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 



FIG. 110. A colony of aphids on a leaf of Ceanolhus; . , 



h, a syrphus-fly larva, feeding; , a winged aphid; into a Cabbage-field, 

 j, an ant attending the colony; k, an aphid parasitized , ... 



(see fig. 113). where little white 



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 

 limited in the range of their diet. 

 They will feed upon the plants of but 

 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 

 other lands. They have been brought 



PIG. 111. The nine-spottad 

 ladybird beetle and its 

 larva. 



