Dale Brunk, age 11, of Newport News, Virginia, for his question:
Do robber crabs really climb trees?
Most of the crusty crabs belong to the sea and the general rule says that sea dwellers must stay submerged to get thei>= oxygen from the water. However, there are a few exceptions to almost any rule you can mention. The robber crab seems to be one of them. In the first place, he is not encased in a crusty coast. What's more he spends most of his time out of the water and yes, he really can climb a tree.
The robber crab lives on tropical shores where the coconuts grow. He spends his adult life on land, scrounging for food en the beaches. His favorite dessert is coconut meat and the best coconuts grow under the leafy parasols at the top of tall palm trees. Surely they must be out of his reach and perhaps the crab waits until they fall to the ground. Not at all.
He uses his crabby claws to scramble straight up the side of the tall trees. Then he picks himself a coconut and tears off its hairy topcoat. He cracks open the shells and enjoys the nut meat. There is photographic proof that this surprising nature story is true.
When spotted in the light of day, he digs himself into the moist sand or scuttles back to his burrow. He is classed as one of the hermit crabs, whose naked abdomens are not encased in the usual crabby shell. Most of them are merely two or three inches long and protect themselves by tucking their behinds into discarded shells. The robber hermit is a two foot giant with crusty plates on part of his abdomen. Instead of borrowing a discarded shell, he depends on evasive tactics to protect himself.
The 4,400 ten legged crabs belong in the Order Decapoda. They are a group of specialists and come in a vast variety of shapes, sizes and fancy colors. Some species swim out in the deep ocean. Others live their bad tempered lives in tidal pools. Several species live most of their lives on land. The pasty ghost crab spends the day in a sandy burrow and scuttles over the beach at night. When he casts no shadow, he is almost invisible on the pale sand. Many land crabs, rock crabs and sand crabs live out of the water in burrows and secret crevices.' Some live amphibious ones live among the soggy roots of mango swamps. One species lives a mile high in limestone caves around the streams of Borneo. However, all crabs must spend their egg and larva stages submerged in water.
Adult land crabs do not have lungs to breathe air and their gills must extract dissolved oxygen from the water. However, these are arranged to seal themselves in a moist environment. The feathery gills along the sides of the thorax are shielded by protective plates from the drying air. These plumy feathers are riddled with blood vessels that exchange oxygen and carbon dioxide with the trapped moisture.