324 Insects and their Surroundings 



cannot of course be regarded as mimicry, and may 

 fairly be set down as "accidental." Where, as is 

 almost always the case, the mimic occupies the same 

 area as the species which it resembles, the theory of 

 " similar conditions " is invoked to account for the like- 

 ness. But if this were the only cause, cases of mimicry 

 should be very numerous, and should occur indefinitely 

 among the various families and orders. Wasps and 

 bees should be modified to look like moths, and at 

 least some danaine butterflies should forsake the colora- 

 tion usual in their family to assume the comparatively 

 sober hues of nymphalines. Such cases are however 

 quite unknown, and the fact that only those species and 

 groups are mimicked, which are believed on good 

 grounds to be protected, goes far to show that there 

 is some advantage in mimicry to those insects which 

 have adopted it. 



Sexual Modifications. — Reference has already 

 been made to various points of form and colour in 

 which some male insects differ from their females. 

 In almost all cases where an outward divergence 

 between the sexes is to be observed, the male, though 

 smaller, is more highly developed than the female. 

 His sense organs are often more complex. Many male 

 Moths and Beetles are provided with saw-like or comb- 

 like feelers, while those of their females are simple. 

 The eyes of many male Flies and Bees occupy a larger 

 part of the head-area than do those of the females. The 

 males of Cicads and many Locusts and Grasshoppers 

 have highly developed sound-producing organs, which 

 are absent or rudimentary in their mates. The tail 

 forceps of male Earwigs aire longer and more complex 

 than those of the females, and a corresponding differ- 

 ence between the mandibles of the two sexes is to be 

 seen in many Beetles and in some Lacewing-flies and 

 Wasps. Spiny processes, sometimes of much com- 



