CHAP. V.| COMMUNICATION AMONGST INSECTS. 49 



Hap oi the wing, thus at once making the noise and exposing the 

 flocculent yellow androconial hairs which line the interior ol the 

 pocket and which doubtless emit a smell attractive to the female. 

 It will he seen from figure 26 that the neurationa! structure of the 

 uini; is extraordinarily distorted, hut in the female, in which sex 

 the glandular pocket is absent, the neuration (system of wing-veins) 

 is normal. 



In the foregoing case the female maj he attracted to the male 

 by SOUnd or by smell and this instance therefore leads us to cases 

 in which oni 1 attracted by scents emitted by the other. 



Numerous instances of this attraction might be quoted especially 

 in the case of moths in which the males may he attracted from dis- 

 tances of several miles in search of a female; in such cases the 

 female is usually sluggish (often wingless (and the males have highly 

 pectinated (comb-like) antennae by which they perceive- the scenl 

 emitted by the female; this principle is taken advantage of by 

 entomologists who expose a virgin female in a small cage and 

 capture the males as thej "assemble." In manj butterflies, 

 especially the Pierids (" Whites ") and their allies, the males have 

 on their wings specially modified scales, called " androconia, " from 

 which they emit a pleasant perfume which is quite perceptible in 

 living or fresh specimens and which is undoubtedly attractive to 

 the female. 



Attraction of the sexes bj sight is very commonly met with and 

 has produced the evolution of many of the strikingly handsome 

 colours exhibited by the males of sexually-dimorphic insects, 

 spiders, lizards, birds, etc., already rendered familiar in innumer- 

 able publications. A very striking case amongst insects is. 

 however, afforded by certain glow-worms in which the wingless 

 female alone is luminous and gives out a beam of light by which 

 the non-luminous wingeilm.de is attracted to her. whereupon the 

 light is obscured. 



As may be expected, it is amongst social insects that we find 

 that means of communication have attained their maximum effici- 

 ency and in such cases tin- methods empl perhaps n 

 truly communicative than merely sexuallj attractive as in tin- 

 foregoing instances. There are lew t fill \ social beetles but the 

 Passalids may fairly be included in this category. These arc- lai 

 black beetles found commonly in the hills in rotting wood in which 

 they occur in small family parties usually consisting of immature 

 and adult forms ; the larvae have the first pair of legs modified into 

 stridulating organs and the beetles themselves also are able to 

 stridulate. When such a famil) part) is dislodged from a rotten 



