120 



THE GAKDENER'S ASSISTANT. 



are of various sizes according to the species, 

 but generally have dark-brown or black bodies, 

 variously ornamented with curved yellow spots 

 almost meeting upon the back of the abdomen, 

 or the yellow bands may be continuous, giving 

 the flies the appearance of small wasps, though 

 some of the species are as large as the drone 

 amongst hive -bees, for which they might be 

 mistaken, except by their manner of flight, and 

 by having two instead of four wings. The 

 eggs are laid upon plants amongst colonies of 

 aphides, and the maggots, when hatched, com- 

 mence feeding upon the helpless aphides, which 

 they seize in their mouth and suck the contents, 

 rejecting only the empty skin. A hungry 

 maggot can thus destroy one hundred aphides 

 in an hour. The maggots may be recognized 

 by their relatively large fleshy and thin-skinned 

 bodies at rest amongst the aphides, or sluggishly 

 crawling about. They are whitish, pale-green, 

 or yellow, and in some cases lined or variegated 

 with orange. When full-fed they fix themselves 

 to a leaf, stem, or other object by the tail, 

 assuming a pear-shaped form while the skin 

 hardens. This is the pupa stage, and the perfect 

 flies emerge in a few days to resume the work 

 of their parents. Neither form should be de- 

 stroyed if it can be helped, for these hawkflies 

 serve largely to keep the myriads of aphides. 

 Including American Blight, in check. 



Hornets (Vespa crdbro). — It is doubtful 

 whether gardeners would care to encourage the 

 increase of this venomous, stinging insect; but 

 it may be some consolation to know, and a plea 

 in their favour, that they live almost entirely 

 upon other insects, including wasps. The hornet 

 is really a large species of wasp, and is most 

 often met with in the south of England, where 

 it makes its nest in outhouses and the hollows 

 of trees. 



Ichneumon Flies. — These are legion, and 

 found everywhere over the British Isles. They 

 belong to the same great order as ants, wasps, 

 and bees, and constitute a family of parasites 

 whose function in the economy of nature is to 

 maintain a balance amongst the various insect 

 tribes, while they themselves are often preyed 

 upon by smaller species of the same family. 

 From their habits they are apt to be mistaken 

 for the cause of the disease, due to the attacks 

 of the insects whose larva? they prey upon. 

 They have four wings, and the abdomen is often 

 almost separated from the rest of the body by 

 a narrow joint or stalk. In form and colour 

 they vary immensely. Some lay their eggs in 

 caterpillars or the pupae, and the maggots feed 



upon the soft but less vital parts of the ho^t 

 until the caterpillar or pupa is about to pass 

 into another stage, when it dies, unable to effect 

 the change. An example of this is shown in 

 Fig. 155, the living caterpillar on the left 

 being covered with a swarm of ichneumon 

 maggots, which destroy it, and its dead body 

 becomes a bed for them in the cocoon stage. 

 Sometimes two to four small brown or black 



Fig. 155.— Caterpillar devoured by the Larva? of Ichueunious, and 

 Caterpillar covered with their Cocoons. 



cases, that is, pupae of some or other of these 

 parasites, will come out of a caterpillar in which 

 the maggots have fed; but in the case of the 

 Large White Cabbage Butterfly, its parasite 

 (Microgaster glomeratus) will lay from thirty to 

 sixty or more eggs in the caterpillar. When 

 about full-grown, the latter sickens and refuses to 

 feed, when the maggots gnaw their way out and 

 form clusters upon Cabbage-leaves, where each 

 spins a yellow silken cocoon, generally beside 

 the empty skin of the caterpillar or upon its sur- 

 face. The caterpillar of the Death's-head Moth 

 does not escape, but is attacked by the largest of 

 the British ichneumons, which lays her egg in 

 the body of the larva, where the maggot hatches, 

 grows to a large size, and finally emerges instead 

 of the moth. Other parasites of this family lay an 

 egg in each aphis they may select, and in which 

 the grub feeds. Aphides attacked in this way 

 become swollen, fixed to the leaves on which they 

 have been feeding, and later on they die in the 

 same position, becoming pale-brown. Thus al- 

 | most every species of caterpillar, grub, maggot, 



