PLANT-EATING INSECTS 193 



to the eye ; others feed over a wide area, and give rise to 

 unsightly, blister-like patches. The former method is 

 adopted by the caterpillar of a little moth which burrows 

 into bramble leaves, the latter by the maggot of a minute 

 two-winged fly which often disfigures the foliage of the 

 holly. 



A whole host of insects penetrate the soil and attack 

 the living roots of plants. Some of these, such as the 

 caterpillars of the swift moths and the grubs of chafer 

 beetles, do much damage ; while the so-called wireworms 

 are among the farmer's worst foes. Many other insects, 

 aided by powerful dissolvent ferments which they secrete, 

 subsist upon bark and wood. There is an old proverb 

 which avers that to go between the oak and the rind is a 

 practical impossibility; yet the grubs of many beetles 

 feed just beneath the bast, or inner bark, and immedi- 

 ately above the surface of the wood. The parent insect 

 makes a tunnel under the bark and deposits her eggs 

 alternately on either side, while the grubs, when they 

 hatch, burrow outwards to right and left, forming a 

 characteristic pattern. The full-fed grubs pupate at 

 the end of their burrows, and the perfect insects drill 

 holes through the bark in order to effect their escape. 

 These bark-boring beetles are thought to attack only 

 sickly or newly-dead trees, but the caterpillars of certain 

 moths burrow into the living wood. The case of the goat- 

 moth (Cossus ligniperda) may be cited. The female lays 

 her eggs in crevices of the bark, and the caterpillars pene- 

 trate the stem, in which they drive long tunnels. They 

 continue for three years before they assume the pupa 

 state, and in this period increase 72,000 times their 

 original weight. It is hardly necessary to add that the 

 goat -moth slowly destroys trees to which it gains access. 

 The majority of wood-feeding insects, however, confine 



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