Are crabs actually fatter during full moon?

If you’ve ever followed your mom/grandma/whoever to the local pasar pagi for groceries, chances are, you’ve heard them say, “Full moon tonight, good day to buy crab ah!”

And you never think to question it, because it’s just one of those things older people tell you, like “If you don’t finish your rice, next time your wife will have a lot of pimples”. Absolute hogwash. This writer eats every single rice on all his plates, and his wife still got pimples.

But what if we told you there’s actually science to back the crab thing? As it turns out…

Crabs do have better flesh… during the NEW moon

That’s right, new moon, NOT full moon. In case you don’t know your moons, full moon is when the moon is round and bright, and new moon is when you can’t really see much of the moon, if at all.

So, a paper published in 2019 by a scientist duo from Universitas Muslim Indonesia details how they found out that mud crabs are at their thiccest in the full moon phase. Long story short: they got a bunch of crabs and measured the levels of haemolymph ecdysteroid in those crabs in each moon phase.

“What’s haemolymph ecdysteroid?”, I hear you ask. It’s a hormone that determines when crabs moult (that’s when they shed their old shells to grow a bigger shell).

They found out from the experiment that the levels of haemolymph ecdysteroid were at its lowest during full moons and new moons in the mud crabs – which was when they’d just shed their old shells. More importantly, they noted that 70-80% of mud crabs caught during the new moon have ‘a full, fleshy body’, as opposed to the watery flesh of the crabs during full moons.

And hey, if you don’t believe these nerds from Indonesia…

Ex-fishermen we talked to also said it’s better to buy crabs during new moons

One of the ex-fishermen – who is this writer’s dad, by the way – speculated that crabs have developed watery flesh in full moons as an evolutionary method to help them avoid predators better, cuz predators can ‘see’ better during full moon nights. Another ex-fisherman we talked to didn’t have an explanation, and only said that ‘bulan baru’ is when crabs have the most flesh.

If y’all wanna test the theory out, y’all can download one of those moon phase apps, buy some crabs, and let us know if it’s true.