BIONOMICS. 325 



cases of pebbles and fragments of stem ; many caterpillars 

 and adult insects harmonise with the colour of their environ- 

 ment ; leaf insects, " walking sticks," moss insects, scale 

 insects, have a precise resemblance to external objects which 

 must often save them ; a humming bird moth closely resem- 

 bles a humming bird ; many palatable insects and larvae 

 have a mimetic resemblance to others which are nauseous or 

 otherwise little likely to be meddled with. Many insects 

 may be saved by their hard chitinous armour, by their dis- 

 gusting odour or taste, by their deterrent discharges of 

 repulsive formic acid, &c., by simulation of death, by active 

 resistance with effective weapons. 



Many flowers depend for cross fertilisation upon insects 

 which carry the pollen from one to another. Many insects 

 depend for food on the nectar and pollen of flowers. Thus 

 many flowers and insects are mutually dependent. But 

 many insects injure plants, and many plants exhibit structures 

 which tend to save them from attack. On the other hand, 

 there may be " partnerships " between insects and plants 

 witness the " myrmecophilous " (ant loving) plants which 

 shelter a bodyguard of ants, by whom they are saved from 

 unwelcome visitors. And again, the formation of galls by 

 some insects which lay their eggs in plants, and the insect 

 catching proclivities of some carnivorous plants, should be 

 remembered. 



Most insects are terrestrial and aerial; the majority live in 

 warm and temperate countries, but they are represented 

 almost everywhere, even above the snow line, in arctic 

 regions, in caves. Even on the sea the " Challenger " ex- 

 plorers found the pelagic Halobates, a genus of bugs. The 

 distribution of Insects is mainly limited by food supplies 

 and climate, for their powers of flight are often great, and 

 their opportunities of passive dispersal by the wind, floating 

 logs, &c., are by no means slight. 



Many insects are more or less parasitic, either externally 

 as adults, e.g., fleas, lice, bird lice, plant lice, &c., or inter- 

 nally as larvae, e.g., the maggots of gad flies on cattle, and a 

 great number of borers within plants. 



We need only mention Hessian fly, Phylloxera, Colorado 

 beetle, Weevils, Locusts, to suggest many more which are of 

 much economic importance as injurious insects. On the 



