LARCH-BUG AND WOOD-WASPS. 79 



live in numbers, either entering the chambers during the growth of 

 the gall, or being enclosed by the swelling of the surrounding 

 needles. 



The galls sometimes completely surround the base of the shoot, 

 sometimes they are only developed on one side. The larvae are 

 closely packed in the chambers, from twenty to fifty being found in 

 each one. When they are fully grown in August they acquire wings 

 and leave the chambers by apertures left by the shrinking apart of 

 the leaves. These insects are winged females, and their special 

 function is that of spreading the species on to other trees. The 

 effect of the galls on the tree is to cause crippling of the attacked 

 shoot, and when they are abundant the general growth of the tree is 

 much impaired. 



Larch-bug. The females of Chermes laricis, which also pass 

 the winter under bark, etc., appear in the spring like those of 

 C. abietis ; they also are wingless, oval, of small shape, and of a 

 purplish black colour, and have a long bristle-like sucker with which 

 they penetrate the needles to feed on their sap. Towards the end of 

 April they lay forty to fifty eggs on the twigs. The young produced 

 scatter themselves over the needles, and do not live enclosed in a 

 gall ; at first very minute and blackish, they grow rapidly and become 

 covered with a whitish woolly down exuding from pores on their 

 body, giving the trees the appearance of being covered with minute 

 scattered, snow-crystals. About June they acquire wings and spread 

 the species, while further broods are produced till the autumn. This 

 insect occurs on Larches of all ages, being found, perhaps, most 

 frequently on trees of ten to twenty years old ; it not infrequently affects 

 young Larches in nurseries, and may there be very troublesome. 



Wood-wasps. There are many insects which take possession of 

 the dead or dying tree to lay their eggs therein wjiose larvae 

 burrow into and penetrate the wood, making it useless for commer- 

 cial purposes. Of these the most important are the wood- wasps, 

 Sir ex gigas and juvencus, large Hymenoptera of elongate shape. S. 

 <jigas is yellow T -and- black, and of a decided wasp-like appearance, while 

 S. juvencus is deep blue, with the middle segments of the abdomen 

 reddish in the male. 



These insects appear to be somewhat widely distributed in Great 

 Britain and Ireland, and are occasionally not rare. Owing to their striking- 

 appearance and loud buzz in flight, they attract general attention, and 

 are probably as rarely overlooked as any indigenous insects. Not a few 

 recorded specimens are obviously imported in foreign timber. The 

 females of both species lay their eggs exclusively on Conifer-wood, 

 choosing, as is so often the case, sickly or dying trees, or those that are 

 actually felled or dead. Sirex gigas appears to attack principally the 

 Spruce and Silver Fir, sometimes the Larch and non-European 

 Conifers like the Deodar. 



Sirex juvemus, on the other hand, attacks the Scots Pine freely, as 

 well as the Spruce, Silver Fir, and Larch. The eggs are deposited 

 in cracks running through the bark into the sapwood, or in holes 

 made by the strong ovipositor, and not rarely on patches of bare wood 

 where the bark has been torn off by accident. This sometimes gives 

 an opportunity for injury to otherwise healthy trees. The larva, whose 

 life extends over two years, is a stout, elongate white grub, readily 



