638 



by Dr T W. Harris, in the Massachusetts Agricul- 

 tural Repository. This insect is the caterpillar of a 

 moth allied to our ermine spot moths, being the 

 Arctia acria of Fabricius. It is very hairy, somewhat 

 like the caterpillar of the garden tyger-moth, and is 

 endued with a great degree of vitality, for long im- 

 mersion in water does not destroy life. Being often 

 exposed to that element, they seem provided with the 

 power of enduring its approaches. They feed twice 

 in the day, about ten o'clock in the morning, and four 

 in the afternoon. If overtaken by the tide while 

 feeding, they mount to the top of the grass, and then, 

 if obliged to relinquish their hold, contracting them- 

 selves into a circular form, they commit themselves to 

 the water. By this means they are washed to the 

 borders of the marsh, where they are left by the wash 

 of the sea in heaps, but alive, and in a short time 

 ready to re-commence their depredations upon the 

 meadows. The hair upon their bodies seems to pos- 

 sess a ivpelling power, which secures the spiracles 

 from the admission or access of the water, for were 

 this to be the case, the insect would be drowned. 

 Their most favourite food is the onion grass, which is 

 very succulent ; but they are not fastidious, and eat 

 with avidity 'fox' and 'bottom grass,' and even 

 ' thatch ' and ' sedge.' By the first of August these 

 caterpillars have attained their greatest size ; they 

 now become very voracious, and continue eating all 

 the day and night without intermission, by which 

 means the hay crops are greatly detrimented. Soon 

 they leave the meadows aggregated in great numbers, 

 and commence their wandering state, or ' begin to run,' 

 as is the phrase, devouring every thing in their pro- 

 gress. Corn-fields, gardens, and even the coarse and 

 rank produce of road sides, afford them temporary 

 nourishment, until they have found a place of security 

 against the tide and weather. Another moth, belong- 

 ing to the same group, of whose proceedings an 

 account was published in 1782, by Mr. W. Curtis, 

 under the name of the brown-tail moth, Porthesia 

 aurijlua, is occasionally not less numerous nor inju- 

 rious in our own country. In the year above men- 

 tioned, so vast were their numbers, that the trees 

 were despoiled of their foliage ; and it was feared that 

 they would extirpate the growing corn and grass, and 

 starve the cattle to death in the fields. They were 

 regarded as the harbingers of the plague, and prayers 

 were ordered to be read in all the churches, to avert 

 the supposed impending calamity. In France, also, 

 the same, or nearly-allied species has so fre- 

 quently appeared in such prodigious numbers, to the 

 defoliation of the forests, that the legislature have 

 promulgated several ordonnances for their destruction. 

 The colours of larvse are very variable ; indeed 

 it would be very difficult to lay down many general 

 rules respecting them. It may, however, be observed 

 that those species which are destitute of legs, and are 

 of a fleshy consistence, have the body generally of a 

 white, or dirty white colour. Many caterpillars also, 

 which greatly resemble each other, produce moths 

 totally unlike, whilst moths, which are so closely allied 

 that it is almost impossible specifically to distinguish 

 them (the shark moths, genus Cucullia, for mstance), 

 are different in their larvae, which are consequently 

 resorted to as affording a more certain specific cha- 

 racter. Caterpillars also vary in their colours during 

 their growth ; and Mr. Sheppard has observed, that 

 the skm of the caterpillar of the privet hawk moth 

 after being under ground four days, was changed 



INSECT. 



rom a vivid green to a dull red. A similar change 



of colour also occurred in a caterpillar of the puss 

 moth (Centra vinula), which we endeavoured to pre- 

 serve. From what has been said, it will be easily 

 jonceived that the colour of the caterpillar affords no 

 criterion for judging of the colours of the future moth : 

 the most beautifully coloured larvae, as Reaumur ob- 

 serves (mem. 1. page 198), producing the dullest 

 coloured moths ; and vice versa. De Geer has, how- 

 ever, given two instances in which the moth preserves 

 the colours of the caterpillar ; these are the magpie 

 moth (Abraxas grossulariatce, figured in our article 

 ABRAXAS), and the green Pyralis prasina. Dr. 

 Harris, in his memoir upon the salt marsh caterpillar, 

 also notices that there are two varieties of the moth 

 corresponding with the caterpillars from which they 

 are produced ; from the dark caterpillar and brown 

 cocoon proceeds a moth with ash-coloured wings, and 

 from the lighter coloured larva and cocoon is disclosed 

 a moth whose upper, and also sometimes the lower, 

 wings are white, these colours not designating the 

 sex. De Geer also observed that the brown cater- 

 pillars of the yellow underwing moth ( Triphtcna pro- 

 nuba) produce males, and the green ones females. 



Respecting the growth and size of larvae, it is to be 

 observed as a general rule, that they are longer and 

 heavier than the perfect insect. According to the 

 Count Dandolo, the following is a statement of the 

 progressive increase in the weight of silkworms. 



Grains 



A hundred worms just hatched weigh about 1 

 After the first moulting . . 15 



After the second moulting . . 94 



After the third moulting . . 400 



After the fourth moulting . . . 1628 



On attaining the largest size . . 9500 



From what we have already advanced in our obser- 

 vations upon the principles of metamorphosis, it will 

 readily be conceived that with this rapid growth a 

 continued shedding of the skin must be required. 

 Hence we find caterpillars are subject to a greater or 

 less number of these changes of the skin. The great 

 garden tyger-moth (Arctia caja) undergoing as many 

 as ten such moultings, Arctia dominula nine, Arctia 

 villica from five to eight. The ordinary number, 

 however, appears to be three or four, although it 

 would seem that the grub of the bee, and many other 

 footless grubs, undergo no moulting, although both 

 Reaumur and Swammerdam assert that the contrary 

 is the case. We have already, in our observations 

 upon the general principles of the metamorphoses, 

 noticed the peculiarities which occur in the caterpillar 

 immediately previous to and during its moulting. We 

 may therefore add, in order to complete the subject, 

 that, quitting its former skin, the caterpillar appears 

 very languid, and its body is soft and easily injured ; 

 it speedily, however, resumes its strength, and has 

 increased so much in size that it appears extraordi- 

 nary how it could have been packed in its former 

 covering ; its wonted voracity returns, and it now 

 feeds with redoubled energy, as if to make up for the 

 time which it had lost. 



In this manner, and for a certain period of time, 

 the growth of the insect is continued. The period 

 which is required for the arrival of the larva at its full 

 size is very variable. Perhaps the most general rule 

 is, that insects are annual in their generations ; either 

 being hatched in the spring from eggs deposited in 

 the preceding autumn, and becoming chrysalides in 



