88 ECOLOGY AND LIFE HISTORY OF THE COMMON FROG 



none to hatch into tadpoles, so that this is another case of catastrophic 

 control of numbers. 



The snake, Matrix natrix, is, however, perhaps in a different category. 

 It is not a very large animal, one frog forming a meal that may last for 

 days, it hibernates in the winter, and it lives in similar places to the 

 frog. It is possible to conceive that the numbers of snakes varies with 

 the numbers of frogs in one of the ways suggested by those who have 

 studied these reciprocal relations. I have no close knowledge of 

 the density of the population of frogs in Ireland, where there are no 

 snakes, but in the south-west I saw more than I have seen anywhere 

 else except in the Alps, and a correspondent, Mr. C. Paris, reported 

 so many that I scarcely recognized his picture of numbers in comparison 

 with mine. It is possible that a controlling factor is absent from 

 Ireland, so that the normal level of population is higher than in 

 England. But perhaps climate is at the bottom of the matter. 



Disease 



As in most other wild animals, records of disease in frogs are almost 

 absent. I once found a spent female frog dead beside a spawn pond. 

 Her lungs were so full of nematodes that I concluded that they could 

 not be functional. She probably died when, her water-hfe over, she 

 attempted to resume her role as a land animal, dependent on aerial 

 respiration. 



Man as a Predator 



In spite of the fact that, when we deal with our own species, we 

 should be well informed, there is much doubt about the part man 

 plays as a predator. Fischer-Sigwart (1897) working near Zurich in 

 Switzerland has a detailed account of the effect of catching frogs for 

 food. He describes how the frog-catchers took 1,500 pairs a night 

 from the ponds he was studying. Taking advantage of the high degree 

 of local autonomy in Switzerland, Fischer-Sigwart persuaded the 

 Commune to ban the taking of frogs. The frog-catchers evaded the 

 law by coming stealthily by night, but eventually, Fischer-Sigwart 

 found ponds out of their reach, and was able to continue his studies. 

 This is a very detailed account, and with this large drain on the local 

 suppHes of frogs, there must have been a danger of extinction. But 

 Fischer-Sigwart says that the decline began before the frog-catchers 

 arrived, and the numbers taken were so large that, even then, there 



