It is interesting to note how the woodlice in winter simply remain where they happen to be so long as there is sufficient moisture, though they are ready to run about as rapidly, for a time, as in summer, should they happen to be disturbed.
No doubt many points of inter-relation between woodlice and other animals remain to be discovered. Mr. John W. Odell tells us that on Exmoor, in the open, he found no Armadillidia, though other forms occurred under nine out of every ten stones that he turned over, and here the smaller species of ants also abounded. Close to stone walls Armadillidia were to be seen to the exclusion of all other genera, and this state of affairs was ascribed by Mr. Odell to the presence of swarms of the large wood-ants which he considers would make short work of any woodlice that could not protect themselves by rolling up.
We ought not to conclude this account without mentioning the fact that woodlice once played an important part in medicine.
Doctor Fernie (28) gives some interesting extracts with regard to the hog-louse and the woodlouse. The latter he seems to have identified quite correctly as Oniscus asellus. He calls the former, however, indiscriminately, "the common armadillo" (which is the old name for the pill-woodlice now known as Armadillidium), "the pill millipede" and "Glomeris marginata." The last two names are those of another creature, not a crustacean, which when it is rolled up can be very easily mistaken for an Armadillidium, though, when it uncurls, it will be seen to have many more than seven pairs of legs. The local appellations applied to the hog-louse by Doctor Fernie, and his remarks with regard to its commonness, tend to show that it is Armadillidium vulgare, to which he really refers, and the use of which in medicine was commonly general.
Hog-lice were prescribed for scrofulous diseases and obstructions of the liver and digestive organs, among other things, and the London College of Physicians directed that the creatures should be prepared by suspending them in a thin canvas bag placed within a covered vessel over the steam of hot spirit or wine, so that being killed by the spirit they might become friable. Hog-lice and Woodlice were also administered alive, while the former were also put down the throats of cows "to promote the restoration" of their cud, hence their name of "cud-worm." There seems to be considerable evidence that even in modern times Woodlice have had considerable remedial effect which depends upon "an alkalescent fluid" contained in them.
Local Names.—Among the local names by which these creatures are known are those of "sow bug," "lucre pig" (Berkshire), "carpenter" and "chiselhog" (Berkshire). Doctor Fernie (28) gives a number of others:—"thrush-louse," "tiggyhog," "cheslip," "kitchenball," "chiselbob," "lugdor," "palmer," and "cudworm." In the eastern counties the same writer notes that they are known as "old-sows" or "St. Anthony's hogs" while the Welsh call them "little grey-hogs," "the little old women of the wood" or "grammar-sows," grammar signifying a shrivelled up old dame. Oniscus asellus was sometimes called "socchetre," "church louse," and "chinch."
Methods of Collection and Preservation.—Woodlice should be collected straightway into tubes or bottles half filled with 30 per cent. methylated spirit.[3] Woodlice dropped into this weak spirit become gradually narcotised and die, and they remain limp enough for purposes of examination or to allow, of their legs and antennæ being set out during the process of mounting. Specimens to be kept permanently should be placed in 70 per cent. alcohol. For storage purposes the specimens of each species from a given locality should be put together into a small flat bottomed tube such as is used for pillules by apothecaries or specially made for natural history purposes. A paper label on which the name, locality, date of capture and any other necessary particulars have been written with dark lead pencil, is not affected by the spirit. The tubes may be corked, though if not frequently examined all the spirit may evaporate, and cause the specimens to be spoilt. A safer method is to plug the tubes with cotton wool and keep all those containing a given species or specimens from a particular locality beneath the surface of spirit in a large wide-mouthed bottle, into which first of all some cotton wool has been put to prevent the tubes from coming into sudden contact with the glass at the bottom. For show purposes in museums, specimens taken direct from 30 per cent. spirit should be mounted on slips of opal glass by means of gum-tragacanth which has been powdered and shaken up in spirit before having water added to it. The slips can be exhibited in glass tubes, six inches high by one across, or in narrow stoppered museum jars. A variation of the method is to mount the animals on clear glass and to place behind them another strip of any colour that may be preferred.
Classification.—The various genera of woodlice are connected together so closely, by intermediate forms, that their division into families is, to a very great extent, arbitrary. Bate and Westwood described but a single family Oniscidæ (I), though they distinguished two sub-families:—Ligiinæ, which included the forms with many joints to the flagellum of the antenna, and Oniscinæ, which contained the rest.
Since then the pill-woodlice have been thought by some to be sufficiently different from the other genera to warrant their separation, and three families namely, Ligiidæ, Oniscidæ, and Armadillidæ have been recognized, as for instance by Dr. Scharff (63).
A fourth family—Trichoniscidæ—has been added by Professor G. O. Sars, who in his Crustacea of Norway (59) alludes to the division of the tribe into the sections Ligiæ and Onisci and has adopted the following classification:—