226 DR. JOftNSTON ON THE ACARIDES OP BERWICKSHIRK. 



The threads of its web are secreted from a conical nipple 

 situated underneath and very near the extremity of the abdo- 

 men. They are drawn out and guided by the motions of 

 the insect and by the action of the minute claws of the legs, 

 which seem to be only used for this purpose. The threads 

 are so slender that we fail to see them even with the assistance 

 of a magnifier until after they are woven into a Aveb or net- 

 work. In the construction of this web all the feet are moved 

 with great agility and qufckness, but the movements of the 

 mite itself are not quick, and it walks with difficulty over 

 smooth and polished surfaces, as over glass. Upon leaves, 

 especially on the under face of them, it finds a fitter hold, 

 for supported on the bristles that jut out beyond the tarsal 

 joint, it crawls over the uneven surface with ease. Here 

 it busies itself in spinning its web by affixing the threads 

 to the prominences and hairs of the leaf ; and under this 

 shelter a colony, consisting of many of both sexes in matu- 

 rity and of young in all their ages, feed at full and multiply 

 with rapidity their evil race. The plant shows their influ- 

 ence in its sickly yellow hue ; the 5ap is sucked by myriad 

 insect-mouths from the vessels of the leaf, and its pores are 

 choked by excremential fluids, — and the gardener mourns the 

 inefficacy of his remedies and the loss of his cherished 

 flowers. There are, indeed, destructive enemies to them in 

 their own class, but which the gardener cannot call to his 

 aid, for they obey one only Master. A mite named by Dugbs 

 Dermanyssus feeds on them ; and the grub or larvae of the 

 Hemerobiidae or pearl-flies, (the same which prey on the 

 Aphides,) devour them in such numbers and so fast that en- 

 tire colonies quickly disappear before them. In half a mi- 

 nute the ravenous grub will suck the life out of the largest 

 Aphis ; and hence imagine in what short measure of time it 

 will exhaust the vital juices of these least minims of crea- 

 tion !♦ 



The egg of this mite is spherical, colourless, and propor- 

 tionably large. The larva which comes from it is minute, 



• " He found the polish'd glass, whose small convex 

 Enlarges to ten millions of degrees 

 The Mile, invisible else, of Nature's hand 

 Least animal." — Phili1»si, Cider, Bk. i. 



