74 BRITISH INSECTS 



burrow outwards, and in this way curious and char- 

 acteristic patterns are traced upon the surface of the 

 wood. Each grub pupates at the end of its burrow, 

 and the perfect insect eventually bores a hole through 

 the bark in order to effect its escape. One of the 

 commonest species is the elm-bark-beetle. 1 Another 

 is the pine-bark-beetle, 2 which does much damage in 

 its perfect state by burrowing into the young shoots of 

 the Scots pine in order to feed, be it noted, since the 

 eggs are laid beneath the bark in the manner described 

 above. 



The series Polymorpha now claims our attention. 

 We have already seen that it can only be characterized 

 by the fact that its members do not belong to any of 

 the other five series. Only the more interesting and 

 important families can be mentioned here. 



The whirligig - beetles 3 are by some authors in- 

 cluded with the Adephaga, but they differ greatly in 

 structure, notably in having each compound eye divided 

 into two. One isolated half of each eye is directed 

 downwards, thus enabling the insect to search for its 

 aquatic prey ; the other half keeps watch above ; for 

 whirligig-beetles seldom enter the water, except to 

 escape danger, but spend their days skimming rapidly 

 over the surface. The larvae, however, are completely 

 aquatic, and breathe by means of abdominal gill- 

 filaments, not unlike those of an alder-fly larva. 

 When full grown, they leave the water and spin small 

 papery cocoons upon the leaves and stems of plants. 



Members of the family Hydrophilida may be recog- 

 nized by their long maxillary palpi. Some of the 

 species are completely aquatic, while others frequent 

 marshy spots. The majority are quite small, but 



1 Scolytus destructor. 2 Hylurgus piniptrda. 3 Gyrinida. 



