of 



crawling. The species reside in great so- 

 cieties upon almost every species of plant, 

 of which they suck the young shoots, leaves, 

 and stems, by the assistance of their pro- 

 boscis, producing disease in the plant either 

 by greatly weakening it, or by raising 

 vesicles, or other gall-like excrescences, in 

 which whole generations of Aphides reside. 

 The anal tubercles above mentioned secrete 

 a saccharine fluid of which ants are very 

 fond ; and it is this fluid dropped upon the 

 adjacent leaves, or the extravasated sap flow- 

 ing from the wounds caused by the punctures 

 of the insects, which is known under the 

 name of the honey-dew. In the spring they 

 are viviparous, in the autumn and as 

 winter approaches they are oviparous ; and 

 by a surprising aberration from the common 

 laws of nature, it appears that one im- 

 pregnation of the female is sufficient for 

 many generations, without further assistance 

 from the male. All the Aphides which 

 appear in the spring are exclusively females, 

 no males being found till the autumn ; and 

 the females are endowed with such astonish- 

 ing fecundity, that nine generations each 

 generation averaging 100 individuals have 

 been produced within three months ; " so 

 that from a single Aphis, 10,000 million 

 millions may be generated in that short 

 period I " In some years they re BO nume- 



PLANT-LICK. (APHIS PLATANOIDES.) 



rous as to cause almost a total failure of the 

 hop plantations ; at other times the beans, 

 peas, and potatoes are injured by them to 

 an alarming extent ; as also are numerous 

 shrubs, and plants, including the delicate 

 exotics raised in stoves and green-houses. 

 There are numerous species ; uniformly de- 

 riving their specific name from the tree, 

 shrub, or plant, on which thev are common- 

 ly found. Of these the Aphis rapce, which 

 has made a great noise as the Aphis vastator 

 and feeds on various plants, the Aphis rosce 

 (or rose louse), the Aphis hurnuli (or hop- 

 fly), and the Aphis vitis (or vine-fretter), are 

 among the best known and most destructive; 

 but the largest and most remarkable of 

 the British Aphides is the Aphis salicis, 

 which is found on the different kinds of 

 willows, and is nearly a quarter of an inch 

 long. Many of the species have the body 

 densely clothed with a white cottony secre- 

 tion, either in threads or flakes ; among these 

 j may be particularly mentioned the Aphis 



lanigera, or American blight, as it is termed, 

 which infests the stems of Apple-trees, some- 

 times totally destroying them. 



" The injuries occasioned by plant lice," 

 as Dr. Harris very truly observes, " are much 

 greater than would at first sight be expected 

 from the small size and extreme weakness 

 of the insects ; but these make up by their 

 numbers what they want in strength in- 

 dividually, and thus become formidable 

 enemies to vegetation. By their punctures, 

 and the quantity of sap which they draw 

 from the leaves, the functions of these im- 

 portant organs are deranged or interrupted, 

 the food of the plant, which is there elabo- 

 rated to nourish the stem and mature the 

 fruit, is withdrawn before it can reach its 

 proper destination, or is contaminated and 

 left in a state unfitted to supply the wants 

 of vegetation. Plants are differently affected 

 by these insects. Some wither and cease to 

 grow, their leaves and stems put on a sickly 

 appearance and soon die from exhaustion. 

 Others, though not killed, are greatly im- 

 peded in their growth, and their tender 

 parts, which are attacked, become stunted, 

 curled, or warped. The punctures of these 

 lice seem to poison some plants, and affect 

 others in a most singular manner, producing 

 warts or swellings, which are sometimes solid 

 and sometimes hollow, and contain in their 

 interior a swarm of lice, the descendants of 

 a single individual, whose punctures were 

 the original cause of the tumor. I have 

 seen reddish tumors of this kind, as big as a 

 pigeon's egg, growing upon leaves, to which 

 they were attached by a slender neck, and 

 containing thousands of small lice in their 

 interior. Naturalists call these tumors galls, 

 because they seem to be formed in the same 

 way as the oak-galls which are used in the 

 making of ink. The lice which inhabit or 

 produce them generally differ from the others, 

 in having shorter antennae, being without 

 honey-tubes, and in frequently being clothed 

 with a kind of white down, which, however, 

 disappears when the insects become winged." 



Mr. Knapp, in his ' Journal of a Natura- 

 list,' has thus described this species, and its 

 effects. " Our apple-trees here are greatly 

 injured, and some annually destroyed, by 

 the agency of what seems to be a very feeble 

 insect. We call it, from habit, or from some 

 unassigned cause, the ' American blight.' 

 [It seems, however, that it had been noticed 

 in England as early as the year 1787 ; and 

 there is good reason to believe that in 

 America it is not indigenous, but was in- 

 troduced there with fruit-trees from Europe.] 

 In the spring of the year a slight hoariuess 

 is observed upon the branches of certain 

 species of our orchard fruit. As the season 

 advances this hoariness increases, it becomes 

 cottony ; or, in other words, towards the end 

 of summer the under sides of some of the 

 branches are invested with a thick, downy 

 substance, so long as at times to be sensibly 

 agitated by the air. Upon examining this 

 substance, we find that it conceals a multi- 

 tude of small wingless creatures, which are 

 busily employed in preying upon the limb 

 of the tree beneath. This they are well 

 enabled to do, by means of a beak termina- 



