RH.YNCHOTA. 



199 



SPRUCE-GALL APHID (Chermes abietis). 

 Larva ; b, An older larva with its moulded skin still 

 attached to it ; c, Winged insect ; d, The gall. (All 

 enlarged.) 



provided with one pair of wings ; the hind- wings being rudimentary or altogether 



absent ; they have rather long antennae, distinct eyes, . and, in some cases, are 



furnished with two long bristle -like 



tails. These winged males are very 



rarely seen, which is accounted for by 



the fact that their mouth -parts are 



atrophied, so that they are incapable of 



taking nourishment, and live only a 



short time. The females are always 



wingless, and usually remain fixed to 



one spot, with their beak buried in the 



tissues of the plant, and their back 



often spread out in the form of a shield 



covering the head and body. The beak 



is generally three-jointed, the antennae 



are short, and in the tarsi, which appear 



at first sight to consist of but one joint, 



two or three joints may on close examination be distinguished, the last ending, as 



a rule, in a single claw. In many species the female dies shortly after laying eggs 



beneath her when her body dries up and remains as a protective cover for them. 



When the larvae are hatched they soon leave this shelter, and rove about the food 



plant in search of a suitable place in which to insert their beaks and begin the 



operation of pumping up the sap. They cast their skin several times in the course 



of their growth ; and those which become adult females undergo no great change 



in appearance, beyond an increase in their size, a gradual lengthening of the 



antennae, and a partial or almost complete obliter- 

 ation of the segmentation of their bodies. With 

 the male larvae the case is different ; these, unlike 

 all others belonging to the order, undergoing a true 

 metamorphosis before reaching the perfect state. 

 Each prepares for itself a sort of cocoon, and 

 it becomes transformed into a quiescent pupa, 

 from which, after a certain lapse of time, the 

 winged insect emerges. In Orthezia and other 

 genera the female, instead of keeping to one spot 

 on the food-plant, moves about and taps it at 

 different points in order to extract the sap. 

 When the eggs are laid, she envelops them in 

 a kind of white cottony secretion and leaves 

 them. Some species penetrate beneath the 

 epidermis of their food -plant, and often cause 

 the formation of galls, which, growing up around 

 them, sometimes take the most extraordinary 



shapes. Scale-insects are probably more numerous within the tropics than in more 



temperate regions, although comparatively few of these tropical species have been 



described. These insects are found on the bark and leaves, and sometimes 



^-i^|2iW 



FEMALE OF Orthezia urticce (nat. size). 



