58 ACCOUNT OF THE GENERAL MEETINGS AND ANNUAL MEETING. 
she takes no food and drinks no water. Caterpillars consume 
vastly greater quantities of food in proportion to their size than 
other animals — in fact, as much as twice their own weight in 
leaves. This is as if one ox were to eat three-quarters of a ton of 
grass a day. Linnaeus stated that three flies would eat a dead 
horse as quickly as a lion. This is true if the progeny share in 
the feast. Hewitt estimates that the offspring of a pair of flies, if 
none are destroyed, would occupy a space of a quarter of a million 
cubic feet in four months. The Lecturer pointed out the inter- 
dependence of birds and insects, and how impossible it would be 
for the former to exist in such vast numbers if it were not that 
the latter were so enormously prolific. Migration and hiberna- 
tion are largely questions of food supply. Birds often travel long 
distances in search of food. Any day in Bristol rooks may be 
seen leaving their sleeping quarters in Ashton Park early in the 
morning and flying to Horfield and Almondsbury, whence they 
return in the evening. There are about 50 species of common 
British birds. Some are very prolific, and have three or four 
families during the breeding season. The number of insects 
required as food for the young is enormous. Professor 
Macgillivray noticed a thrush make 216 visits to the nest with 
food from 2.30 a.m. to 7 p.m., and a blue tit has been seen to 
make 475 journeys during a working day of 16 hours. 
" Dr. A. E. Shipley, at a meeting of the British Association in 
1 909, estimated the number of species of animals then known at 
790,533. Of these 13,800 are birds and 445,978 insects. 
It is birds which mainly keep down this vast insect life. 
From Professor Gathe's observations in Heligoland we can realise 
what large numbers of migrants reach their feeding and breeding 
grounds just as insect life is waking up and plants are beginning 
to bloom, and the constant interaction which is going on between 
various forms of life. The Lecturer then gave an account of some 
of the means adopted by animals to secure their prey. Some 
hunt and stalk, others conceal themselves and leading a 
stationary life resort to lures and various devices, as the angler 
fish. Some again, as parasites, depend entirely on others, while 
some are commensals and live as fellow boarders. As one instance 
of the latter, the hermit crab and sea anemone were given. The 
latter lives on the shell which forms the crab's house, and is thus 
carried about to fresh pasture grounds. The commensal ism of 
the hermit crab and a worm, which lives in the brightest chamber 
of the whelk shell and slips down and helps itself when the crab 
is feeding, was also mentioned. Of all animals insects may be 
regarded as the most completely equipped for getting food from 
various sources, as they are able to extract it from such different 
things as succulent fruit and the leg of a chair or the case of a 
grandfather's clock. According to Kirby 30 different species 
feed on the nettle alone, and as many as 200 on the oak. The 
Lecturer concluded by saying he had only touched on the fringe 
