70 
BRITISH APHIDES, 
§ III. LIFE-HISTOEY AND METAMOE- 
PHOSIS. 
Very generally it will be noticed that Aphides 
abound in such moist and sheltered situations as are 
unvisited by rough draughts of air. They usually 
show a preference to the sunny side of a wood, rather 
than to its northern or eastern aspects. A secluded 
valley, a ravine with its brook of water, a light thicket 
on a hanging hill, or the warm side of a hillock with its 
rank herbage,may be advantageously sought as being the 
favourite haunts of these insects. But although true 
that naked heights are but little visited, some species 
of Aphis are hardy enough to thrive on the stony 
heaths of Scotland and Northumberland, whilst others 
will live almost in the reach of the spray of the sea-shore. 
Thus, Aphis rumicis will multiply on several plants 
which fringe the seaward edge of lofty chalk-cliffs, and 
Mr. Francis Walker speaks also of crowds of Aphides 
which he has seen heaped along the sea-shore,” doubt- 
less having been previously blown into the water from 
the vegetation on the adjacent land. The number of 
species inhabiting a district is found to be governed, 
as might be supposed, by the varied character of its 
flora. Some Aphides affect timber trees exclusively ; 
others feed on soft, succulent vegetables and low herbs ; 
others, again, infest the roots of different grasses, or 
hide under stones and the rotten mortar of old walls. 
Some aquatic plants are very liable to their attacks. 
The water-lily, Nymphoea alba-, sometimes is almost 
killed by the thousands of Bhopalosiphum nymphcece 
which crowd the leaves ; whilst, again, several species 
infest the reed (Arundo) and different sorts of water- 
cress {Nasturtium). 
Violent changes of temperature seem much to check 
the multiplication of Aphides. A cold rain, or the out- 
