Discover the unusual

Social animals often gather to protect or mate or to capture larger prey, but at a University in California, Berkeley, a biologist has noticed hermit crabs There is a self-service social agenda: to push other hermit crabs out of its shell and move to a wider 'home'. According ScienceDaily, October 26, 2012.

All hermit crabs (also known as lizard snails) are suitable for snail shells to make houses for them, but dozens or a similar number of these creatures are on land - those Common ornamental creatures - are the only species that hollows out and remodel their shells, sometimes doubling the volume inside. This will provide more space to grow, more 'rooms' for eggs - sometimes thousands of eggs - and a lighter 'house' to drag around when they fight.

'But the empty shells are very rare on land, so the best hope of moving to a new' home 'is to push others out of the repaired shells , ' said Mark Laidre, a biologist. The school reported this unusual behavior in Current Biology this month.

When three or more hermit crabs gathered, they caught the attention quickly, dozens of others eager to exchange. They often form a 'conga' line, from the smallest to the widest, each clinging to the hermit crabs before it, and when a hermit crab unfortunately slips out of its shell, while moving move into larger ones.

'The hermit crab has been pulled out of its shell often away with the smallest shell, which this shell cannot really protect , ' says Laidre of the Intergrative Department of Biology. 'Then it can be eaten by other animals'.

Laidre said the unusual behavior of hermit crabs is a rare example of how to develop to take advantage of individual appropriateness, in this case, the land against the ocean, leading to a product Surprise side: socialization in a creature that often lives alone.

'Regardless of how precise the hermit crabs modified their shells, they illustrate an important fact about evolution: animals that change and repair their habitats around them. throughout the history of life '. Biological evolutionist Geerat J. Vermeij, UC Davis University wrote in a comment on ScienceDaily.

For decades, Vermeij has studied how animal behavior affects their own evolution - what biologists call 'proper structure' - contrary to popular opinion. Darwin's environment impacts on evolution through natural selection.

'Organisms are not just passive pawns that depend on the selective' whim 'of enemies and allies, but they also actively participate in creating and modifying internal conditions as well. as conditions outside of life ' , Vermeij concluded.

Laidre did his research on the Costa Rica, Pacific coast, where millions of Coenobita compressus hermit crabs can be found along tropical beaches.

Most of the 800 or so hermit crab species live in the ocean, where empty shells are very popular.

However, on the ground, the shells are only from the sea due to the wave being washed up to the shore. Their rarity and the fact that some land predators can smash these shells to catch hermit crabs are probably the reason for the hermit crabs to repair their shells to make them lighter and more spacious, Laidre said.

The importance of repaired shells became apparent after an experiment in which Laidre pulled the hermit crabs out of their shells and instead provided them with a new empty snail shell. But no children survived. He said: 'It is clear that only the smallest hermit crabs will take advantage of the new shell, even if it fits inside the unmodified shell, it still has to extend the time and energy to empty it. shell, and this is one thing that hermit crabs at all sizes want to avoid if possible ".

This work is funded by the Miller Institute of UC Berkeley.