How do these creatures hop? By first doubling up their bodies, and then straightening them out again with a kind of jerk. It is exactly opposite, in fact, to the way in which shrimps and lobsters swim.
Sandhoppers do not follow the retreating tide, but bury themselves in the sand very soon after the waves have ceased to break over them. Even when the surface of the sand is quite dry you can find their burrows by stamping with your foot, when a number of little round holes will suddenly open all round you.
These creatures have wonderfully sharp little teeth, and if you allowed a swarm of them to rest for a little while on your handkerchief you would most likely find that it was full of tiny holes when you took it up. They will eat almost anything, either animal or vegetable, and are quite as useful as the shrimps and prawns in helping to keep the sea-water pure. But they have a great many enemies, for sea-birds, land-birds, crabs, and all sorts of other creatures, destroy them literally in millions.
The Fresh-water Shrimp
This shrimp is very much like the sandhopper in some ways. You may find it in numbers in almost any small stream or rivulet. It hides under stones, or in little crevices in the bank, darting out now and then to seize one of the tiny creatures upon which it feeds, and then hurrying back with it to its retreat. When it is in the water it travels along by a series of jerks; sometimes swimming with its back uppermost, and sometimes on one side. But if it is placed on dry ground it is perfectly helpless, for its legs are not nearly strong enough to carry it, and the only result of its struggles is to turn it round and round in a screw-like manner without forcing it forward at all.
Woodlice
These odd little creatures are really crustaceans, although they belong to quite a different group from that about which you have just been reading. They simply swarm in all damp places. Under logs, in heaps of decaying leaves, and under the bark of dead trees, they are always extremely plentiful, and you may also find them in hundreds in cellars and outhouses. There are several different kinds, one of which rolls itself up into a ball when it is touched or alarmed. This is called the pill-woodlouse, or pill-armadillo. Another one is remarkable for the fact that the mother carries her little ones about with her in a pouch underneath her body for some little time after they are born.
Barnacles
You would hardly think that barnacles were crustaceans, would you? Yet they are; though certainly they are very unlike any of those about which we have been telling. You can find them in countless thousands upon the rocks which are left bare by the tide at low water, and very often the hulls of ships are so covered with them that the vessels have to be taken into dry dock and thoroughly cleaned before they are fit to start upon a voyage.
These animals fasten themselves down to their hold by a kind of foot-stalk, which is firmly attached by a very strong cement. The upper part of the body becomes covered with a shell, consisting of several pieces, or valves; and between these, six odd little limbs can be poked out at will. These limbs are very hairy, and are always waving about, so as to sweep into the mouth any tiny scraps of food which may be floating in the water.