78 
BRITISH GALLS 
millions of stout men—that is, more than the whole popula¬ 
tion of China.” It is generally held that Huxley’s estimate 
was below the mark ! Luckily, they have numerous enemies 
which keep them well in check, but many species are often 
serious pests in gardens. The generation with which 
gardeners are mostly familiar is the parthenogenetic young 
produced by wingless females hatched from eggs laid in the 
previous autumn. The production of living young by 
females without male intervention may go on for several 
generations. Later in the year, coincident with decreased 
food-supply and lowering of the temperature, sexual insects 
are produced, and the females deposit fertilized eggs, which 
yield wingless females in spring. These apterous viviparous 
females are often termed “ mother queens ” ; they are also 
spoken of as “ fundatrices.” In the classified catalogue of 
galls at the end of this book the expression “ Aphis ” refers to 
the apterous viviparous female. Metamorphosis often takes 
place amongst the parthenogenetic generations, and the 
habits are very varied. It is the rule, however, that winged 
forms appear when food is scarce, and wingless females are 
usually the sexually perfect ones. Many Aphides produce 
enormous quantities of a sweet sticky substance known as 
“ honey-dew,” which is emitted through two tubes or 
“ cornicles ” situated on the back. Kirby and Spence 
remarked : “ You have doubtless observed what is called 
the honey-dew upon the Maple and other trees, concerning 
which the learned Roman naturalist Pliny gravely hesitates 
whether he shall call it the sweat of the heavens, the saliva 
of the stars, or a liquid produced by the purgation of the 
air. Perhaps you may be aware that it is a secretion of 
Aphides, whose excrement has the privilege of emulating 
sugar and honey in sweetness and purity. ... It issues in 
liquid drops from the abdomen of these insects, not only by 
the ordinary passage, but also by two setiform tubes placed 
one on each side just above it.” 
Probably the best-known of all aphid galls are those 
caused by species of Chernies on the Common Spruce Fir. 
