The Parents' Review

A Monthly Magazine of Home-Training and Culture

Defence in the Insect World

[Alfred Thornley, 1855-1947, "studied at Oxford, took holy orders and worked as deacon and priest at parishes in Nottinghamshire. He had a wide interest in natural history, but specialized in entomology and the study of Diptera. He was relieved of most of his parochial duties, and worked with the County Education Department in training school teachers in natural history. Thornley was Chaplain and Professor of Economic Entomology at Cirencester Agricultural College for three years, before retiring to Cornwall. Thornley gave his collections, journals and notebooks to The Natural History Museum in 1946." Source]

I remember a few years ago, gazing at what was a veritable little garden on top of a limestone wall in Somersetshire. It was all contained on a small block of stone. There was an azure blue mass of early field Speedwell (Myosotis Collina) elbowed out by a pushing clump of rue-leaved Sacrifrage (Sax. Tridactylites). In and out grew clumps of Cetarach Fern, and several patches of moss. Now the whole of the soil out of which these plants grew might have been put into an egg cup. As I looked at this I realized more fully than ever before, the meaning of that pregnant phrase, 'the struggle for existence.' I wondered how many other seeds had fallen on that scanty shallow bit of soil; how many had died, had been quite unable to fight out the battle of life amidst so many competitors. I thought of the wonderful hardy constitution of these plants, which had been able to survive all these hard conditions of growth. My thoughts next passed to the immense world of insects; the vast hosts of flies, beetles, moths, butterflies, bees, ants, bugs, etc. and I felt what an awfully keen struggle for existence must be here. A study of the order soon convinces one that this is the case. Insects abound in special means of defence and protection, as also in possessing almost every conceivable weapon of attack. Not only the sword and spear of primitive warfare, but even the resources of modern artillery, have been found utilized in the insect world. It is said that cannon was employed for the first time by King Edward III against the Scots in 1327, but a small beetle, fitly called the 'Bombardier' (Brachinus Crepitans) carries its powder and shot with it. Woe to the large tyrant that presses it too hotly in pursuit, for in a moment there is a report, followed by a little cloud of blue smoke, and the pursuer returns sadly on his homeward way, probably with incipient opthalmia of a virulent type threatening to darken his life for some time. The subject of Insect Defence is not only exceedingly interesting, but one to which almost any one of sufficient observing ability may make valuable contributions, as the habits of some of the very commonest of insects have scarcely been studied as well as they might be. It is usual to consider the subject under the heads of 'passive and active means of defence.' Nor need I say much now under the first head. In a former paper on Mimicry I have already said a good deal on the passive mode of protection to which so many insects owe their preservation. Yet has it ever struck you that many races of insects are preserved through the excessive numbers in which they are produced? It being just a simple impossibility to kill them all off in a single season, or within the active lifetime of their enemies. And insects which adopt this mode of preserving their species are always more or less of a weak and fragile build, or possess means of defence so feeble as to be quite inadequate to their preservation.

This case may be illustrated by the Aphides, or "Green fly," of our gardens and conservatories. To all eating nature round about, a fat and succulent aphis must be a bonne bouche, and a constant demand for dinners of this kind ad lib, must necessitate an enormous supply being kept up. Yet nature is quite equal to this strain on her resources, for in order to furnish this supply she has recourse to a mode of reproduction in the aphis, subsidiary to her ordinary method. Provided that temperature is high enough, the aphides are able to reproduce "asexually," that is without the aid of any males, sometimes for eight or nine generations continuously, yet towards the end of summer true males and females are produced, and eggs are laid in the chinks and crevices of the barks of trees, or at the roots of plants, which develop in the first warm days of the following spring. There is perhaps no more interesting chapter of natural history, than that which relates the habits of the aphis.

The next great principle of passive defence would come under a head, which has already been discussed in a former paper in this magazine, namely, Imitation or Mimicry. In this form of protection nature saves in energy. There is one side of it still much under discussion, and to which I will draw your attention again. Many male insects, as well as some females, possess greatly developed horns or appendages on the head or thorax chiefly, suggesting very active powers of combat. Yet in the case of numerous species of which the life history is best known, these singular weapons seem never to be put to any warlike use, and indeed seem often to us, too much out of all proportion to be of any real service, and more likely to be of the nature of a hindrance than a use. It then becomes an interesting question, what is the use of this singular armour? The species which have been studied for the most part are vegetable feeders, quiet and inoffensive in their habits and slow in their movements. May they not be entirely ornamental, the result of sexual selection; being analogous to the beautiful plumage, crests, ocelli, hackles, &c., of many male birds; a result of the action of the same class of instincts which urge a dusky warrior to dress himself in such grotesque and gruesome fashion, partly to strike fear into the hearts of his enemies, and partly to look "big" in the eyes of the maidens of his tribe. I have before me now a monster of a beetle from China. It has proceeding from its head, which is proportionately very small, a huge horn quite an inch long. Near the apex this organ is divided into two short branches, each of which is again split into two. Not content with this pitch-fork arrangement, the creature has developed from its thorax a much smaller, but quite as evil-looking a horn, which is also forked at its extremity. Yet all this frightful apparatus is probably a farce! The species is a quiet, slow-crawling, small-mouthed vegetarian, Lamellicorn. But I notice one thing, that when he gets his head down low, as he would in repose, then the two horns simulate the appearance of a frightful pair of jaws, the very sight of which must strike terror into his foes. Yes, there is no doubt he is a "Bogey Man" in the beetle world.

