MUSSEL SCALE. 39 



This species of Scale insect, which may be found at times 

 so thickly coating moderately young bark of the stem and 

 branches of the Apple tree as almost to cover the surface, 

 takes its popular English name with us from its resemblance 

 in shape to our common mussel-shells. In America and 

 elsewhere it is known as the " Oyster-shell " Scale, or "Bark- 

 louse," similarly on account of its resemblance to the shape 

 of an American species of oyster. 



It is very widely distributed, being found in Europe and 

 North America, New Zealand, &c., and infests many kinds of 

 trees and shrubs ; and amongst orchard trees and fruit 

 bushes is to be found on Apple, Pear, Plum, Peach, Apricot, 

 and Currant ; but with us it is a special infestation of Apple 

 bark. 



The injury is caused by the little Cocci, or scale insects, 

 whilst still in active life, inserting their suckers, or proboscis, 

 into the tender bark or young shoots, and thus sucking away 

 the juices, and also doing harm to the tissues by the number 

 of punctures. 



The shape of the larval scale insects when hatched is of a 

 lengthened oval, with a spine at each segment, and at the 

 a,bdominal extremity two long silky appendages, and at each 

 side two lobes ; and the antennae (or horns) are of noticeable 

 length.* They are furnished with eyes, six legs, and a sucker, 

 and run about with great activity for a few days, and then fix 

 themselves, increase in size, and change to the pupal state, in 

 which they are known as " scales." 



These scales are not the true insects, but are shields, or 

 puparia, composed partly of fibrous secretion, partly of the 

 thrown-off insect-skins, and differ slightly in the male and 

 female form. 



The female scales are about the tenth to the eighth of 

 an inch long, usually brown, but sometimes ash-grey or 

 even white, of the shape as figured above by myself from 

 English specimens, elongate, slightly curved, and widened 

 posteriorly, much smaller and of a rusty colour at the other 

 end. The male scales are smaller than those of the female, 

 and straight, or nearly so. 



For the most part the scales adhere firmly to the bark of 

 the infested tree, and on lifting full-grown female specimens 

 the female itself will be found inside, towards the smaller end 

 of the scale (sheltered by it, not fastened to it), the larger end 

 of the scale being filled with fifty or more white oval-shaped 

 eggs. The female resembles a flat fleshy maggot of a pale 

 greyish or yellowish colour, elongate or globular, or, as egg- 



* See " Essai sur les Cochenilles," collective edit, from ' Annales cTe la Soc. 

 Ent. de France,' par Dr. Signoret, vol. i. p. 98 (142). 



