173 



single brood in the north, while there are 

 two in the south. 



The color of the cocoon seems to be in- 

 fluenced in some way by the kind of food 

 eaten by the larva. Cocoons made by 

 larva which have been fed on hickory 

 leaves have a darker color. In the true 

 silk worm mo^h this same influence has 

 been noticed; larvae fed upon the vine 

 producing red cocoons, on lettuce emer- 

 ald green cocoons, while those fed upon 

 white nettle produce yellow, green or vio- 

 let cocoons. It is necessary in order to 

 procure these results, that the larvae be 

 fed upon the mulberry till about twenty 

 days before the formation of the cocoon. 



Polyphemus. The life history of this 

 native silk worm (Telea polyphemus) is 

 by far the best known, because many 

 years ago it was very carefully studied 

 with the hope that it would prove an im- 

 portant silk insect. This hope unfortu- 

 nately has not been realized. 



The moths, as shown by the plate, are 

 really beautiful ; the large eye spots on 

 the hind wings contributing much to- 

 wards this effect. The transparent, win- 

 dow-like centers in the eye spot are also 

 of quite rare occurrence among our 

 moths. These transparent areas do not 

 possess the very minute scales found on 

 the other parts of the wing. Almost all 

 of the wonderful variety of colors found 

 in the wings of butterflies and moths are 

 due either to coloring matter in these 

 scales, or to the breaking up of the white 

 light by minute lines on these scales, such 

 as are seen in the play of colors on a 

 soap-bubble. These fine lines on the 

 scales are only on the upper side, and are 

 about one-sixteen-thousandth of an inch 

 apart. 



The eggs of Polyphemus are very 

 much flattened, about the size of those of 

 Cecropia, and are deposited on leaves and 

 twigs singly or in small groups. These 

 hatch in about ten days and usually in the 

 morning. The young larva often devours 

 the shell which a few moments before af- 

 forded it shelter. This larva feeds upon 

 oak, hickory, apple, maple, elm and a va- 

 riety of other trees, and thus has a larger 

 range of food plants than the Luna larva. 

 The rate of growth is prodigious, as has 

 been shown by Mr. Trovelot. When the 



larva hatches it weighs about one-twen- 

 tieth of a grain ; in ten days it weighs one- 

 half of a grain, or ten times its original 

 weight ; in twenty days it weighs three 

 grains, or sixty times its original weight ; 

 when a month old it weighs thirty-one 

 grains, or six hundred and twenty times 

 its original weight, and has consumed 

 about ninety grains of food ; after fifty 

 days it weighs two hundred and seven 

 grains, or over four thousand times the 

 original weight. At fifty-six days the 

 larva has eaten eighty-six thousand times 

 its original weight in food ! It is there- 

 fore not surprising that these larvae can 

 often be easily detected upon trees by the 

 larsre number of leaves which thev have 

 devoured. 



To provide for this great change in 

 size, the larva moults five times, but the 

 time between these moults is not always 

 the same ; there is usually about ten days 

 between the first four moults and about 

 twenty between the fourth and fifth. The 

 larva stops eating a day before the moult, 

 spins a few threads upon the leaf to which 

 it attaches its hind legs, and waits for the 

 transformation, which usually takes place 

 in the afternoon. The larva, when ma- 

 ture and ready to spin its cocoon, is about 

 three inches long. It is sometimes in- 

 fluenced in its color by the food plant; 

 the normal larva being of a golden green, 

 although it has been known to show more 

 yellow coloring when found on red 

 maple. 



A short time before beginning its 

 cocoon the larva ceases to eat and selects 

 a place for its cocoon. These cocoons are 

 usually found upon the ground among 

 the leaves, but are frequently attached to 

 twigs. After about a half day's work the 

 larva spreads over the inside of the 

 cocoon a gummy, resinous substance, 

 which binds together the threads. After 

 four or five days more of almost contin- 

 uous work, another coating is smeared 

 over the inside, which renders the cocoon 

 practically air-tight. The silk fibres be- 

 come considerably finer as the cocoon 

 nears completion and the supply of sins- 

 begins to run low. For this reason the 

 inner layers of the cocoon are only about 

 half as strong as the outer ones. The 

 larva, as the supply of silk diminishes in 



