LEAF-ROLLING APHIDES. 343 



stalk. The latter sort of galls are of a spiral form ; and 

 though they are closed, they open upon slight pressure, and 

 appear to be formed of two lamina3, twisted so as to unite. 

 It is at this opening that an aperture is formed spon- 

 taneously for. the exit of the insects, when arrived at a 

 perfect state. In galls of this kind we find aphides, but of 

 a different species from the lanigerous ones, which form the 

 horn-shaped galls above described. 



■ Leaf-Rolling Aphides. 



It may not be improper to introduce here a brief sketch 

 of some other effects, of a somewhat similar kind, produced 

 on leaves by other species of the same family (Aphidce). In 

 all the instances of this kind which we have examined, the 

 form which the leaf takes serves as a protection to the 

 insects, both from the weather and from depredators. That 

 there is design in it appears from the circumstance of the 

 aphides crowding into the embowering vault which, they 

 have formed ; and we are not quite certain whether they 

 do not puncture certain parts of the leaf for the very pur- 

 pose of making it arch over them ; at least, in many cases, 

 such as that of the hop-fly (^Aphis liumuli), though the insects 

 are in countless numbers, no arching of the leaves follows. 

 The rose-plant louse, again (Aphis roses), sometimes arches 

 the leaves, but more frequently gets under the protecting 

 folds of the half-expanded leaf-buds. (J. E.) 



One of the most common instances of what we mean 

 occurs on the leaves of the currant-bush, which may often 

 be observed raised up into irregular bulgings, of a reddish- 

 brown colour. On examining the under side of such a leaf 

 there will be seen a crowd of small insects, some with and 

 some without wings, which are the Aphides ribis in their 

 diiferent stages, feeding securely and socially on the juices 

 of the leaf. 



The most remarkable instance of this, however, which 

 we have seen, occurs on the leaves of the elm, and is caused 

 by the Aphis idmi. The edge of an elm-leaf inhabited by 

 those aphides is rolled up in an elegant convoluted form, 



