Huber says that he has ascertained by a great number of observations that electricity is singularly favourable to the secretion of the substance of which honey is formed by flowers; the bees never collect it in greater abundance, nor is the formation of wax ever more active, than when the wind is in the south, the air humid and warm, and a storm gathering[661].
viii. Wax generally transpires through the pores of the skin of those insects that produce it, either partially or generally, and it is secreted from honey or other saccharine substances taken into the stomach. In the hive-bee, as has been before stated, it is produced partially[662], but in many other insects it is a general transudation of the body. This is particularly the case with a large number of the Homopterous Hemiptera; and those flocoons that look like cotton, and cover the body of several Chermes and Aphides, if closely examined will be found of the nature of wax: this I have particularly noticed with respect to Chermes Fagi, in which the cotton-like flocoons are often so long as to cause the insect to look like a feather, and a leaf covered by them exhibits a very singular appearance, as if clothed with the fine down of a swan[663]. Probably the white powder or threads that appear to transpire through the skin of many other insects is of a waxy nature. In the larva of a beetle described by Reaumur, the flocoons are so arranged as to give the animal some resemblance to a hedgehog, and when rubbed off they are reproduced in twelve hours[664]. Gyllenhal, speaking of Peltis limbata, observes, that when alive it is covered with a white powder resembling mould, which if rubbed off returns again as long as the animal lives[665].
It will not be improper to include under this head what further account I have to give of Lac, which though regarded as a resin, since Cocci sometimes certainly produce wax[666], probably has some analogy with the latter substance. When the females of this Coccus (C. Lacca) have fixed themselves to a part of the branch of the trees on which they feed (Ficus religiosa and indica, Butea frondosa, and Rhamnus Jujuba[667]), a pellucid and glutinous substance begins to exude from the margins of the body, and in the end covers the whole insect with a cell of this substance, which when hardened by exposure to the air becomes lac. So numerous are these insects, and so closely crowded together, that they often entirely cover a branch; and the groups take different shapes, as squares, hexagons, &c., according to the space left round the insect which first began to form its cell. Under these cells the females deposit their eggs, which after a certain period are hatched, and the young ones eat their way out. Though indisputably an animal secretion, many of the properties of lac are not very different from those of the juices of the trees on which the animal feeds, and which therefore would seem to undergo but little alteration.
Wax seems also to form a constituent part of some insects which are not found to secrete it. The yellow substance deposited in vessels containing spiders in alcohol is said to be a true wax, and may be obtained from these animals by gently heating them[668].
ix. Poisons and Acids. The bite as well as the sting of many insects is followed by inflamed tumours, so that the sialisteria of some bugs, Diptera, Aptera and spiders, may be regarded as producing a poisonous fluid; but we know nothing of the real nature of it, nor of that of other venomous insects, except the ant—whose celebrated acid may be considered under the present head,—the bee, the wasp, and the scorpion.
Contrary to the once received doctrine that no acid was to be found in any animal, except as the effect of disease in the alimentary canal, many insects secrete peculiar and powerful ones. I have on a former occasion related an instance in which an acid of this description, secreted in its sialisteria, is employed by a moth to soften its cocoon[669]; and Lister mentions a species of Iulus which produced one resembling that of ants[670]; but this last is the most powerful of all. The fact that blue flowers when thrown into an ant-hill become tinged with red has been long known; but Mr. Fisher of Sheffield, about 1670, seems to have been the first who ascertained that this effect is caused by an acid with which ants abound, and which may be obtained from them by distillation or infusion in water[671]. Margraff and other chemists confirmed this discovery[672]; and concluding that this acid was of a peculiar kind, they gave it the name of the Formic acid. This name, however, is now exploded; the subsequent experiments of Deyeux, Fourcroy and Vauquelin having ascertained that the acid of ants is not of a distinct kind, but a mixture of the Acetic and Malic[673]. These acids are in such considerable quantities, and so concentrated in these animals, that, when a number of Formica rufa are bruised in a mortar, the vapour is so sharp that it is scarcely possible to endure it at a short distance. It also transpires from them, for they leave traces of it on the bodies which they traverse: and hence, according to the experiments of Mr. Coleridge, the vulgar notion that ants cannot pass over a line of chalk is correct; the effervescence produced by the contact of the acid and alkaline being so considerable, as in some degree to burn their legs[674]. The circumstance of much of the food of ants being of a saccharine nature may account for this copious secretion of acid, the use of which is probably to defend themselves and their habitations from the attack and intrusion of their enemies: if a frog be put into a nest of Formica rufa that has been deranged, it will be suffocated in five minutes[675]. That which they ejaculate from their anus when attacked, as formerly stated[676], must be secreted in an ioterium; but their very blood seems of an acid nature. It is very probable, as Dr. Thomson has observed[677], that acids may be obtained from many other insects, and that they are various modifications of the acetic.
From the circumstance that water is absorbed by greasy moths, that crystals of a salt are occasionally found adhering to them, that they change blue litmus paper red,—it has been inferred that their supposed oiliness is in fact an acid or acid salt, having the property of attracting moisture from the air, the infected moths being in fact not greasy, but wet; hence the application of chalk and clay, usually recommended in this case, can have only a temporary and superficial effect. The only effectual remedy, is steeping the body in spirits of wine till all the acid is extracted[678]. This acid is probably the same as Chaussier obtained from silkworms, since called Bombic Acid[679].
The poison of bees and wasps, as to its chemical qualities, is a transparent fluid, at first sweet to the taste, but immediately afterwards hot and acrid like the milky juice of the spurge[680]; soluble in water, but not in alcohol; and separable from the former in the state of white powder, when the latter is added giving a slight red tinge to paper stained with vegetable blue, and when dry and chewed appearing tenacious, gummy and elastic. This last property, as well as solubility in water and not in alcohol, is common also to the poison of the viper, which however differs in being tasteless, and not affecting vegetable blues. From hence Fontana concludes that this fluid is united with an acid, but in a very small proportion, and not with an alkali[681]. The venom of bees is extremely active; a grain in weight, it is conjectured, would kill a pigeon in a few seconds[682]. It is remarkable, however, that while in some constitutions the sting of a single bee or wasp is sufficient sometimes to induce alarming symptoms, in others numerous punctures will produce little or no pain or inflammation. That this fluid, and not the puncture of the sting, is the sole cause of the inflammation that usually follows the wound inflicted by one of these animals, is proved by the facts, that if it be introduced into one made by a needle, the same effect ensues, and that when the whole contents of the poison-bag have been exhausted by the insect's stinging three or four times in succession, its weapon then becomes harmless[683].
The venom of scorpions, though much more potent, probably resembles that of bees, &c., in many of its chemical qualities: it issues from two pores in the sting before described[684], where, when the animal is irritated, it accumulates under the form of two little drops of a whitish colour: spread upon paper this fluid produces a spot like what would be caused by oil or grease, and this part of the paper becomes by desiccation firmer and transparent[685].