224 SOME ASPECTS OF ECOLOGY 



to that of food (Table VI.). Grain weevils have a water content of 

 45 to 50 per cent. ; in the cabbage butterfly larvae it is 83 to 84 

 per cent. Payne also found that cold resistance is greater in 

 starved larvae and lower in those fed with moist food. Her 

 conclusions have been confirmed, and in some directions amplified, 

 by the work of Sacharov (1930). This experimenter paid 

 particular care to the technique employed. He avoided the 

 insertion of thermopile needles into the insects by employing the 

 dilatometer and criohydrate solutions. In this way surgical 

 shock, which causes a measurable rise in temperature, was avoided. 

 Sacharov's conclusions are apparently based upon careful technique, 

 and they may be briefly summarised as follows. Cold hardiness 

 depends upon two intrinsic factors : (1) the proportion of easily 

 freezable water to the total water content, and (2) the percentage 

 of fat present. Hibernating insects, he claims, fortify themselves 

 by reducing the one and increasing the other. He tested these 

 two factors in the caterpillars of the brown-tail moth taken 

 straight from hibernation and after feeding for several days in a 

 warm chamber. The differences are very striking, and his results 

 are quoted below (Table VIII.). 



Sacharov further carried out a number of observations upon 

 different insects, taken from their natural habitats during winter, 

 and subjecting them to different temperatures. His results are 

 shown in abstract in the accompanying table (Table IX). With 

 chafer larvae he points out that the reason for their penetration to 

 greater depths in the soil during hibernation appears to be due to 

 their possessing but a limited capacity for cold hardening. They 

 would seem to have an exceptionally high w^ater content and even 

 at a temperature no lower than — 5-7° the amount of non-frozen 

 water w^as found to be only 25-7 per cent, of the total water. The 

 hive bee is well known to be susceptible to the effects of cold and 

 damp and requires well-insulated quarters for hibernation. In 

 this connection Sacharov's results are rather unexpected, since it 

 would seem that this insect is more resistant than chafer larvae. 

 The adult of the herald moth (Scoliojpteryx lihatrix) and the larvae 

 of the longicorn (Plagionotus arcuatus), are both highly resistant 

 to the cold. In the case of the herald moth, which hibernates 



