60 THE LIFE-STORY OF INSECTS [CH. 



dense hairy covering (fig. 17). Experiments have 

 shown that hairy and spiny insects are distasteful 

 to birds and other creatures that prey readily on 

 smooth-skinned species, a conclusion that might well 

 have been expected. Certain smooth caterpillars 

 however appear to be protected by producing some 

 nauseous secretion, which renders them unpalatable. 

 Many of these, as the familiar cream yellow and 

 black larva of the Magpie Moth (Abraxas arossu- 

 lariata), are very conspicuously adorned, and furnish 

 examples of what is known as ' warning coloration,' 

 on the supposition that the gaudy aspect of such 

 insects serves as an advertisement that they are not 

 fit to eat, and that birds and other possible devourers 

 thus learn to leave them alone. On the other hand, 

 smooth caterpillars which are readily eaten by birds 

 are usually ' protectively' coloured, so as to resemble 

 their surroundings and remain hidden except to 

 careful seekers. Many such caterpillars are green, 

 the upper surface, which is naturally exposed to the 

 light, being darker than the lower which is in shadow. 

 When the caterpillar is large, the green area is often 

 broken up by pale lines, longitudinal as on the larvae 

 of many Owl Moths (Noctuidae) or oblique, as on the 

 great caterpillars of most Hawk Moths (Sphiugidae). 

 Such an arrangement tends to make the insect less 

 easily seen than were it to display a continuous 

 area of the same colour. The 'looper' caterpillars 



