DEVELOPMENT 167 
negative reaction to light (negative phototropism) or a positive 
reaction to contact (positive thigmotropism). 
Exposed, sedentary larve, as those of many Lepidop- 
tera and Coleoptera, often exhibit highly developed protective 
adaptations. Caterpillars may be colored to match their sur- 
roundings and may resemble twigs, bird-dung, etc.; or larvee 
may possess a disagreeable taste or repellent fluids or spines, 
these odious qualities being frequently associated with warn- 
ing colors. 
Larve need protection also against adverse climatal condi- 
tions, especially low temperature and excessive moisture. 
The thick hairy clothing of some hibernating caterpillars, as 
Tsia (Pyrrharctia) isabella, doubtless serves to mollify sudden 
changes of temperature. Naked cutworms hibernate in well- 
sheltered situations, and the grubs of the common “ May 
beetles,” or “ June bugs,” burrow down into the ground below 
the reach of frost. Ordinary high temperatures have little 
effect upon larvz, except to accelerate their growth. Exces- 
sive moisture is fatal to immature insects in general 
conspicu- 
ously fatal to the chinch bug, Rocky Mountain locust, aphids 
and sawfly larve. The effect of moisture may be an indirect 
one, however; thus moisture may favor the development of 
bacteria and fungi, or a heavy rain may be disastrous not only 
by drowning larve, but also by washing them off their food 
plants. 
As a result of secondary adaptive modifications, larvee 
may differ far more than their imagines. Thus Platygaster in 
its extraordinary first larval form (Tig. 218) is entirely unlike 
the larve of other parasitic Hymenoptera, reminding one, 
indeed, of the crustacean Cyclops rather than the larva of an 
insect. As Lubbock has said, the characters of a larva depend 
-(1) upon the group of insects to which the larva belongs and 
(2) upon the special environment of the larva. 
Pupa.—The term pupa is strictly applicable to holometabo- 
lous insects only. Most Lepidoptera and many Diptera have 
an obtect pupa (Fig. 212), or one in which the appendages 
