Marvels of the Universe 735 
called the Mussel Scale insect, which has become practically cosmopolitan in its range, having been 
carried on nursery stock from one apple-growing region to another. 
The Scale Insects, or Coccidz, constitute a very remarkable group, most of its members being 
highly injurious from an economic point of view, although a few—such as the Cochineal insect, to 
which reference has already been made—are directly useful to mankind. The Mussel Scale has 
been mentioned chiefly because its metamorphosis is well known and probably more or less typical 
of the life-histories of scale insects in general. If we lift up a large Mussel Scale in winter, and place 
it beneath the microscope, we shall find that it shelters from fifty to one hundred brilliant white eggs. 
At one end of the scale we shall also find the dead and shrivelled remains of the adult female insect. 
In the springtime the eggs hatch, and the minute, six-legged larvee creep from under the scale, 
and roam over the twigs and branches. Each eventually settles down at a spot where the cuticle 
is tender, inserts its “ beak,’ and begins to pump up the life-blood—z.e., the sap—of the tree. Of 
course, the amount of sap extracted by the individual scale insect is infinitesimal ; but when, as is 
commonly the case, millions of the pest are working together, the loss to the tree is very serious. 
Not infrequently the scales are found upon the leaves, and occasionally upon the fruit. One scale 
insect, closely related to that of the apple, may frequently be found upon the skin of oranges. 
The larve, when once settled, become sedentary in the fullest sense of the word. Each begins 
to secrete a waxy substance, which rapidly hardens and forms the shell or scale. This grows by 
successive layers of secretion as the insect increases in size. The female larva of the Mussel Scale 
insect eventually becomes an inert, grub-like creature, which never leaves the scale, but perishes 
therein after depositing its eggs. The final moult of the male larva, however, is preceded by a kind 
of pupa state, and eventually the adult insect issues from the scale as a minute “ fly’ with long 
Mak 
Photos by] [Harold Bastin. 
SCALE INSECTS. 
To the left is a branch covered with Ash Scales, nearer to the right are two bearing a number of Willow Scale-insects, 
while the right-hand photograph is of the Mussel Scale. They are shown a little less than natural size. 
