as Enemies of Mankind. 



9 



partitions and ceilings. Again, attracted by the food of the pit 

 ponies, as well as by the drainage, rats find coal mines quite 

 comfortable places to live in ; and they often find their way from 

 one mine to another. 



Whenever necessary this species digs with great facihty. Out- 

 of-doors its burrows consist normally of winding galleries, drilled 

 in banks or hedgerows, and furnished with several bolt-holes. The 

 burrows are frequently established in soft and warm materials, 

 such as manure heaps and rubbish mounds ; wheat stacks, hay 

 ricks, and thatch also offer special attractions and are often riddled 

 with rat holes. It shows a good deal of inquisitiveness, and will 

 dig out bulbs and roots from garden beds, sometimes, apparently, 

 merely to satisfy its curiosity. Furthermore, every passing rat 

 will be attracted by the spoor of its predecessor, so that if one 

 marauder be caught another soon takes its place. 



This species carries out a partial migration at different seasons. 

 In spring many individuals from farm buildings and towns betake 

 themselves to the open fields, where they establish burrows and 

 pass the summer. As autumn advances many forsake the fields 

 and re-enter buildings for the winter. It is said that in years 

 with a plentiful acorn crop fewer return to houses and more 

 remain to pass the winter in the open. The breeding rate, how- 

 ever, depends upon the amount of food available and upon the 

 competition for it ; the rat population in the buildings is quickly 

 compensated for the extra number left behind in the fields, and in 

 the following spring the numbers migrating for the open are not 

 sensibly diminished. During the ensuing summer the outdoor rat 

 population rises much above the normal. Similar movements are 

 connected with periodical changes in food-supply ; thus, it is said 

 that large numbers* of rats visit our coast during the herring 

 fishery, and that they pass inland again in October after this 

 fishery has stopped. In all these movements waterways of all 

 kinds, as already mentioned, play a large part. Mr. E. E. Parker 

 of Norwich, in litt. to Dr. Harmer, says : " Lynn ... is infested 

 w^ith rats which annually migrate over W. Norfolk — they are 

 destroyed in hundreds at Sandringham. We find always that 

 rats in a dry time in spring return to the rivers and in autumn 

 they come back up the rivers. You may have a farm clear of 

 rats one week and well stocked the next." 



Although rats attack and devour such of their fellows as are 

 injured and too weak to defend themselves, they are normally 



B 2 



