134 PROTECTION OF WOODLANDS. 



In the few species whose ova are deposited in clusters, the 

 larvse form family galleries or galleries in common, whilst (accord- 

 ing to Eichhoff, an authority on the Scotytidx) in the case of the 

 timber-borers true larval galleries are nob formed, as the larvae 

 live in the main galleries, and only hollow out short cone-like 

 galleries, at right angles to the main gallery, for their pupal 

 chambers, the whole being specifically known as ladder galleries. 



The main galleries, and the larval galleries connected with them, 

 usually form very characteristic designs that in most cases very 

 materially simplify the recognition of the species of insect to 

 which the damage is due ; whereas the determination of the species 

 by a mere examination of the larvae only would not be possible. 



The period elapsing between the deposition of the ova and the 

 development of the mature imago, varies not only according to 

 the species, but also according to the general kind of weather, 

 and in particular according to the temperature of the breeding- 

 place. Thus the period of generation is of longer duration in the 

 hills and mountains than on the warmer plains ; but on the average 

 it lasts only from 8 to 10 weeks. The chrysalides lying in the 

 pupal chamber already exhibit all the different sections of the 

 perfect beetle, from which they are mainly distinguished by their 

 lighter colour and their softness of structure. After a pupal rest 

 of about 8 days they undergo the metamorphosis into the fully 

 developed beetle, but usually, especially when the weather is raw 

 and cold, spend a few days feeding on the succulent cambial layer 

 surrounding the pupal chamber, which then rather interferes with 

 the characteristic appearance of the larval galleries. When, how- 

 ever, the weather is fine, the beetle bores a small circular exit-hole in 

 the bark, and generally at once begins to swarm and to reproduce 

 itself in a new brood. This attains its complete development in 

 the same season, but as a rule does not swarm until the following 

 year ; the beetles hibernate in the meantime under the bark, in 

 fissures and cracks, in roots, stumps of trees, &c. Most bark-beetles 

 have such a double generation, although, in regard to a few species, 

 this has not yet been proved beyond doubt ; but local circum- 

 stances have always more or less of influence in this respect, for 

 one and the same species may have a double generation in warm 

 localities, whilst only having a single or annual generation in less 

 favourable situations. 



The presence of bark-beetles in stems lying on the ground 



