THE BROWN OR COMMON RAT 625 
The rat flourishes on a shore diet. It thus manages to 
subsist on many of the smaller islands, as on Ailsa Craig, 
where it arrived in 1889, and eats the innumerable dead bodies 
of sea-birds falling to the bases of the cliffs.’ 
As a rule rats do not directly molest large animals, but 
they have been occasionally known to attack or kill men? or 
children,® and to gnaw the feet of elephants in the Zoological 
Gardens.* Their tendency to cannibalism is interesting in 
view of the fact that, as described above, they are at ordinary 
times friendly to all members of their species. Either they 
run amuck sometimes, or else they attack each other through 
some mistaken sense of injury.” Stories of rats eating each 
other when left over night in cages cannot be regarded as 
instances of their normal habits, since their sufferings from 
thirst and hunger probably madden them, and may lead them to 
connect their troubles with their comrades, as many ‘‘ game” 
animals do when wounded by a shot from an unseen hunter. 
Extraordinary calculations have been made as to the 
damage done by rats and the rate of their increase. F. von 
Fischer® calculated that a single pair might leave, after ten 
years, a progeny of 48,319,698,84 3,030, 344,720 rats. 
Mr Lantz’ calculates that in nine generations a single pair 
of rats would, if breeding uninterruptedly, produce more than 
twenty million individuals, but such a calculation is entirely 
theoretical. However, as he states that the average quantity 
of grain consumed by an adult or half-grown rat is fully 2 
ounces daily, or 45 to 50 lbs. a year, the average cost for 
feeding one rat for a year becomes about seven shillings and 
sixpence. If fed on meat, the cost would be higher, but the 
calculation is complicated by the fact that rats eat much waste 
products and, on the other hand, damage more than they eat. 
Many rats must each destroy fully five shillings’ worth of 
1 Boyd Watt, Ann. Scott. N.H., 1892, 132. 
2 In Walker Colliery, Killingworth, fide Robert Stephenson, M.P. (the distinguished 
engineer), quoted by Tomes in Bell, ed. 2, 311 ; see also Millais, ii., 229. 
3 Shipley, Journ. Econ. Biol., iii., 1908, 65. 
4 Frank Buckland, Curiosities Nat. Hist, 1.. 76; and Millais, ii., 229. 
6 Such highly “civilised” animals as dogs occasionally murder each other when 
confined together in numbers. 
8 Zool. Garten, 1872, 125. 7 Lantz, of. czt., 16. 
