CHAP. IV.] 



MEANS OF DEFENCE IN INSECTS. 



4? 



Some insects secure themselves from attack by constructing 

 shelters or little houses which they drag about with them, this being 

 probably a highly developed form of a primitive concealed mode 

 of living for defensive purposes. The Rice Case-worm (Nymphula 

 depunctalis) and the common Bagworm (Clania crameri) are familiar 

 instances. The larvae of many of the Cassid beetles are provided 



ul larva f Aspidomorpha sanctce-crucis), commonly 

 found on Sweet-potato, carrying its excrement over its back. 

 Three times the natural si/c. (( Iriginal.) 



with a long forked "tail " which they hold over the back and carry 

 on it their cast skins and excrement, so that the true nature of the 

 larva is often concealed. Several predaceous larva; (Chrysopa, 

 Eublemma, etc.) place the empty skins of their victims on their backs 

 and thus achieve concealment at once from enemies and prej . For 

 it must be remembered that a structure, marking, etc., may plaj 

 more than one pari in the economy of an animal, whether insect or 

 not, and that a predaceous animal which is protected from its 

 enemies by its procryptic coloration is equally equipped for 

 approaching its prey. Colours which are bright and "warning" 

 to foes may be alluring to prey and also attractive to the opposite 

 sex. 



Luminosity in insects may be briefly considered here as it is at 

 times a means of defence although probably more often of use for 

 sexual attraction. The best known examples of luminous insects 

 in India are the numerous species of glow-worms, usually errone- 

 ously called " Fireflies " although the true Fireflies, belonging to the 

 family Elateridce, do not occur in India. In glow-worms the lumi- 

 nous organs are usually placed beneath the posterior segments of 

 the body. In many species only the male is winged, the female 

 being wingless and grub-like, both this sex and the larva having 

 luminous organs. The luminosity is entirely voluntary and is often 

 rhythmic, large numbers of individuals emitting a momentary flash 

 with one accord. The efficiency of the light emitted by these little 



