APPENDIX. 55 



Those of the Hymenoptera (e.g., sawflies, wood wasps 2 etc.) 

 have six, eighteen, or twenty-two appendages, and in sawfly larvae 

 the second abdominal segment always has a pair of pseudopcds, 

 in some cases (wood wasps) the limbs are vestigal, while in other 

 cases they are absent. 



The larval stage is usually the one in which the insect does 

 the greatest amount of damage; they feed voraciously, the daily 

 consumption of food often exceeding many times the weight of the 

 larva. With a plentiful supply of food they rapidly increase in 

 size, and, as the chitinous skin is only capable of a limited expan- 

 sion, it ultimately splits, and the larva comes out with a new^ and 

 sometimes differently-coloured, skin. This process, known as 

 moulting, usually takes place five times, but the number is variable; 

 2 ' 3- 4' 5- 7 IO > I! > I2 > an d even 20, 25, and 30 moults are known in 

 different insects. The larva is now said to be full-fed, and it 

 changes to a pupa or chrysalis. 



The duration of the larval period is subject to much variation; 

 sometimes it is only a few days, while in other cases it may last 

 for months or even years. 



The Pupa. The full-fed larva generally either buries itself 

 in the ground (Rose Chafer), forming a cell of earthly particles, or 

 spins a silky cocoon 'Codling Moth), in which it changes to the 

 pupal condition. After a time the pupal case containing the insect 

 cracks or splits, and the perfect insect or imago creeps out. 



The Imago. This is the fully-formed insect, and may be 

 described as an animal consisting of thirteen segments, breathing 

 "by tracheal tubes, with a single pair of feelers, and having the 

 body divided up into three distinct regions head, thorax, and 

 abdomen the three segments of the thorax each carrying a pair 

 of jointed legs. 



On reaching the imago stage, the pairing of the sexes is soon 

 effected ; the female then lays her eggs, and shortly afterwards dies, 

 the generation or life-cycle being thus completed. In some cases 

 the perfect insect only lives a few hours or days, but in others they 

 hibernate during the winter, and lay their eggs in the following 

 spring. 



Before the depredations of any particular species of insect 

 can be effectvely dealt with, it is important that all the stages 

 and variations of the life-cycle should be clearly and thoroughly 

 understood. 



