals are neurotoxins, affecting the nervous system, resulting in paralysis by shutting down the nerve cells’ ability to transmit information.
So far, only a small number of species of this family are known to be toxic, but it's a good idea to avoid eating them regardless. These crabs are not truly poisonous and the crabs do not produce the toxins themselves, and some species are not always toxic, so it's likely the toxins are obtained through the crab’s feeding or by symbiotic bacteria.
In any case, all crabs are scavengers, and one wild food rule to remember is things tend to taste like what they’ve been feeding on. If a crab has been feeding on coconuts, papayas or other crabs, that’s what they’ll taste like. But if they’ve been feeding on carcasses, garbage or sewage, you need to PURGE them first. So after you’ve caught them, confine them and feed them something good to eat for at least a few days. The more disgusting their feeding habit, the more days you should purge them, but up to a week should be plenty. And yes, the coconut crab in the picture was DELICIOUS! 😉
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