A paper by Mr R Chambers on the subject adduces the additional testimony of facts observed by good naturalists, as Dickson and Curtis the eminent botanists, and Stothard the painter and entomologist, by his own father Mr A. Chambers, and by Joseph Simpson, a fisherman living near Boston, all of which strongly corroborate the probability that some, at least, of the _ignes fatui_ are produced by luminous insects.[154] Mr Main narrates the case of a farmer who stated that he had pursued a Will-o'-the-wisp, and coming up with it had knocked it down, when it proved to be an insect "exactly like a Maggy-long-legs"--that is, the common Crane-fly (_Tipula oleracea_), the very insect with which Mr Sheppard had compared the motions of the luminous flame observed by him.[155] Mr Spence argues that while gaseous emanations may be a cause of stationary _ignes fatui_, the same cause will not explain those which flit along from place to place; and that these are probably luminous insects, however rarely they may have come under the notice of entomologists. "A very strong argument for the possibility of some flying insects being occasionally luminous (in England) is afforded by the facts ... of luminous caterpillars having been within these few years observed for the first time since entomology has been attended to, and that by observers every way competent. If caterpillars so very common as those of _Mamestra oleracea_ may sometimes, though so rarely, be luminous, and if, as Dr Boisduval suggests, and is very probable, this appearance was caused by disease, it is obvious that flying insects may be also occasionally (though seldom) luminous from disease--a supposition which will at once explain the rarity of the occurrence, and the circumstance that insects of such different genera, and even orders, are said to have exhibited this phenomenon."[156] These highly curious facts should make observers cautious in strongly denying statements made by others of phenomena, when they themselves have not been so fortunate as to witness them, even though they may think their opportunities to have been as favourable as those of the _soi-disant_ observer.[157] But we have not yet dismissed Madame Merian. If acquitted of falsehood here, she stands arraigned on a second charge of similar character. In most tropical countries there are found hideous hairy spiders of monstrous size and most repulsive appearance; short-legged, sombre-hued, ferocious marauders of the night, that by day lurk in obscure retreats under stones, or in burrows in the earth.