SILK-PRODUCING INSECTS. 421 



The well-known Goat-moth is, next to the death's-head moth, one of the largest of the 

 British Lepidoptera, its body being thick, stout, and massive, and its wings wide and spreading. 



Some readers may perhaps have observed certain large, round holes in the trunks of trees 

 into which a finger can be readily thrust, and out of which an empty chrysalis case often 

 projects. These are the burrows made by the caterpillar of the Goat-moth, and often are very 

 destructive to the trees. The larva itself is but little smaller than that of the death's-head 

 moth, and is by no means an attractive-looking creature. Its body is smooth and shining, mostly 

 of dull mahogany-red tinged with ochreous-yellow, and having a large oval patch of chestnut 

 on the back of each segment. It is gifted with a curiously wedge-shaped head, and its mus- 

 cular power is enormous, as may be proved by actual experiment during the life of the creature, 

 or inferred from the marvellous arrangement of muscles which are made visible upon dissection. 



It exudes a liquid of powerful and fetid odor, thought by some to resemble the unpleasant 

 effluvium exhaled by the he-goat. Its influence extends to a considerable distance, and a 

 practised entomologist will often detect the presence of a Goat-moth caterpillar simply by the 

 aid of the nostrils. In spite, however, of the repulsive aspect and unpleasant odor, this 

 creature is thought to be the celebrated Cossus of the ancients, a grub which was found on 

 trees, and, when dressed after some particular fashion, was looker! upon as a very great 

 dainty. 



A much smaller moth, the Wood Leopard, is a very prettily-marked insect, though 

 without the least brilliancy of color. The caterpillar of this insect feeds upon the interior of 

 many trees, seeming to prefer the wood of the apple, pear, and other fruit-trees. It is a naked, 

 fleshy-looking larva, of a light yellow color, and having a double row of black spots upon each 

 segment. Like the goat-moth, it prepares a cocoon-like cell when it is about to take the pupal 

 form, but the lining is of stronger materials, cemented firmly together with a glutinous sub- 

 stance secreted by the insect. The moth is seldom seen until July, and is tolerably plentiful 

 in some places, appearing to be decidedly local and rather intermittent in its visits. 



The family of the Bombycida? includes several insects of inestimable value to mankind, 

 the various silk-producing moths being included in its ranks. The common silk-worm is the 

 most useful of all of them. The accompanying oleograph is a true illustration of this familiar 

 insect. The valuable results of its habits are too well known to need any description. But as 

 it is not generally known that upwards of forty silk-producing moth's exist in different parts 

 of the world, a short history will be given of some of them, together with a brief description of 

 on9 of the finest species. 



All these insects secrete the silk in two large intestine-like vessels in the interior, which 

 contain a gelatinous kind of substance, and become enormously large just before the cater- 

 pillar is about to change into a pupa. Both the silk organs unite in a common tube at the 

 mouth, technically called the spinneret, and through this tube the semi-liquid is ejected. As 

 soon as it comes into contact with the air it hardens into that soft, shining fibre with which 

 we are so familiar. If a single fibre of silk be examined through a good microscope, it will be 

 seen to consist of two smaller fibres laid parallel to each other, like the barrels of a double 

 gun, this structure being due to the double secreting vessels. The goodness of silk chiefly 

 consists in the manner in which these semi-fibres are placed together. Silk-worm "gut," as 

 it is called by anglers, is made by steeping the caterpillars in strong vinegar for a time, and 

 then pulling them suddenly until they elongate into the well-known threads to which hooks 

 are attached. 



The caterpillar employs the silk for the purpose of constructing a cocoon in which it can 

 lie until it has assumed the perfect form ; and proceeds with wonderful regularity and dispatch 

 in its work, its head passing from side to side, always carrying with it a thread, and the cocoon 

 being gradually formed into the oval shape which it finally assumes. The few outermost 

 layers are always rough and of poor quality ; these are stripped off, and the end of the thread 

 being found, it is fastened to a wheel, and spun off into a hank of soft yellow fibre. The 

 coloring matter is very variable, sometimes being hardly visible, and at others giving the silk 

 a bright orange tint. It fades much on exposure to light. 



