HOW TO KNOW THE IMMATURE INSECTS 



3. Coarctate (Fig. 34). — The appendages are not visible 

 at all and are obscured by the larval skin before the 

 last moult, in the coarctate pupa. This type is found 

 in the more specialized Diptera (Cyclorrhapha) and 

 in certain Coccidae and Stylopidae. 



The length of time in which an insect remains in 

 its pupal state is highly variable. Much goes on within 

 the pupal case before the adult is ready to emerge but 

 the whole process moves so rapidly with some species 

 that the insect remains as a pupa for only a few days. 

 Many insects pass the winter or other unfavorable 

 time in the pupa stage. When their growth is com- ^^9-^ ^agSt^^Hy- 

 pleted many larvae travel for a day or two thus scat-'^^y'^^g^'*'**'*'***® 

 tering the species and lessening the chances for total 

 loss of a brood. These larvae usually select some pro- 

 tected spot before settling down. 



PROTECTION OF PUPAE. — Most pupae are concealed in one way 



or another from their enemies, and 

 also from such adverse influences 

 as excess of moisture, sudden mark- 

 ed variations of temperature, shock 

 and other mechanical disturbance. Pro- 

 vision against such influences is usual- 

 ly made by the larva in its last instar. 

 Many lepidopterous and coleopterous 

 larvae burrow beneath the ground and 

 there construct earthen cells in which 

 to pupate. The larger number of insects, 

 however, construct cocoons which are 

 special envelopes formed either of silk 

 or of extraneous material bound togeth- 

 er er by means of threads of that sub- 

 stance. Thus many wood-boring larvae 

 utilize chips. Larvae which transform 

 in the ground select particles of earth. 

 Many Arctiid larvae use their body- 

 hairs and Trichoptera use pebbels, veg- 



Rig. 35. Cocoons: a, braconid 

 cocoon; b, empty braconid co- 

 coon; c, cocoon of the clover- 

 leaf weevil; d, cocoon of the 

 aphid lion. (U.S.D.A.) 



18 



