382 TRANSFORMATIONS OF INSECTS. 
and the sudden appearance of thousands of these insects upon 
different plants. Fortunately they have a crowd of enemies, other- 
wise they would do a vast amount of harm to vegetation. They 
are found on almost every kind of plant, and upwards of three 
hundred species have been described. The hop Aphis sometimes 
nearly ruins the crop, and the rose Affis, and that which is 
found on the scented geranium also do much mischief. The 
COCHINEAL INSECT. (Magnified.) 
larve of the Coccinelle, or lady birds, and several /chneumous, 
devour and kill great numbers. 
The engraving on page 380 shows two immature females and 
a male which has wings. 
The mischief done by these insects is produced by their 
tapping the delicate tissues of the plants with their suckers, and 
by their extracting the richest sap. They congregate in groups 
on the stems and leaves, but in the autumn the last generations 
emigrate from plant to plant. 
Some of the Aphides which belong to the genus Lachnuus do a 
great deal of harm to apple trees; they are well known from the 
