In the Isle of France a new building was ruined by these insects in a few months; and at Colombo a large house suddenly fell in over the heads of the occupants, the beams being crushed like egg shells. The work they accomplished in this way would hardly be credited were it not for the substantiated statements collected by the authorities in the countries where they are mostly found. The so-called caddis worms (Fig. 191) are merely the larvæ of the caddis fly which incloses itself in a case that is often decorated in a singular way. The cases of a number of the worms placed together display a striking variety of designs. Some roll up leaves; others spin a silken thread from the mouth and bind pieces of leaves together, attaching other pieces to it. [Illustration: FIG. 191.--Caddis worm and case.] XXII. SOME MIMICS All insects have a continual struggle for life. They constitute the food of many birds, and very few of the young escape these watchful creatures and attain mature life. To enable the insects to escape, nature has given many a strange protective garb, which is called mimicry or a protective resemblance. Sometimes it is color, an insect mimicking a leaf in color; or again, the insect imitates a twig or leaf in shape, and so escapes attention. We find examples of this in many families, but particularly among the insects now under consideration. The mantis (Fig. 192) belongs to a group in which the insects resemble twigs in shape and color, and nothing could be more striking than these strange, slow-moving creatures. They have an uncanny, weird appearance, and look as though they might have been originally of wood. I have seen them in the tropics passing slowly along a limb, lifting one leg at a time, moving it with all the halting deliberation of an automaton; but when the mantis perceived me, it stopped just as it was, the foot that was in the air remaining as though it had been frozen in the act. Some are a vivid green, and in them the resemblance to twigs is very striking. I once encouraged a number to live in my preserves, where I watched and studied and often fed them. They would take a fly from my hand by a very rapid movement of the cruel, fore hands or claws, which were toothed. When food was scarce the insects would devour one another in the most deliberate fashion, then assume the quaint, supplicating position with claws up, from which the insect is called the praying mantis. My specimens deposited their eggs in a curious case about an inch long, resembling a trilobite, which they attached to the fence and colored the exact hue of the latter. The fence was not painted, and varied in color, yet the nests always agreed more or less exactly with the shade or tint of the plank or base to which it was attached. [Illustration: FIG. 192.--The mantis.]