170 * APHIS. 



cockle or warp in* such a manner as to form one 

 or more large concavities beneath, and in which 

 the insects generally reside in great multitudes. 

 In some years they are so numerous as to cause 

 almost a total failure of hop and potatoe planta- 

 tions : in other years the pease are equally injured, 

 while exotics raised in stoves and green-houses 

 are frequently destroyed by their depredations. 

 They are also supposed to be the chief, if not the 

 sole cause of that viscid exsudation or moisture so 

 often observed on the leaves of various trees, and 

 popularly known by the title of honey-dew ; which 

 is said to be nothing more than the excrementiti- 

 ous substance evacuated by these insects from the 

 hinder part of the body and from the two tubular 

 processes at the tip of the abdomen. 



Of the British Aphides one of the largest and 

 most remarkable is the Aphis Salicis, which is 

 found on the different kinds of Willows, and is 

 nearly a quarter of an inch in length, and of a 

 yellowish grey colour, spotted with black. When 

 bruised these insects stain the fingers of a red 

 colour. Towards the end of September, accord- 

 ing to the observations of Mr. Curtis, multitudes 

 of the full grown insects of this species, both 

 winged and others, desert the willows on which 

 they feed, and ramble over every neighbouring 

 object in such numbers that we can handle no- 

 thing in their vicinity without crushing some of 

 them j while those in a younger or less advanced 

 state still remain in large masses upon the trees.. 



Aphis MiUefolii of Degeer, or the Yarrow Aphis 



