144 BRANCH ARTHROPODA 



nected with a compound booklet." 1 The sucking beak is three jointed 

 and may or may not be longer than the body. They have prominent com- 

 pound eyes and usually ocelli. The long antennae are from three to seven 

 jointed. Many species have on the sixth segment of the abdomen two 

 tubular processes, long supposed to be the honey tubes, but Kellogg says 

 " from them issues another secretion, not sweetish, about which little is 

 known," and that the "honey-dew" so relished by ants (p. 179) "is 

 now known to be an excretion from the intestine issuing in fine droplets 

 or even spray from the anal opening." It is sometimes produced in large 

 quantities, so that the leaves below the plant lice are coated with it and the 

 walks beneath the trees spotted by it. It is fed upon by bees and wasps 

 as well as by ants. In addition to the "honey-dew," many species secrete 

 another fluid, which is excreted as a liquid through " various small open- 

 ings scattered over the body." This liquid soon hardens into a wax. 

 The total waxy secretion appears as a mass of felted threads or wool, as in 

 the wooly apple aphis, and probably serves as a protection for the soft, 

 defenseless body. 



The aphids are remarkably variable as regards their reproduction sexually 

 or agamically, 2 and as regards their possession of wings, so that the life- 

 history varies not only in different species, but in the same species under 

 different conditions. The eggs are laid in the fall, and from them hatches, 

 in early spring, a colony of wingless individuals which may produce (without 

 pairing) either living young or eggs. This may continue under favorable 

 food supply and temperature for a number of generations. Slingerland, 

 of Cornell University, reared four generations of wingless " agamic " 

 aphids. At any time, especially if food becomes scarce or other conditions 

 unfavorable, winged individuals are likely to appear and fly away to other 

 host plants, where they produce, agamically, new colonies. If temperature 

 becomes low or other unfavorable conditions occur, these asexual individuals 

 produce a brood consisting of both males and females. " The males may 

 be either winged or wingless, but the females are always wingless." These 

 sexual forms pair and produce one or more large fertilized eggs which lies 

 dormant over winter and hatches into a wingless " stem-mother " in the 

 spring, and a series of agamic generations follow. The multiplication of 

 aphids is so rapid that, were it not for predaceous insects, such as lad} T - 

 bird beetles, aphis-lions, and parasitic Hymenop'tera, and for insect-loving 

 birds (see Birds), they would utterly destroy their host plant and ulti- 

 mately starve themselves. Professor Forbes made an estimate of the rate 

 of increase of the " corn-louse," and found that if " all the plant-lice de- 

 scending from a single ' stem-mother ' were to live and reproduce through- 

 out |the year we should have coming from the egg the following spring 

 9,500,000,000,000 young. As each plant-louse measures about 1.4 mm. 

 in length and 0.93 mm. in width, an easy calculation shows that these 

 possible descendants of a single female would, if closely placed end to end, 

 form a procession 7,850,000 miles in length." 



Aphids vary greatly in their feeding habits, many feeding upon the 

 juices of tender leaves, stems, leaf -buds, or blossom-buds, while others 

 suck the juices of tender roots in the soil, and sometimes the same species 

 lives both above and below ground. Above ground they may be fought 

 by strong solutions of soap, by kerosene emulsion, or by a weak solution of 

 nicotin. Since they suck the juices of plants they cannot be affected by 

 poisoning the food. Underground, carbon bisulphid is sometimes used, 



1 Comstock. * Glossary. 