But I must pass over all those various ways in which insects protect themselves by imitating seeds or leaves, or twigs, or by approximating in colour to that of their environment, and go on to mention a few of the more or less active ways in which these interesting creatures preserve their existence. And the first mode which I shall mention is by the secretion of evil smelling or coloured fluids, sometimes of a highly corrosive nature. In fact they are the "Skunks" of the Insect World. I remember a few years ago I was in Norwegian Lapland, and being at that time rather keen on anthropological and archaeological subjects, thought I should like to investigate the internal arrangements of one of those beehive kind of huts in which the Laps dwell. I tried to effect an entrance, but the "ancient fish-like smell," which pervaded the whole establishment, drove me back to the more generous supply of oxygen outside. I have always thought since then, that the production of an evil smell is not at all a bad means of defence. I think, probably, many of my readers have very much discovered this for themselves in the case of beetles. Most of the rapidly running ground beetles produce a vile smelling fluid from their mouths if handled. Some of my readers must have found, occasionally, in cellars and old churches, a black, funereal-looking beetle, taking about ten seconds to lift each leg as it crawls slowly along the floor or up the wall. This is the "Sexton" or Churchyard Beetle (Blaps Mortisaga). But, oh! my fair readers, as you value your white hands, and the society of your friends, don't, please don't, touch it! It will infect you with a gentle aroma of mixed coffins and assafoetida! [assafoetida is a strong spice with a pungent smell, often used in Indian cuisine] and it will be a long time before you get rid of it. There is such a very comical description of this ill-favoured creature in an old book, [Thomas] Moufet's Theatre of Insects, published in London in 1634, that I cannot refrain from extracting it. "It hath thin slender long shanks; remains in deep cellars; it creepeth very slowly, but at the least glimpse of light and whisper of talk, she hides herself; a shamefac't creature certainly, and most impatient of light, not so much for its ill-favouredness, but the guiltiness of its conscience in regard of the stinke it leaves behind it, and of its ill-behaviour, for it frequents base places, and digs through men's wals, and doth not only annoy those that stand near it, but offends all the place thereabouts with its filthy savour." Against this unsavoury description we ought in justice add, that the same writer recommends the beetle as a certain cure for earache, if beaten up with "old wine, honey, pomegranate rind, unguentem Syriacum apple juice, tar and onion," this grateful and soothing, though somewhat complicated compound, was to be poured into the ear, when cold. My readers will gather from this that entomology has made a little progress since the days when quaint old Moufet lived.

A more singular mode of protection is practised by a few beetles. The moment you touch them, or in any way intercept their progress, they cause to exude from their bodies a plentiful supply of a highly coloured oily substance. In case of a large blue-black species, found quite commonly on low herbage in spring and summer (Timarcha Laevigata), so copious is this secretion and so ruddy, as to obtain for the creature the somewhat unpleasant name of the "bloody nosed beetle." Now it does not appear from such analysis as has been made of this singular secretion, that it is poisonous, so that it must act as a means of defence rather from the side of its disagreeableness. The 'oil beetles,' found so commonly in early spring clustering about the celandine leaves on sunny banks, are I think well known, and no one will deny that the oily secretion must deter their foes from molesting them, for they are most conspicuous and soft insects, with a large amount of abdomen, a very dainty morsel to a bird; yet they are commonly abundant and found in numbers together. I hope in the future, now that the secret is out, none of my readers will be afraid of taking up any of these singular creatures and examining them. The oil has no unpleasant smell, and a little soap and water soon removes it from the fingers. Whilst we are on this subject of protective secretions I might call your attention to another common and interesting case, namely, that of the 'Cuckoo-spit' or frog hopper. Every one must have noticed that spittle-like secretion on the stems of plants and flowers. This is caused by a little creature belonging to a large division of the 'Bug family'--the Homoptera, and is closely allied in its structure to the classical 'Cicada.' It is the larva only which makes the frothy secretion referred to; in its perfect condition it is the pretty little frog hopper so abundant during summer in our gardens and everywhere. The little creature which perches on your coat, and for some time you are not sure which is its head and which is its tail; but when you touch it, it gives a tremendous jump, clearing nearly a yard at a time. We can well imagine that this soft and tender little animal does derive some protection from its moist environment; first in a way of concealment, and then from its suggestive disagreeableness; nevertheless that tyrant, the wasp, has been seen to pull the little creatures out of their frothy homes and devour them. Now all these creatures mentioned protect themselves, if in a disagreeable manner, yet with some sense of decency, but I am most ashamed to tell you to what disgusting lengths some creatures go. There is a shame-faced genus of beetles, with a few first cousins also, who go the length when they are in the larval condition, of covering themselves entirely over with their own excrement. The larvae of the pretty little green tortoise beetles, found so commonly on ragworts by the sea shore, do this, and if you have a scientific mind you may pass an hour not unprofitably in learning how they do it. For these little creatures have solved in a marvelous manner some rather difficult mechanical problems. The larva of the beautiful lace-winged fly (Chrysopa) feeds upon the innumerable hosts of Aphides, and makes itself a coat out of the slain innocents.

