270 NATURAL HISTORY OF THE FARM 
from within. These thus escape poisons deposited upon the 
surface of the plant, and are killed by spraying only when 
some contact in- 
secticide (like kero- 
sene emulsion, or 
various prepara- 
tions of nicotine, 
etc.) is thrown upon 
their bodies. 
Both types of 
feeders we often find 
side by side. We go 
Fic. 110. A colony of aphids on a leaf of Ceanothus; . 
h, a syrphus-fly larva, feeding; 7, a winged aphid; intoacabbage-field, 
j, t attending th 1 sk, aphid parasitize i" 7 
j, an ant attending the colony an aphid p where tittle white 
(see fig. 113). 
butterflies flutter 
above the rows, and we find their green larvae, ‘“‘cabbage- 
worms,” stretched at length upon the surfaces of the leaves, 
placidly eating out scallops in the margins. On loose cab- 
bage leaves we find whole colonies of 
minute gray-green aphids, ‘“‘cabbage- 
lice’, sucking the sap out of the 
leaves and making them buckle and 
curl. 
Most herbivorous insects are very _ Belgie eels yaa 
limited in the range of their diet. ladybind beclle aed its 
They will feed upon the plants of but ae 
a few species—usually closely related species. The common 
potato-beetle eats other things besides potato, but only a 
few other species of the same genus—other solanums. This 
is, for the husbandman, a very fortu- 
nate limitation. 
The worst of our field and garden 
pests are species of insects from 
ee dy te Me other lands. They have been brought 
