The hermit crab is a fantastic creature that wanders with a shell on its back and hides in the shell when it is in danger. It can live carefree through the protection of the hard shell. Over about 800 hermit crab species have been recorded. Most of them live in the ocean and Coenobitidae is the only terrestrial family. Coenobitidae is not a huge family. It only has two genera, of which there’s only one species of Birgus, coconut crab, the largest terrestrial invertebrate. There are 17 species of Coenobita, distributed widely on tropical and subtropical coasts and islands around the world.
The carapace of the terrestrial hermit crab is hard. The breastplate is very soft, asymmetrical and dextral. The terrestrial hermit crab has two chelipeds and the left cheliped is always bigger than the right cheliped. The first and second pair of its pereopods are developed. The third and fourth pair of its pereopods are obviously degenerated. The barb at the tail on the abdomen of the male hermit crab can hook onto the shell. Besides the barb at the tail, the female hermit crab has three ovigerous appendages on the left side of the abdomen. The terrestrial hermit crab is an omnivorous animal, feeding on various animal and plant-based food. These crabs gather in groups to take large food. Shelling Is required for the growth of the terrestrial hermit crab, just like crabs. The shelled hermit crab needs a bigger shell because it becomes bigger, so it must change shells numerous times. The shell is a very important resource for the terrestrial hermit crab and it can be reused by other terrestrial hermit crabs. Catadromy is required for all terrestrial hermit crabs. Their eggs are hatched into planktonic larvae. After shelling and metamorphosis, the larvae find a small shell in the ocean and land on the shore to live there.
Four terrestrial hermit crab species perch in the Taijiang National Park. The external part of terrestrial hermit crabs looks very similar, and they hide entire in the shell when in danger with a part of the chelate revealed. It’s hard to distinguish the species for most people. Basically, it is easy to identify these four species by the characteristics of the chelate and the body color. For Indos hermit crab (Coenobita brevimanus) (Fig. 1), no bristle is available on the upper margin of its chelate palms (left chelate). The color of the Indos hermit crab is purple, purple red or dark red. Regarding Tawny hermit crabs (Coenobita rugosus) (Fig. 2), bristle is available on the upper margin of its chelate palms. There is a row of slanting short ridges on the top of the external side of the palms. The body color of the Tawny hermit crab varies largely, including gray white, light green, pink, light orange or gray blue. Regarding the Concave hermit crabs (Coenobita cavipes) (Fig. 3), bristle is available on the upper margin of its chelate palms. No ridge is available on the external side of the palms. The first antenna is dark brown. The body is olive green or gray brown. Regarding the Komurasaki land hermit crabs (Coenobita violascens) (Fig. 4), bristle is available on the upper margin of its chelate palms. No ridge is available on the external side of the palms. The first antenna is orange red. The adult body is blue purple. Land hermit crabs perch in the area between the flood zone of sandy beaches and maritime forests. The rest of the tree species perch in maritime forests. Komurasaki land hermit crabs often perch in mangroves.
The terrestrial hermit crab faces four kinds of threats, namely exploitation and destruction of its habitat, road killing, being captured as pets, and being used as baits. The number of terrestrial hermit crabs dropped sharply in the past decades. The coast and island for terrestrial hermit crabs to perch are exploited and destructed massively due to population increase and tourism. The habitat decreases day by day and the existence of the terrestrial hermit crab is threatened. The development of coasts and islands has led to an increased number of highways. Many terrestrial hermit crabs have been killed by cars on the coastal highway due to huge traffic. Their cute look and funny behavior brought disaster to the crabs, too. People like to keep them as pets. Lots of them have been caught and sold, which is devastating for them. In addition, anglers often use them as baits, which is a further calamity to them. Terrestrial hermit crabs need their shells for protection, hence they are under a double threat. Cars would crush the shell. After terrestrial hermit crabs are brought to the urban area for sale, it’s difficult to return the shells to the habitat in the wild. Anglers crush their shells to use them baits. Thus, their shells cannot be reused and the number of shells in the wild decreases gradually. The young terrestrial hermit crabs cannot find shells. This reduces the chance of a population recovery.
The terrestrial hermit crab is a lively animal. We should cherish its cute look, funny behavior, and unique lifestyle. We should change ourselves by not capturing or keeping them as pets or picking up shells. Their habitat must be preserved for them to live carefree in the natural habitat. That’s the best way to love them.