GENERAL INTRODUCTION. 29 



deposit two or three eggs together, but sometimes lay twenty 

 or more in one clump. The Pine Hawk-Moth of Europe 

 {Sphinx pinastri) lays its eggs in small masses, and in this 

 case, as in Celerio euphorbias, the larvae may occur locally 

 in great numbers. When the eggs are laid in masses the moth 

 presumably settles on the food-plant for the operation. 



The egg is usually whitish when first laid, but soon assumes 

 its normal colour, which again changes to pale yellow as the 

 larva forms inside it. The eggs hatch in a period varying 

 from five to ten days or more, the larva biting its way through 

 the shell with its mandibles. The hole thus made is round 

 and is usually situated on one side of the egg. In most 

 species the horn of the newly-hatched larva is movable in 

 a vertical plane and is frequently raised and lowered as the 

 larva moves about. The power to move the horn gets less 

 in later instars, and is usually lost entirely except in the case 

 of a few species in which the horn remains thin till maturity. 

 The larva usually eats a portion or all but the base of the 

 egg-shell soon after emerging, before eating any of the food- 

 plant, arid it will usually suck up a drop or two of water with 

 avidity if it finds any. In some of the species, such as 

 Polyptychus trilineatus, in which the head becomes triangular 

 in the second instar, it eats nothing but the egg-shell until 

 after the first moult, but usually, after resting for a time 

 stretched along the midrib or a vein on the underside of 

 a leaf, it starts to feed. It often punctures small holes in the 

 middle of the leaf before eating from the edge. After feeding 

 for a few days it rests for a day or two preparatory to moulting, 

 often spinning a pad of silk for the prolegs and claspers to get 

 a firm hold. The new and larger head can be seen forming 

 behind the existing head, and the old, now empty, head-case 

 is pushed forward until the skin parts at the neck, rupturing 

 first near the throat, last at the occipital sinus. The skin 

 is worked backwards by an undulatory motion of the body 

 until it reaches the claspers and is shed, the case of the old 

 head remaining attached to the mouth-parts of the new head 

 until removed by being rubbed against some object. Most 

 species eat the cast-off skin. After resting for a time, to allow 

 the new skin to harden, the larva starts feeding again until 

 the next moult is due. Usually there are four moults before 

 the larva is full-fed, though a larger number of moults have 

 been noticed. There is often an extra moult in those species 

 which assume a triangular head in the second instar. 



When about to pupate, the larva stops feeding and rests for 

 about twenty-four hours, during which time the colour becomes 

 darker or the dorsum becomes suffused with brown or reddish. 

 It then leaves the food-plant and wanders about in search 

 of a suitable place to pupate. It hurries along with an 



