52 
STRANGE DWELLINGS. 
barrow, in which it resides, and which supplies it with nourish- 
ment as with a residence. The tunnels which it makes are 
mostly driven in an oblique direction ; so that when a large 
number of these creatures have been at work upon a piece of 
timber, the effect of their united labours is to loosen a flake of 
variable dimensions. As long as the weather is calm, the 
loosened flake keeps its position ; but no sooner does a tempest 
arise, than the flake is washed away, and a new surface is 
exposed to the action of the Chelura. 
When the Chelura is placed on dry land, it is able to leap I 
nearly as well as the sand-hopper, and performs the feat in a 
similar manner. 
This is not the only wood-boring crustacean with which our 
coasts are pestered ; for the Gribble ( Limnoria terebrans) makes 
deeper tunnels than the preceding creature, though it is not so 
rapidly destructive, owing to the direction of its burrows, which 
are driven straight into the wood, and do not cause it to flake 
off so quickly as in the case when the Chelura excavates it. 
Still, it works very great harm to the submerged timber, boring | 
to a depth of two inches, and nearly always tunnelling in a 
straight line, unless forced to deviate by a nail, a knot, or 
similar obstacle. The Gribble is a very tiny creature, hardly 
larger than a grain of rice, and yet, by dint of swarming 
numbers, it is able to consume the wooden piles on which 
certain piers and jetties are supported ; and in the short space 
of three years these destructive Crustacea have been known to 
eat away a thick fir plank, and to reduce it to a mere honey- 
comb. Sometimes these two wood-boring shrimps attack the 
same piece of wood, and, in such cases, the mischief which 
they perpetrate is almost incredible, considering their small 
dimensions and the nature of the substance into which they 
bore. The common fresh-water shrimp, so plentiful in our j 
brooks and rivulets, is closely allied to the Gribble, and will 
convey a very good idea of its appearance. In some parts of 
our coasts the ravages of these animals are so destructive, that 
the substitution of iron or stone for wood has become a necessity. 
