342 



♦ KNOWLEDGE ♦ 



[April 24, 1885. 



floating 2^ miles above the eaitli's surface over the whole 

 lone foreshortened into the circumference aeh d the sun's 

 light would be wholly lost. Something like this must have 

 been the state of things when Kepler, WoUaston, and others 

 saw the dark lunar eclipses which have been recorded by 

 them. It is easily seen that the range of possible illumina- 

 tion varies from absolute darkness to some thirty times full 

 earthlight, or more than 400 times full moonlight. Pos- 

 sibly taking into account the circumstance that there is 

 only one point on the moon's disc where the eclipse is abso- 

 lutely central, we may get, under very favourable condi- 

 tions, 500 times full moonlight from a (so-called) totally 

 eclipsed moon. 



• r- 



Since the above paper was begun, several weeks since, 

 I have observed that Mr. Baxendell has endorsed (at a 

 meeting of the Astronomical Society of Liverpool) Mr. 

 Williams's mistake. 



OUR HOUSEHOLD INSECTS. 



By E. a. Butler. 



COLEOPTERA {coniinued). 



THOUGH Xeslobium tessellatum is the principal beetle 

 which, in this country, has been identified with 

 Death-watch tickings, it is not alone in this claim to the 

 character of harbinger of death ; Anohium douiesticum also 

 ticks, and has, no doubt, scared many a rustic equally with 

 Xeslobium. Ono entomologist, at least — the indefatigable 

 Professor Westwood — once kept a regular diary of its tick- 

 ings, the particular specimens whose doings were chronicled 

 being inhabitants of a wooden mantel in the Professor's 

 study ; they ticked at intervals during the winter months 

 as well as at other seasons, though at such times the noises 

 could scarcely have been intended, as they probably are 

 iluring the warmer months, as an exchange of compliments 

 between love sick couples. 



Notwithstanding the obscurity and retirement of their 

 life, these wood-boring beetles have not managed to escape 

 the attacks of parasites. Several species of ichneumon flies 

 and other allied insects prey upon them, and the delicate 

 little gauzy-winged persecutors may sometimes be seen run- 

 ning about hither and thither over Anobium-infested wood, 

 in maternal anxiety to find a suitable nidus for their brood. 

 Some, too large to enter the burrows, are furnished with a 

 long ovipositor with which to reach their victim?, into 

 whose bodies they insert their eggs. Others are small 

 enough to enter the burrows bodily, and hunt their prey 

 like a ferret after a rabbit. One of these latter, Theocolax 

 formiciformis, superficially something like a minute ant, 

 in consequence of the absence of wings, I have obtained in 

 considerable uuoibers from a colony of Anohium domcsticum 

 which had established themselves in an old aquarium 

 stand. 



Yet another member of this family of wood-borers, of 

 very similar appearance to Anobium, sometimes does con- 

 siderable damage to woodwork. It is especially partial to 

 willow-wood, in which it makes neat cylindrical burrows. 

 It is called I'tilinus pectinicornis (Fig. 1), and the specific 

 name refers to a remarkable peculiarity in the antennoe of 

 the male, the sex which, for a reason that will appear pre- 

 sently, is most commonly seen. It may be recognised by 

 its extremely cylindrical reddish-brown body and rather 

 swollen black thorax. The antonnaj are marvellously beau- 

 tiful ; instead of being composed of a mere string of simple 

 joints, such as constitute those of the allied species, and, in 

 fact, of beetles in general, they appear, when fully spread 



out, like two pieces of deep fringe. This results from each 

 joint, except the two at the base and the one at the apex, 

 carrying a lateral appendage generally far longer tiian 

 itself. The apical joint is itself of the same form as these 

 appendages, so that altogether there are nine of them ; but 

 the one nearest the base is much shorter than the rest, and 

 seems little more than like a stout tooth, while the last 

 seven, which are of nearly equal length, are several times 

 as long as the joints to which they belong. Antennae of a 

 similar character occur in a few other British beetles, 

 though in none is the peculiarity so greatly exaggerated as 

 in the present species. 



It is not easy to conjecture the raison d'etre of this re- 

 markable feature, for there seems to be little in the habits 

 of the insect to account for its differing from its congeners 

 in 80 peculiar a way. It can scarcely be merely a sexual 

 distinction, but seems to point to some greater acuteness in 

 the organs of sense, perhaps necessitated by the fact that 

 the female rarely leaves her burrows, only advancing to the 

 entrance thereof to receive the addresses of her lord and 

 master, who, on his part, remains on the outside, and con- 

 ducts his courtship from that position. It is a curious fact 

 that the males of certain moths, which have similarly 

 complex antenna;, possess also a marvellous power, quite 

 independent of sight, of detecting, even from great distances, 

 the presence of a virgin female of their own species. 





Fig. 1. Ptilinus pectinicornis (male). 



Ptilinus is sometimes terribly destructive to timber, and 

 apparently the most remarkable instance on record of this 

 undesirable characteristic is one given by Westwood, who 

 states that a perfectly new bed-post (those were the days of 

 the great four-posters that lumbered up our fathers' bed- 

 chambers) was, in the space of three years, completely 

 destroyed by countless numbers of these insects. But 

 such depredations are necessarily becoming more and more 

 things of the past, and in these days of iron bedsteads, &c., 

 Ptilinus, and others of that ilk, must be beginning to find 

 that they have fallen on evil times, and that the conditions 

 of life are not nearly so favourable as they used to be in 

 the happy days of old. I have found it also in a printing- 

 office, where, in the abundance of wooden " plant " stored 

 up, it must have discovered a perfect mine of wealth. 



Anobium domesticum is not the only representative of 

 tliAxt genus in our household fauna ; another is A. paniceum, 

 a shorter and broader insect of somewhat paler colour. It 

 is almost omnivorous in its tastes, attacking any sort of 

 vegetable substance that may fall in its way, though less 

 of a wood-borer than its relative ; such things as dry 

 bread, biscuits, rhubarb root, ginger, wafers, and even so 

 unlikely a substance as Cayenne pepper, have been 

 greedily devoured by it, and it has also not unfrequently 

 attacked ship's biscuits, riddling them through and through, 

 and damaging them to such an extent as to render them 

 quite unfit for human food. Nor does it make any differ- 

 ence if the vegetable matter is not in its primitive con- 



