Janiaky, 1902.] 



KNOWLEDGE 



consists of the roots of plants, and during the latter part 

 of one summer, the whole of a second, and the fii-st part 

 of a third, tliey spend their time in nibbling these root-s, 

 whereby they of coiu'sc either seriously weaken or 

 altogetlier destroy the plants attacked. The amount of 

 damage, tiiereforc, that one of these ginibs can do during 

 its two years' course and more, is very considerable, and 

 as the work of devastation is all c;u-ried on beneath the 

 surface of the ground and thus out of sight, its prc^ 

 vention is coiTespondingly difficult. JIan. in fact, must 

 rely largely upon workers whose senses are more acute 

 than his o\v^l if these grubs are to be detected in their 

 clandestine work. And here it is that the rooks and 

 jackdaws aforesaid come in useful, their acute sense of 

 hearing enabling them to detect the movements of the 

 grabs as they work their way through the soil, and of 

 their jaws as they enjoy their subterranean repast. In 

 winter the grubs go deeper into the ground, where they 

 will bo out of the reach of sudden changes of 

 temperature. 



In the third year of its existence, the grub is full- 

 grown (Fig. 5) and about an inch and a half long, with 

 a shiny chestnutrcoloured head, and three pairs of legs 

 similarly colourcKl. The hinder part of the body is 

 always bent round in a semi-circle towards the head, 

 and is very much swollen, the dark-coloured cont^ents of 

 the intestines showing plainly through the thin skin. 

 When tlie giiibs arc quite young, the damage they do 

 is inconsiderable, and is confined to the tenderer and 

 more delicate I'oot fibres, but dui'ing their second and 

 third years they are exceedingly voracious and devour 

 an enormous amount of food, not neglecting even the 

 coai-scr root fibres which had before been too much for 

 their jaws. There is probably a certain small balance 

 of agricultural benefit to be set over against the damage 

 they commit, because their tunnelling niovcmentsi serve 

 to loosen the soil, and while they are devouring their 

 proper food, they necessarily swallow a good deal of 

 oai-th and so perfonn sei-vices analogous to those rendered 

 by earthwonns. 



lu the July of its third summer, the grab goes down 

 to a depth of about two feet and there excavates an 

 oval cell, which it lines with a gummy secretion. Here, 

 throwing off its last lai-val skin, it changes into a 

 ehi-ysalis, which, like those of beetles generally, shows 

 plainly all the parts of the future insect — legs, wings 

 and antenna?, bent round to its under surface and tightly 

 enclosed in a thin skin. The chrysalis stage is a very 

 brief one, lasting only for about a month. Then another 

 and final moult takes place, and the insect appears a 

 full-gi-own and perfectly formed, though soft^skinncd, 

 cockchafer. By the end of August, tlien, or at latest, 

 the beginning of September, it lias completed its cycle 

 of changes, but it is by no means ready for the active 

 business of adult life. In fact, it remains in its cell 

 underground shut up for the winter, and destined to 

 lie helplessly there in company with its last two cast 

 skins till the genial days of spring summon it to the 

 surface. By about the 20th of April, close upon three 

 years after its mother laid the egg from which it was 

 hatched, its skin has suitably hardened, and it performs 

 its first feat in tunnelling as a perfect insect by making 

 a shaft, up which it travels to the open air and the 

 sight of the country ai'ound, which it thus beholds for 

 the first time in its existence. 



Once above ground, the cockchafer climbs up into 

 trees, having a particular liking for oak, beech, chestnut, 

 poplar, and elm, upon the young leaves of which it now 

 begins to feed. It has still some seven or eight weeks 



to live, and that time, which will be a busy one, has 

 to be spent in providing for the coming generation. 

 Frequent pairings take place, and the intervals between 

 the courtships or egg-layings are spent in feasting, both 

 the sexes recuperating their energies by devouring great 

 quantities of the leaves of the before-mentioned trees, or 

 failing them, of whatever else can be found. Thus the 

 insect, in its early stages a devourer of roots, becomes, 

 when fully grown, addicted to leaves and green herbage 

 generally, a curious change of diet which suggested to 

 an old writer the following quaint reflections: — "This 

 seems one of the wise Contrivances of Nature, that 

 adapts as most proper the Aii-y finer nourishment for 

 the more agile and light Body of the Volatile Insect, 

 while the same Animal, when a dull Reptile Wonn, is 

 sustained by a more gross and terrene Food, more fitting 

 to its slow and heavy Natui-e." Both the sexes ai-e 

 excellent diggers, and the male frequently goes beneath 

 the surface as well as his partner, though for what 

 purpose it is not easy to say. The powerful spurs on 

 the fore-legs, which are always found in digging insects, 

 are no doubt useful in excavating the buiTows. Though 

 most abundant about May or June, the insects may bo 

 found more or less frequently all through the summer, 

 the males being met with, at least in this countiy, much 

 more commonly than the females. The insect has now 

 come to the end of its career ; by the time autumn is 

 over they have disappeared, and it seems that none are 

 left to hibernate. 



The unusual length of the larval life produces a 

 periodicity in the appearance of the adults which has 

 some remarkable features. For example, the adult cock- 

 chafers which were to be found during the now closed 

 season of 1901, were not the descendants of any that 

 might have been seen in the preceding year, but sprang 

 from those which appeared in 1898. These latter laid 

 their eggs in the early summer of 1898, and the grubs 

 lived underground during the years 1898, 1899, and 

 1900, becoming \nipx in July, 1900, and perfect insects 

 in August of the same year, but not appearing above 

 the surface till April, 1901. It appears, therefore, that 

 the swanns of cockchafers should be seen every third 

 year, and this, at least on the Continent, is certainly the 

 case. But the remarkable fact is that the year is not 

 the same one in all pai'ts. For example, Switzerland 

 may be mapped out into three distinct regions, in which 

 the cockchafer year falls on different dates. Thus in 

 the region near Basle, the cockchafer year oecuis when 

 the date of the year divides by three without a re- 

 mainder ; in the Berne district when it divides by three 

 with a remainder of one, and in tlie Uri district when 

 the remainder is two. Thus 1899 was a cockchafer ycai- 

 at Basle, 1900 at Bcnie, and 1901 at Lucerne. Thus it 

 follows that three generations of cockchafer grabs ajro 

 at the present moment living in the soil in different 

 places, destined in their tuni to yield the adult insects 

 of the years 1902, 1903, and 1904. 



Wo have said that the males are more frequently 

 seen than their partners, and this is particularly the 

 case in the pairing season, when large assemblages of 

 males may bo noticed in the evening circling like a 

 swarm of bees round the tops of trees or over the gable- 

 ends of houses. When the insects aie plentiful, they 

 often lose their foothold in the trees in the daytime and 

 drop to the gi'ound, when they are eagerly sought aftor 

 by swine and poultry. In the year 1688, enormous 

 swanns a])pcai-ed in the west of Ireland, and the pigs 

 seem to have flourished upon them. 



Besides the common cockchafer, another insect., of 



