230 DIVERSIONS OF A NATURALIST 



injured insects, which they snapped up in eager rivalry 

 as the infatuated flame-seekers dropped, hour after hour, 

 to the floor. The instinct, the nervous mechanism, which 

 brought the greedy reptiles to the spot was a " harmony," 

 a valuable guide to nutrition ; whilst the flame-seeker's 

 impulse is assuredly a " disharmony " a defect in ad- 

 justment leading -to death. 



It is interesting to inquire into the probable origin 

 of this fatal desire for close contact with a source of 

 light, a desire so strong as to be entirely unchecked by 

 the deadly heat accompanying the light. The May- 

 flies or Ephemerids are delicate little creatures, having 

 four net-veined wings rarely more than three-quarters of 

 an inch across, with two or three long filaments hanging 

 from the tail. Three hundred species are known from 

 all parts of the world, of which forty occur in the 

 British Islands. They live as wingless, six-legged larvae 

 in the water for a couple of years, feeding voraciously. 

 Then one summer's evening they very rapidly escape 

 from their larval skin and fly over the water in countless 

 swarms. But only for a few hours. The eggs of the 

 females are fertilized, and they all, both males and 

 females, drop dead or dying into the water, where they 

 are greedily devoured by fishes. The males are far 

 more numerous than the females; in some species as 

 many as 6000 males to one female have been counted, 

 They are attracted to an extraordinary degree by 

 lights (flames or electric lamps) set up for nocturnal 

 illumination by civilized man, and in some districts they 

 are collected by fishermen in this way for use as food 

 for fish, or were so in Holland in the eighteenth century 

 according to Swammerdam's statement in his " Biblia 

 Naturae." Why do they thus seek artificial lights ? There 

 is some indication of an explanation in the fact that two 



