68 



their smallness have so far baffled all efforts to counteract them, and the Chalcididse have 

 received a high place in the estimation of all from the discovery that they prey upon some 

 of those species which have appeared in such numbers as sometimes to threaten the total 

 destruction of certain crops throughout whole districts, as for instance the various species 

 of Cecidomya, a genus which includes many of the most dreaded pests as the Hessian fly, 

 the wheat midge, the clover leaf and clover seed midges, and also many gall-forming species. 



And now we come to some injurious kinds of Hymenoptera — first of all the gall flies 

 which are closely allied to the chalcids ; but are plant parasites. When the egg is laid in 

 the leaf or green bark of a plant an abnormal growth of the vegetable cells is brought 

 about which forms large tumors; upon the substance of these the larvae feed. "These insects 

 are examples of the uses that lie hidden in nature. Many thousand years had the gall 

 flies been making their wonderful cells before any one discovered that the galls which 

 disfigured the oak could be of any service to man. Yet within the gall lay the principal 

 element of the ink which has had as important a part to play in civilization as the 

 press itself, the latter depending almost wholly on the former. Scarcely larger than 

 average sized hazel-nuts, the galls absolutely crowd the branches of an oak which grows 

 plentifully in the Levant, and so it is to these insignificant insects that we owe one of the 

 most absolute necessities of modern existence."* 



The saw-flies seem to be a sort of intermediate link between the Hymenoptera and 

 Lepidoptera ; while the perfect flies are certainly Hymenopterous the larvae closely re- 

 semble the caterpillars of Lepidoptera, they may, 

 howe ver, be easily known by the number of their 

 legs which is twenty two, while true caterpillars 

 have only sixteen, and also by a habit of curling up the 

 hind part of the body when at rest ; when full 

 grown they spin a hard silken coccoon. The saw, 

 or ovipositor, is a beautiful and complicated appar- 

 atus ; with it the female makes incisions in different 

 parts of leaves and deposits an egg in each slit. 

 Some, however, as the common gooseberry fly (JVem- 

 atus ventricosus) lay their eggs on the under side of 

 the leaf (as shown in fig. 54), not inserted in the 

 substance of it at all. 



These insects are exceedingly troublesome, and 

 have to be constantly watched and treated to " helle- 

 bore " or they will entirely denude the gooseberry 

 and currant bushes just at the time the fruit is 

 forming, when the leaves are most wanted. I am 

 happy to say, however, that I have noticed this year considerable ravages among these larvae 

 and those of the common white butterfly, made by some fungous disease. 



Another too well known saw-fly larva is the pear-tree slug (Selandria cerasi), which is 

 sometimes very destructive. 



There is also belonging to this sub-order a clumsy bow-legged purple and yellow fly, 

 with clubbed anteunse called Gimbex Americana, the large handsome larva of which 

 may frequently be found feeding on birch and elm trees ; it is white, with a delicate green- 

 ish-yellow tint, and has a black line down its back and a spot of the same colour at each 

 spiracle. 



The last family is the Uroceridse or horn-tails, so called from a long horn upon the 

 abdomen of the males, the object of which is probably protective in adding to the already 

 formidable appearance of these insects. In colour and movements as well as somewhat in 

 form, they much resemble wasps. This family was fully described by Mr. Harrington in 

 the Canadian Entomologist for May of this year. 



J. Fletcher, Ottawa. 



* Wood's "Insects Abroad." 



