DAMAGE CAUSED BY ANIMALS. 205 



The Hop-dog or Beech-moth is to be found now and again in 

 single examples on almost every kind of broad-leaved tree, but large 

 swarms of them occur only on the Beech. It principally attacks 

 the older classes of Beech crops, especially such as- grow on soil 

 that is somewhat inferior in quality, and it is usually only when 

 these have been defoliated that it migrates to the pole-forests and 

 the other crops of younger growth. It often occurs in enormous 

 numbers, and is undoubtedly, above all others, the insect that 

 threatens most damage to the Beech. 



But the injuries inflicted are essentially diminished by the fact 

 that the feeding of the caterpillars principally takes place during 

 the later half of the summer months, after the formation of the 

 young buds, for the flush of leaves during the following spring, has 

 already taken place ; for experience has shown that, although the 

 generation is simple and annual, any plague of these caterpillars 

 seldom lasts longer than two consecutive years, so that as a rule 

 the damage actually done is, for the most part, confined to temporary 

 loss of increment, and to a prejudicial influence, both quantitatively 

 and qualitatively, on the mast-producing capacity of the trees. 



The caterpillars have numerous enemies amongst insectivorous 

 birds, including crows, cuckoos, thrushes, finches, tomtits, &c., 

 whilst of predatory insects, Carabidaz and Ichneumonida? decimate 

 them ; but it is chiefly to diseases of fungoid origin that the sudden 

 disappearance of enormous swarms must be ascribed. At the 

 same time, they are extremely sensitive to sudden changes in the 

 weather, although during the winter months comparatively insen- 

 sitive to the effects of snow and cold. 



As an annihilative and exterminative remedy, experience has 

 shown that attempts to collect the chrysalides, or to collect or squash 

 the caterpillars when descending the trees for the purpose of 

 forming their cocoons on the ground, are, on the whole, of no great 

 practical use, or are, at any rate, not effective in the degree desired. 

 As the eggs are deposited on the smooth bark of the Beech within 

 a moderate height (about 10 feet) above the ground, and are com- 

 paratively easy to find owing to their being laid in clusters, they 

 can be easily collected or destroyed, or can be effectively pre- 

 vented from hatching, or killed off if the larvae are collected in 

 schools by being smeared over with oil or patent tar, as this 

 brings death to both ova and larvae. But as the ova are deposited 

 within so short a distance of the ground, the simplest and most 



