THE STUDY OF INSECTS. 
166 
poisonous gas (hydrocyanic-acid gas) is generated within the 
tent. 
A number of useful insects belong to this family. Several 
species furnish dye-stuffs. The best known of these is 
Coccus cacti , the dried bodies of which are known as Cochi¬ 
neal. The stick lac of commerce, from which shell-lac or 
shellac is prepared, is a resinous substance excreted by 
a species, Carieria lacca (Car-ter'i-a lac'ca), which lives on 
the young branches of several tropical trees, and the bodies 
of these insects, which are obtained from the stick lac, furnish 
the coloring agents known as lac dye. China wax is another 
substance for which we are indebted to this family. It is the 
excretion of an insect known as Pe-la, Ericerus pe-la (E-ri- 
ce'rus). In fact many species of this family excrete wax in 
considerable quantities. 
Among the more prominent members of this family are 
the following: 
The Cottony-cushion Scale, Icerya purchasi (I-ce'ry-a 
pur'cha-si).—This beautiful in 
sect (Fig. 203) was at one time 
the most dangerous insect 
pest in California, and did a 
great amount of injury. It is 
an introduced Australian spe¬ 
cies, and has been subdued to 
a great extent by the intro¬ 
duction of an Australian Lady- 
bug, Vcdalia (V e-da'li-a), which 
preys upon it. The body of 
the adult female is scale-like, 
dark orange-red, and has the 
dorsal surface more or less 
lowish-white powder. The in- 
Report for 1880.) 
sect secretes a large egg-sac, which is beautifully ribbed. 
The Mealy-bugs, Dactylopius (Dac-ty-lo'pi-us).—The 
