Through a pocket lens

by Henry Scherren

He found a beetle covered with these Mites, and on examining them with a hand lens saw that they were attached to their host by a long thread or stalk, which came from the posterior end of the body. Several Mites, he tells us, were joined together by one thread which fastened them all to the beetle; and he came to the conclusion that the parasites were nourished at the expense of the beetle, the thread serving to convey the juices of its body to them.

‘It is very singular,’ he says, ‘to see living insects planted on the body of larger insects, from which they draw their subsistence by means of a thread or stalk.’ And then he goes on to compare these ‘vegetative Mites,’ as he calls them, with the ‘eggs’ of the Water Mites, which he found on Dytiscus and the Water Scorpion. The thread exists, and the Mites are attached by it to their host, but they do not draw nourishment through it from the beetle, for it is composed of their excrements.

The Myriapods are worm-shaped creatures, breathing by means of air-tubes, and furnished with a number of limbs closely resembling each other. There are two groups: the Centipedes and the Millepedes. The former have the body flattened, with one pair of appendages to each segment, the first pair being modified into piercing poison-organs, and they feed on living prey. The body of the Millepedes is round, with two pairs of appendages to each segment; they have no poison-organs, and their food consists chiefly, if not entirely, of vegetable matter.

There seems to be some doubt, however, as to whether Ju´lus, one of the commonest Millepedes, does not occasionally indulge in animal food. In Nature Notes (Jan. 1896) there was a review of the Cambridge Natural History (vol. v). The reviewer, in a brief summary of Mr. Sinclair’s part of the book (the Myriapods), said, after describing the Centipedes: ‘The millepedes, on the contrary, are sluggish vegetarians, with hard, cylindrical bodies, &c.’ On this a correspondent wrote in the March number: ‘Some time ago my attention was attracted to a large earthworm, writhing and twisting about on the garden path, as though in pain, or through having received some injury. On examining it more closely to ascertain the cause of its unusual movements, I found that a millepede had fastened itself to the side of the worm, and appeared to be boring or eating its way into the body, whilst the most violent efforts on the part of the worm were ineffectual in shaking off its antagonist. If the millepede is a vegetarian, what could be its object in attacking so harmless and defenceless a creature as the earthworm? The above, which I take to be a millepede, is the black or dark-coloured creature “with hard, cylindrical body” ordinarily found coiled up in a spiral under stones or rubbish.’

The editor, as a matter of course, referred the matter to the writer of the review. His reply was as follows: ‘If there is no mistake about the identity of the aggressor in the account cited above, the observation is one of considerable interest; for, so far as we are aware, it is the only case on record of a millepede being guilty of such conduct. But were it not for the positive statement that the species was the dark-coloured creature with a hard, cylindrical body, which is ordinarily found coiled up in a spiral under stones or rubbish—a description which exactly applies to the millepedes of the genus Julus—we should have concluded without hesitation that the struggle in question was merely one of those that habitually takes place between the centipedes of the genera Litho´bius or Geoph´ilus and the earthworms upon which they feed.’

Both the Centipedes and Millepedes are shy, light-shunning animals, and if we turn over some stones in the garden or in a walk through the fields we shall probably find specimens enough to serve us in getting some idea of both groups.

The Centipedes are sometimes called ‘Hundred-legs,’ but this implies the possession of many more legs than the creatures really have. In Norfolk and Suffolk the people call them ‘Forty-legs,’ and this is much nearer the mark.

Litho´bius forfica´tus, about an inch long and rufous brown in colour, is extremely abundant under stones and the bark of trees, and in cellars and outhouses. These animals run with great rapidity when disturbed, so that one needs to be on the alert to seize them when they are driven from the places in which they lurk. The body has nine principal and six subsidiary or smaller rings, and there are fifteen pairs of walking legs, besides the first pair, which are modified to serve as poison-organs. De Geer says that he never dared to pick up these Centipedes with ungloved hands, because he had seen a fly, which had been bitten by one, die on the spot, ‘which seems to be a sign that their bite is venomous.’ He examined their modified legs with a good microscope, but could not distinguish any opening. There is, however, an opening, as De Geer suspected, though he could not distinguish it; it lies near the point, and we may also trace the canal through the claw down to the poison-glands which lie, one on each side, at the base of the claws. The mouth parts resemble those of insects, and may be dissected out in the same way. When this Centipede walks, says De Geer, it does not use the last four pairs of legs, but drags them after it; but when it walks backwards, which it does as well as forwards, it then makes use of these four pairs of legs in the same way as the others. If we keep Lithobius alive we shall see that it can walk backwards, though it can scarcely be said to go as well one way as the other. From the same old writer some useful hints as to the method of keeping these animals may be gathered. Those that he kept in a vessel without any moisture soon died, and were quite dried up in twenty-four hours, which will teach us to keep them in a vessel with damp earth, shaded from light and heat.

Dr. Sharp[39] gives some interesting details about the breeding habits of Lithobius, and describes, for the first time, the uses of the two hooks on the under surface of the body of the female.

He experimented with Centipedes and Millepedes. Keeping them in large shallow glass vessels, the bottom of which was covered with a layer of earth, he fed the specimens of Lithobius on insects and worms, and sometimes on raw chopped meat, but they did not thrive on this as they did on prey which they could kill for themselves.