178 



KNOWLEDGE. 



[August 1, 1895. 



under the bark of trees, under stones, or in any other of 

 the thousand and one hiding-places easily discoverable by 

 an enterprising creature, gifted with a triple locomotive 

 power, in walking, leaping and flying. 



Considering the insignificant size of the beetles, and the 

 really minute quantity of matter which, at the most 

 extravagant computation, must be sufficient to serve them 

 as provisions for a lifetime, it is difficult to realize the 

 possibility of their becoming a serious nuisance to agri- 

 culturists ; and, indeed, it is only under special condi- 

 tions that their depredations are of much importance. 

 When we have the plants at their weakest, and the beetles 

 at their strongest, i.e., when the plants are seedlings and 

 the insects fully grown, it is then that the most serious 

 results follow from the attack of the beetles. The mining 

 of the full-grown leaves by the grubs is a matter of very 

 little importance, and in fact can scarcely be detected till 

 the grub has left its tunnel, when the cuticle forming its 

 roof becomes dry and discoloured. But if tlie beetles 

 happen to be in the perfect condition just when a young 

 crop of turnips are appearing above ground, they will at 

 once attack the cotyledons or seed-leaves, and speedily 

 ruin the plant by weakening it and cutting off its supplies. 

 But after the plant has reached a certain size, it has 

 vitality enough to enable it to withstand the damage, 

 which with the large size of the plant is, of course, pro- 

 portionately less, and hence the attacks of the beetles are 

 not of so much consequence. 



If the insects confined themselves to cultivated plants, 

 it would no doubt be easier to take measures against them ; 

 but this is not the case. They are found naturally on 

 many wild cruciferous plants, such as charlock, hedge 

 mustard, etc. ; but if a crop of turnips springs up in the 

 neighboiu-hood, they will not be long in discovering the 

 fact, and speedily forsake their natural food for the more 

 luxuriant supply man has provided. It seems likely that 

 they are guided by scent, for they have been observed 

 advancing in great numbers towards a newly- appearing 

 turnip crop mjainst the wind. In warm weather they 

 readily take to the wing, but as the temperature falls they 

 become less active. Their favourite method of locomotion 

 is certainly leaping, and they can cover about eighteen 

 inches at a single bound. As they are so abundant, so 

 easily travel from place to place, and so readily find other 

 foods when man's supply fails, it follows that a complete 

 extermination from an infected field on a given occasion 

 would not guarantee immunity from the pest a short time 

 afterwards. However many we may destroy, there is 

 always a plentiful residuum lefc amongst the grass and 

 weeds in most uncultivated places, ready to swoop down 

 upon the young crops as soon as they put in an appearance. 

 It is curious that the jaws they use to nibble their holes 

 in the leaves are, though a pair, unlike in shape ; both are 

 strongly toothed (Fig. 4), but one is furnished with three 

 teeth and the other with four. Of 

 course these jaws move laterally, 

 and the pieces, as fast as nibbled 

 off, are helped into the mouth by 

 the rest of the mouth organs, viz., 

 maxillffi and two pairs of palpi. If 

 the head is severed from the body, 

 and placed in a drop of water 

 between two sUps of glass under the microscope, a little 

 pressure on the glass soon causes the jaws to open, when 

 their shape can be seen. 



Several very distinct types may be easily recognized 

 amongst this group of leaping beetles ; they contain also 

 some of the most brilliant of our British insects, and 

 several species, if they were only constructed on a larger 



Fig. 4. — .Jaws of 

 Turnip Flea. 



scale, would easily carry off the palm for splendour. 

 There is a set of brilliant purplish-blue species, constituting 

 the genus llaUica, which are amongst the largest of the 

 group. They are all very much alike, and the discrimina- 

 tion of the species is one of the most trying tests of the 

 patience and acumen of the coleopterist. One of the best 

 known occurs amongst heather, where the beetles are often 

 to be met with in hundreds. Of course, a mere cursory 

 glance will not detect them, but anyone who will take the 

 trouble to sit down amongst the heather and patiently and 

 minutely scrutinize the plants will soon learn to see the 

 brilliant little gems, sitting about here and there, with 

 their hind legs bent beneath them, ready for a spring the 

 moment they are disturbed. Two or three others have 

 shining blue wing-covers and a bright red thorax, a style 

 of ornamentation that is by no means peculiar to this 

 group. On various kinds of willows are to be found, often 

 in swarms, the brilliant species of the genus Cnpidoilera, 

 which exhibit a marvellous play of metallic colours of the 

 most glowing tiuts — coppery, golden green, and the 

 brightest emerald. They are noted also for the regular 

 rows of minute pits, which modify the play of light, and 

 give an added charm of aspect to the wing-covers. Certain 

 species inhabit thistles, and these are generally of a reddish 

 colour ; some of them are extremely globose in form, and 

 with this peculiarity of shape is usually associated an 

 excessive degree of agility. Others prey upon various low 

 plants, such as certain labiates, the rock-rose, woodspurge, 

 mallows, docks, etc. One pretty little polished blue-black 

 species skips about amongst the leaves of the dog-mercury, 

 which it riddles with holes. 



But one of the most remarkable features of the group is 

 the curious structural freaks that are manifested in the 

 hind legs, in addition to the swelling of the thighs. One 

 genus {Pli'ctnisci'lis) is distinguished by having a tooth-hke 

 projection on the outer side of the tibia, or shank, about 

 halfway down (Fig. 5, a). A very abundant species 

 (P. concinna), which is entirely of a bronze colour above, 

 has, by its attacks on hops and turnips, achieved sufficient 

 notoriety to be dignified with more or less appropriate 



Fia. 5.— Hind leg uf (a) Plectroscelis, (b) T/ii/amis, (c) PstiUiodes. 



popular names, such as " hop flea," " brassy turnip flea," 

 "tooth-legged turnip beetle." A peculiarity of a different 

 sort is to be seen in the genus Thyamix or Limgitaraus. This 

 genus comprises an extensive set of small beetles, which 

 are mostly of a pale yellowish, or yellowish-brown colour, 

 and therefore of no great beauty — what one may call a 

 homely and serviceable, rather than an ornamental type of 

 insect. The tarsus, as usual, consists of apparently four, 

 but in reality five joints ; but the basal one is extra- 

 ordinarily long, half as long, indeed, as the entire tibia or 



