XIX INSECTA : RHYNCOTA 287 



which seems to be the grub of a parasite (one of the Braconid 

 Ichneumon-flies called Praon) that has lived within the 

 body of the Aphis for a time, and then eaten its way out, 

 killing the Aphis, and protecting itself by the silk-woven disc. 

 Among the other enemies of Aphides are the Ladybird 

 (p. 251), the Hover Fly grub (p. 332), and the larva of the 

 Lacewing Fly (p. 316), each of which accounts for a prodigious 

 number of Green-fly. The Blue-tit also is a good friend to 

 the gardener in this respect. 



There are many dififei'ent kinds of Aphides 



Anhis' ^ inhabiting different plants. The Bean Aphis, Plum 

 Aphis, Pea Aphis are all very destructive, also the 

 " Woolly " Aphis, which lives on the branches and on the 

 roots of apple and pear trees, forming round themselves masses 

 of a white woolly substance excreted by certain glands in their 

 backs. The flies themselves are a purplish-brown colour, 

 except for the wingless egg-laying females, which are reddish- 

 yellow and very small, not usually more than -j-jnnr °f ^^ ™'^^ 

 long. These curious females and wingless males are to be found 

 in the autumn. One egg is laid and then the female dies. This 

 sexual reproduction only takes place rarely. During those 

 years that it is absent, the race is carried on from year to year 

 by the hibernating parthenogenetic females. The Woolly 

 Aphis has no secreting tubes projecting from the abdomen. 



The various common Aphides do not cause any gall to form 

 on the plants on which they feed, but the closely allied genus 

 Chermes causes the production of the well-known " False Cone 

 Galls " on the spruce fir (Fig. 214). 



Chermes (Bark-lice). 



The life-history of this form is extraordinarily complex, and 

 it is given here as an example of the curious phenomenon of 

 the same insect passing different definite stages of its life on 

 different plants in a regular cycle of generations. It will 

 be perhaps simplest to start at the stage in which the 

 Chermes insect passes the winter on the spruce fir — the stage 

 known as Chermes abieiis. 



Generation ^^ spruce twigs are examined in November, 

 I. On there may be seen on some of the terminal clusters 

 Spruce. q( ijuds^ especially in the crevices between the buds. 



