1 64 INJURIOUS AND USEFUL INSECTS 



be found beneath it a full-grown female insect, alive or dead, 

 according as it is examined in the beginning or the end of 

 winter, and perhaps some twenty or thirty rather large eggs. 

 The scale is in one group of scale-insects merely the body of 

 the female, and shows under a lens the transverse divisions of 

 the segments. In such species the dead body of the parent, 

 becoming dry, hard and arched, conceals and defends the eggs 

 within. But in other species, and the mussel-scale is one of 

 these last, the female secretes from her body a waxy, resinous, 

 or gelatinous substance, often in the form of delicate fibres, 

 which constitute an additional outside envelope. In the 

 mussel-scale the fibres are felted, and form the ghief part of 

 the scale, the cast skin, yellowish in colour, and perhaps dry 

 and shrivelled, forming the narrow tip only. We may remark 

 that the protective secretion varies greatly in different species, 

 and in some cases yields a very useful product ; shellac, out 

 of which sealing-wax and some lacquers are made, and Chinese 

 candle-wax are instances. 



The eggs of the mussel-scale are hatched in early summer 

 (May-June). The issuing larvae are small (3 mm. long) and of 

 yellow colour, with eyes, short, six-jointed legs, and a pair of 

 bristles at the tail-end. They run briskly about the tree for 

 two or three days, then choose their feeding-places, insert 

 the long, boring mouth-bristles, and come to rest. If, as 

 always happens upon apple-trees, they are females, they 

 grow fast, change their skin more than once, and gradually 

 lose their original appearance. The hinder part of the body 

 swells and becomes rounded ; the eyes, antennae, and legs 

 shrivel up ; the waxen shield enlarges enormously. Growth is 

 often but not always completed before winter sets in. The 

 male occurs on broom and heather. Those who have seen it, 

 tell us that the body of the male insect soon ceases to enlarge, 

 and that when full-grown it has only a quarter of the length of 

 the female scale. When this size is attained the male ceases 

 to suck, and the mouth-parts atrophy. Then it enters a 

 resting-stage in which new legs and antennae, and a pair of 

 wings appear as growing rudiments. A true pupa -stage 

 follows, and the insect finally emerges as a minute fly, with 

 two membranous wings, fertilises the female, and perishes. 

 Since males are rare, it is probable that the mussel-scale is 

 ordinarily parthenogenetic (not requiring fertilisation). It will 



