OV THE AVATEU-IJEKTLE rELOHIl'S TARDUS. 83 



between its jaws. Also, in my tumblers, the beetles immediately 

 became very active when a piece of worm was quietly dropped in, 

 even when they could not see it, and they would at once begin to 

 hunt round until they found it. 



3 (b) Longevity of imago in artificial environvient. 



In some of my tumblers I kept pairs, in others single indi- 

 viduals, each tumbler being supplied with a small piece of 

 water-weed, usually Modea^ and also with a few pebbles to give 

 foothold. The water was changed dail}^ or on alternate days, 

 according to circumstances, and 1 had no difficulty in keeping 

 the beetles alive for months and even for more than a year in 

 this way. Deaths that occurred were almost always among the 

 pairs, and the male succumbed more frequently than the female. 

 Presumably the cause of death in these cases was overcrowding, 

 six or seven ounces of water, even when changed daily, not being 

 sufficient for two individuals. 



I had previously experienced this difficulty in keeping several 

 individuals of a species in a confined space. For instance, 

 Hydrohius fascipes L., a smaller beetle than PeloUus, lived much 

 lono-er when one was kept in each tumbler than when two or 

 three were so kept. Of twelve individuals of such a small species 

 as Bidessits miautissimus Germ, only six sui-vived after a month, 

 two after three months, and one shortly after that, the last 

 survivor living for many months. At the same time six indi- 

 viduals of this same species, each in a separate tumbler, survived 

 for periods varying from one to three years, the water in these 

 tumblers never being changed, only a little being added from 

 time to time to make up loss due to evaporation. 



I have mentioned that, in the case of Pelobius, when one pair 

 was confined in a tumbler the male usually died first, Avhich 

 suo-o-ests that the male is not so hardy as the female. Experiments 

 showed that the female lives longer than the male. As I was 

 unable to find the details of about a dozen experiments carried 

 out in 1913— before the work described in this paper was com- 

 menced—I set aside four tumblers in May 1920, each containing 

 much decaying leaf material rich in Ghironomus larvte and various 

 other forms of life. In each tumbler I placed one Pelohius, using 

 for the experiment two males and two females. A small piece 

 of Eloiea was placed in each tumbler to keep the water fresh, and 

 each tumbler was covered with a piece of glass to reduce evapo- 

 ration. Nothing was done to these tumblers until May 1921, 

 by which time, out of the six ounces of water originally placed 

 in each of them, only about three remained. The two females 

 were^ alive but both the males were dead. 



3 (c) Siridulation. 

 PeloUus used to be sold in St. Martin's Lane, London, under 

 the name of the " Squeak beetle," owing to its being able to 



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