There is also a bug, (Reduvius Personatus), which would be disgusting, if it were not the sworn foe of that imported plague of ours, the "B flat." [B flat - bedbug] This latter pest is said to have come into the country about the beginning of the sixteenth century. However the larva of the Reduvius makes short work of him: and to effect this quickly and successfully, he clothes himself with a garment of dust and dirt, till you cannot tell he is a creature at all. About him the hosts of B flats swarm, thinking him a gem in the way of dirt and filth, meanwhile he quietly annexes first one and then another, till a considerable inroad is made in the flock. He haunts just the same dirty corners that they do, and I am afraid is often killed by anxious housewives in mistake; for the cure certainly seems too much like keeping a tiger to keep down the mice. But if I were to go on detailing some of the more horrible ways in which insects protect themselves, I am sure you would abjure Entomology altogether, and as my duty is to attract you to the subject, I must now pass on to some of the pleasanter ways in which these small and delicate creatures preserve themselves.

That insects fight and engage in deadly combats everyone knows, and that for this purpose the jaws are greatly developed and armed with teeth. Perhaps of all insects the Ants are at once the most pugnacious, and the most orderly in their warfare. So interesting indeed are they in all their habits, that it would be quite impossible to say much in a short and general paper like this. But it may be remarked under the head of offensive means of protection, that some species of Ants sally out in an orderly manner to attack another species; nor does the matter end with a battle royal, but the conquerors carry away deliberately a certain number of the conquered and make slaves of them. Nor do these prisoners show any unhappiness in their captivity, but diligently apply themselves to the care of the young larvae and pupae, and feed and clean their conquerors. Nay even, as Sir John Lubbock tells us, the very life of the conquerors seems sometimes to depend on these slaves, for so degenerate have they become in some ways, that they cannot even feed and clean themselves. This is certainly most extraordinary, and would scarcely be believed if the testimony of many and accurate observers did not go to corroborate the statements. Only in last week's Nature, I read of the interesting discovery, that some kinds of South American Ants, deliberately cultivate a species of Fungus in their nests, that they may never be in want of food, and the description of these Fungus gardens is of the most absorbing interest. I have already referred at the commencement of this paper to the remarkable way in which some beetles protect themselves, by ejecting from the extremity of their bodies an explosive fluid, which becomes gaseous in contact with the air. This is probably formic acid, which occurs in the stings of many insects, as well as in that of the nettle. The little "Bombardier" beetle, common in the South of England, is however represented by quite large species in South America, whose artillery is really of a dangerous kind. The Pherosophus Complanatus, for example, a large South American species, of which we read that when it is caught "will often crepitate [make a cracking sound] quite loudly several times in succession, and cause a burning sensation in the fingers, which are stained brown where the vapour has touched them."

Again many insects produce curious noises, squeakings, clicks, stridulations, but whether these noises are of use as a means of defence it is not always easy to say. The Ageronia Feronia, a South American butterfly, is said by Mr. Darwin, to make a noise "like a toothed wheel passing under a spring catch," which could be heard at a distance of several yards. Some of our own beautiful butterflies, the "Peacock" and "Red Admiral" and "Purple Emperor" have been reported to produce slight noises, and some of my readers may perhaps be able to confirm this statement from their own observations, and say what is the particular purpose of it. The well known "Death's Head Hawk Moth" (Acherontia Atropos) makes a loud squeaking noise at times; and as he is a great thief, and steals honey of the poor bees, he has been supposed to strike terror into them by this noise; but whether so or not, he frequently gets the worst of it, as the following instance, reported in the Entomologist's Monthly Magazine for September, would seem to show. The moth "was covered with bees, which were pushing it out at the entrance, and endeavouring to kill it. Apparently it had been stung, for it seemed unable to fly, yet made a loud squeaking noise as if in self defence." To this the editors append an interesting note: "It sometimes happens that the bees cannot eject the intruder, and dispose of its body by entombing it in wax."

It will be scarcely necessary to do more than remind you that innumerable species of insects are protected by the possession of stings, or a very formidable biting apparatus. The sting, which is sometimes the exclusive possession of the female, has been proved to be nothing but a modified ovipositor. Yet it is a terrible weapon of offence and defence. Already this year two deaths from the sting of a wasp have been reported, one of which, sad to relate, occurred in my own village, and caused death in about twenty minutes. The sting of the hornet is even more to be dreaded, and we are not surprised at the threat of the Almighty, to drive out the heathen nations of Canaan by means of this insect.

I think I have now compassed pretty well all the more interesting methods of defence amongst insects, and I hope I have shown you what a great deal there is yet to learn on this subject, and indicated to you certain lines along which profitable investigation may be conducted. It only remains for me to say now, that I will answer or endeavour to answer any queries relative to insect life which may be put to me, and that it will give me great pleasure to do so.

Proofread by LNL, June, 2023