The coconut crab (Birgus latro)

Coconut crabs mate frequently and quickly on dry land in the period from May to September, especially between early June and late August.[28] Males have spermatophores and deposit a mass of spermatophores on the abdomens of the females;[29] the oviducts opens at the base of the third pereiopods, and fertilisation is thought to occur on the external surface of the abdomen, as the eggs pass through the spermatophore mass.[30] The extrusion of eggs occurs on land in crevices or burrows near the shore.[31] The female lays her eggs shortly after mating and glues them to the underside of her abdomen, carrying the fertilised eggs underneath her body for a few months. At the time of hatching, the female coconut crab migrates to the seashore and releases the larvae into the ocean.[30] The coconut crab takes a large risk while laying the eggs because coconut crabs can't swim. If a coconut crab falls into the water or gets swept away, its weight makes it difficult, or impossible, for it to swim back to dry land.[32] The egg laying usually takes place on rocky shores at dusk, especially when this coincides with high tide.[33] The empty egg cases remain on the female's body after the larvae have been released, and the female eats the egg cases within a few days.[33] The larvae float in the pelagic zone of the ocean with other plankton for 3–4 weeks,[13] during which a large number of them are eaten by predators. The larvae pass through three to five zoea stages before moulting into the postlarval glaucothoe stage; this process takes from 25 to 33 days.[34] Upon reaching the glaucothoe stage of development, they settle to the bottom, find and wear a suitably sized gastropod shell, and migrate to the shoreline with other terrestrial hermit crabs.[35] At that time, they sometimes visit dry land. Afterwards, they leave the ocean permanently and lose the ability to breathe in water. As with all hermit crabs, they change their shells as they grow. Young coconut crabs that cannot find a seashell of the right size often use broken coconut pieces. When they outgrow their shells, they develop a hardened abdomen. The coconut crab reaches sexual maturity around 5 years after hatching.[30] They reach their maximum size only after 40–60 years.[18] It grows remarkably slowly, taking perhaps 120 years to reach full size, as posited by ecologist Michelle Drew of the Max Planck Institute.[3