THE GNAT TIPULA. 



553 



I shall end this account of the beetle tribe 

 with the history of an animal which cannot 

 properly be ranked under this species, and yet 

 cannot be more methodically ranged under 

 any other. This is the insect that forms and 

 resides in the gall-nut, the spoils of which are 

 converted to such useful purposes. The gall- 

 insects are bred in a sort of bodies adhering to 

 a kind of oak in Asia, which, differ with re- 

 gard to their colour, size, roughness, smooth- 

 ness, and shape, and which we call galls. 

 They are not fruit, as some have imagined, 

 but preternatural tumours, owing to the wounds 

 given to the buds, leaves, and twigs of the 

 tree, by a kind of insects that lay their eggs 

 within them. This animal is furnished with 

 an implement, by which the female penetrates 

 into the bark of the tree, or into that spot 

 which just begins to bud, and there sheds a 

 drop of corrosive fluid into the cavity. Hav- 

 ing thus formed a receptacle for her eggs, she 

 deposits them in the place, and dies soon after. 

 The heart of the bud being thus wounded, the 

 circulation of the nutritive juice is interrupted, 

 and the fermentation thereof, with the poison 

 injected by the fly, burns the parts adjacent, 

 and then alters the natural colour of the plant. 

 The juice or sap, turned back from its natural 

 course, extravasates, and flows round the egg. 

 After which it swells and dilates by the assis- 

 tance of some bubbles of air, which get ad- 

 mission through the pores of the bark, and 

 which run in the vessels with the sap. The 

 external coat of this excrescence is dried by 

 the air, and grows into a figure, which bears 

 some resemblance to the bow of an arch, or 

 the roundness of a kernel. This little ball 

 receives its nutriment, growth, and vegetation, 

 as the other parts of the tree, by slow degrees, 



very shy in making their tickings ; but if they can be 

 viewed without being alarmed by noise, or moving the 

 place where they are, they will not only beat freely, but 

 even answer any person's beating with his nail. At 

 every stroke their body shakes, or seems affected as by a 

 sudden jerk ; and these jerks succeed each other so 

 quickly, that it requires great steadiness to perceive with 

 the naked eye that the body has any motion. They are 

 scarcely ever heard to beat before July, and never later 

 than the sixteenth of August. It appears strange that so 

 small an insect should be able to make a noise so loud as 

 is frequently to be heard from this ; sometimes equal to 

 that of the strongest beating watch. Dr Derham, who 

 examined and first described this species, says, he had 

 often heard the noise, and in pursuing it found nothing 

 but these insects, which he supposed incapable of pro- 

 ducing it; but one day, by finding that the noise pro- 

 ceeded from a piece of paper loosely folded, and lying in 

 a good light in his study window, he viewed it through, 

 and wkh a microscope observed, to his great astonish- 

 ment, one of them in the very act of beating. In some 

 years they are more numerous than in others, and their 

 ticking is of course more frequently heard. We are in. 

 formed by the ab .ve naturalist, that, during the month 

 uf July, in one particular summer, they scarcely ever 

 erased, either in the day or night. 



and is what we call the gall-nut. The worm 

 that is hatched under this specious vault, finds 

 in the substance of the ball, which is as yet 

 very tender, a substance suitable to its nature ; 

 gnaws and digests it till the time comes for 

 its transformation to a nymph, and from that 

 state of existence changes into a fly. After 

 this, the insect, perceiving itself duly pro- 

 vided with all things requisite, disengages it- 

 self soon from its confinement, and takes its 

 flight into the open air. The case, however, 

 is not similar with respect to the gall-nut that 

 grows in autumn. The cold weather fre- 

 quently comes on before the worm is trans- 

 formed into a fly, or before the fly can pierce 

 through its inclosure. The nut falls with the 

 leaves, and although you may imagine that 

 the fly which lies within is lost, yet in reality 

 it is not so ; on the contrary, its being covered 

 up so close, is the means of its preservation. 

 Thus it spends the winter in a warm house, 

 where every crack and cranny of the nut is 

 well stopped up; and lies buried, as it were, 

 under a heap of leaves, which preserves it from 

 the injuries of the weather. This apartment, 

 however, though so commodious a retreat in the 

 winter, is a perfect prison in the spring. The 

 fly, roused out of its lethargy by the first heats, 

 breaks its way through, and ranges where it 

 pleases. A very small aperture is sufficient, 

 since at this time the fly is but a diminutive 

 creature. Besides, the ringlets whereof its 

 body is composed, dilate, and become pliant in 

 the passage. 



CHAP. VII. 



OF THE GNAT TIPULA. 



THERE are two insects which entirely re- 

 semble each other in their form, and yet wide- 

 ly differ in their habits, manners, and propa- 

 gation. Those who have seen the tipula, or 

 long-legs, and the larger kind of gnat, have 

 most probably mistaken the one for the other; 

 they have often accused the tipula, a harmless 

 insect, of depredations made by the gnat, and 

 the innocent have suffered for the guilty; in- 

 deed the differences in their form are so very 

 minute, that it often requires the assistance of 

 a microscope to distinguish the one from the 

 other: they are both mounted on long legs, 

 both furnished with two wings and a slender 

 body; their heads are large, and they seem to 

 be hump-backed ; the chief and only differ- 

 ence, therefore, is, that the tipula wants a 

 trunk, while the gnat has a large one, which 

 it often ex/erts to very mischievous purposes. 

 The tipula is a harmless peaceful insect, that 

 offers injury to nothing ; the gnat is sanguin- 

 ary and predaceous, ever seeking out for a 

 4 A 



