Mantis shrimp wield a spring-loaded appendage that punches through water with explosive force — and their babies can start swinging just nine days after they hatch.

In a new study, published Thursday (April 29) in the Journal of Experimental Biology, scientists studied larval Philippine mantis shrimp (Gonodactylaceus falcatus) originally collected from Oahu, Hawaii. The team also reared some of the same species from eggs, carefully monitoring their development through time and then zooming in on their punching appendage under the microscope.