DEFENSES OF THE LESSER ANIMALS. 485 



wise be an easy prey and a palatable food. In the condition of the 

 apparently lifeless and really helpless egg, they are covered by their 

 obscurity and littleness, or by being deposited in holes and cracks, or 

 covered with slime or hairy or silken veils and cocoons, under which 

 they escape all but the sharpest search and rare accidents. 



More curious are the many-sided and diversified means provided 

 for the security of the young insect during the helpless larval condi- 

 tion. In this state, when it is destitute of eyes and wings, it is either 

 furnished with hairy bristles or spiny envelopes, like those of numer- 

 ous caterpillars, or with covers composed of fine chips, bud-scales, or 

 other fragments, compactly woven together with a few threads of silk ; 

 or else it is screened from the sun and from parasites and birds by a 

 plaster of mud. A group of insects, described sometimes as sack- weav- 

 ers or sack-moths, make a kind of sack or pocket out of fragments of 

 leaves and splinters, within which they perfect their growth. The 

 case-moths make thick and close-fitting garments for their bodies, out 

 of leaves loosely strung together, within which they hang, head down- 

 ward, from the skeletons of the leaves they have attacked, undistin- 

 guishable to birds and parasites from a long bud-scale or from a dry 

 splinter ; and clothes-moths conceal themselves in similar cases made 

 from the hair-dust or wool of the fabrics of which they have taken pos- 

 session. Some beetles envelop themselves and go through their changes 

 in balls of earth within which they inclose themselves. The larvae 

 of one group protect themselves by a kind of foam which they manu- 

 facture from the juice of the plants they suck. The woolly aphides are 

 well cared for with the great tufts of wool with which they are pro- 

 vided, under the cover of which they suck the juices of plants and 

 bring forth their multitudinous offspring, which given to the winds, 

 the same hairy envelopes serve them as sails on which they are borne 

 afar to new plantations. A species that feeds on the ash-tree takes 

 possession of the galls that form upon it, and can not be removed with- 

 out taking off the whole limb, for birds will not attack insects thus 

 protected. These and other aphides, which are particularly injurious 

 to fruit-trees, are so carefully protected against the ordinary attacks 

 of external enemies that man is left to contend against them alone. 

 The bark-lice or scale-insects are particularly difficult to reach, and 

 seem to multiply in perfect security against all ordinary attacks. 



A whole series of gall-insects provide security for their posterity 

 by colonizing them in the swellings or knots that are produced on the 

 trees wherever they sting the bark and lay their eggs. The larvro, con- 

 tinuing to irritate the tissues of the tree, cause the knots to swell and 

 grow correspondingly with their own growth, and thus find themselves 

 in a well-fortified home exactly fitted to their wants. Within the 

 galls, the naked, helpless worms are at once protected from exterior 

 assaults of every kind and provided with an unfailing supply of food 

 which they can reach without effort, so that their development goes 



