There’s a small, iridescent crustacean you might have heard of: its powerful punch can crack holes in aquarium glass and be deployed at the speed of a bullet. These aggressive critters – called mantis shrimp – can also be trigger happy, keen to pummel prey, predators and even their own kind if the need arises.
So how old do offspring have to be to unleash blows? Pretty young it turns out. Mantis shrimp larvae can bludgeon their dinner nine to 15 days after hatching, researchers have found.
For decades, researchers have investigated how this ferocious punch differs between the 400 species of mantis shrimp, but how old they needed to be before they deploy their deadly weaponry was still unclear, said the study’s lead author, Jacob Harrison, from Duke University.
Mantis shrimp are typically divided into two categories: “spearers” brandish claws lined with barbed tips to stab soft-bodied prey such as worms and fish, while “smashers” wield club-like appendages – powered with a spring-like mechanism – to hammer hard-bodied animals such as snails and crabs into submission.
Armed with high-speed, high-resolution cameras, the researchers observed larvae behaviour of a smasher species located in Hawaii. Some eggs were also retrieved, but they hatched in transit to Duke University – so Harrison nurtured the youngsters in the lab.
Once hatched, offspring underwent a number of larval stages. By the time they were three to five millimetres long – about the size of a grain of rice – the larvae had developed an “incredibly large repertoire of appendages relative to their body size”, said Harrison. “We wanted to get a better understanding of what these appendages were being used for. Is this the same type of spring mechanism as the adults … and how does this mechanism operate when [the animal] is this tiny?”
The authors found that the appendages were remarkably similar to those in the adults, just scaled down. Although mathematical models predict that when this spring mechanism gets tinier – the smaller body mass should produce higher acceleration – the larvae didn’t punch above their weight, explained Harrison.
It turns out the young ones punch roughly on a par with the adults, he said. “Which is incredibly amazing for something that small, but it wasn’t exactly as high as we expected.”
The larval strikes were five to 10 times faster than the reported swimming speeds of similarly sized organisms and more than 150 times faster than the shrimp species that the mantis shrimp larvae fed on during the experiments, study authors wrote in the Journal of Experimental Biology.
These larvae are already able to move fast enough to capture their prey, said Harrison. “So, perhaps there’s no selective pressure to get faster.”