260 MEANS OF DEFENCE OF INSECTS. 



how large a portion of them during this state cease to 

 be locomotive, and assume an appearance of death a . In 

 this helpless condition, unless Providence had furnished 

 them with some means of security, they must fall an easy 

 prey to the most insignificant of their assailants. But 

 even here they are taught to conceal themselves from 

 their enemies by various and singular contrivances. 

 Some seek for safety by burying themselves, previously 

 to the assumption of the pupa, at a considerable depth 

 under the earth ; others bore into the heart of trees, or 

 into pieces of timber ; some take their residence in the 

 hollow stalks of plants ; and many are concealed under 

 leaves, or suspend themselves in dark places, where they 

 cannot readily be seen. But in this state they are not 

 only defended from harm by the situation they select, but 

 also by the covering in which numbers envelop them- 

 selves ; for, besides the leathery case that defends the yet 

 tender and unformed imago, many of these animals know 

 how to weave for it a costly shroud of the finest materials, 

 through which few of its enemies can make their way; 

 and to this curious instinct, as I long since observed, we 

 owe one of the most valuable articles of commerce, the 

 silk that gives lustre to the beauty of our females. These 

 shrouds are sometimes double. Thus the larvae of cer- 

 tain saw-flies spin for themselves a cocoon of a soft, 

 flexible, and close texture, which they surround with* 

 an exterior one composed of a strong kind of net-work, 

 which withstands pressure like a racket b . Here nature 

 has provided that the inclosed animal shall be protected 

 by the interior cocoon from the injury it might be ex- 

 posed to from the harshness of the exterior, while the 

 a VOL. I. 64 Reaum. v. 100. 



