170 PLANT LICE. 
Another species occurring on the under side of twigs of 
hawthorn was described by Prof. Oestlund as Sch. crategi. He 
says that it is found during September in an almost continuous 
row on the under side of every twig, and that it is very con- 
spicuous from the flocculent covering of the apterous form. 
Sch. corni Fab. occurs during September and October in 
great numbers on the underside of the leaves of the dogwood. 
Sch. panicola Thomas is found on the roots of some grasses, 
as Panicum glabrum, Setaria glauca and others. 
In the northern part of the state we find another very 
peculiar species on the under side of the branches of the alder, 
which always attracts the attention of observing persons. 
Schizoneura tessellata Fitch. (The Alder-blight). 
Wherever these insects are at all numerous they form large 
patches of a snow-white down. By removing this delicate cov- 
ering we find wingless individuals of a dull bluish black; the 
back of the segments are marked with strongly impressed lines, 
and are covered with white down in square, checker-like spots. 
The louse is fairly large, measuring 0.16 of an inch in length. 
They secrete an abundant supply of honey-dew, which of course 
attracts ants. It is so abundant that the foliage beneath the lice 
is coated with it; upon it black fungi grow. Another curious 
fungus grows in large spongy masses immediately beneath the 
cluster of plant-lice, being evidently fed by the honey-dew that 
falls upon it. 
Nothwithstanding the protecting covering or white down, 
many of these lice are eaten by the larve of a fly, even the cater- 
pillar of a butterfly finds it to its taste. 
Other species of this interesting genus might be mentioned, 
but all of them are of less importance than the following species, 
which can become very injurious to our apple trees; and buyers 
of young trees from nurseries should keep their eyes open, so 
that they do not introduce it into their orchard. This warning 
is important, as the entomologist knows positively that such dan- 
gerous insects have been shipped from nurseries to their cus- 
tomers, and once introduced it is not easy to eradicate them, as 
will be seen by reading their peculiar life-history. 
