More Minor Horrors

Part I

The Governess: And, perhaps, Mabel, as they are not black and as they are not beetles, you will in future call them cockroaches.

Mabel: Certainly, Miss Smith, although they are not cocks and they are not roaches.

(Punch.)

In ‘The Minor Horrors of War,’ we rather neglected the Navy—the senior Service, and till now the more dominant of our two magnificent forces—partly because it is less interfered with by insect pests than is the sister Service, though the common pests of our poor humanity—the flea, the louse, the bug—are, like the poor, ‘always with us.’ Like aeroplanes, insects have captured the air; like motors, they have made a respectable show on land; but they have signally failed at sea. They have nothing corresponding to battleships or submarines; and a certain bug, called Halobates, alone hoists the insect flag on the ocean, and that only in the warmer waters.

Insects are not only highly intelligent animals, but are by far the most numerous and dominant class of the Animal Kingdom; and they have probably come to conclusions about themselves and the sea, comparable to those expressed by Dr. Johnson about man and the ocean: ‘To all the inland inhabitants of every region the sea is only known as an immense diffusion of waters, over which men pass from one country to another, and in which life is frequently lost.’

But one insect at least causes more trouble to sailors than to soldiers—and that is the cockroach. Like the bed-bug, the cockroach came into England at the end of the sixteenth century, and, like the bed-bug, it came from the East. It seems to have been first introduced into England and Holland in the spacious times of Henry VIII by the cross-sea traffic, and from about the end of the sixteenth century the cockroach began gradually to spread throughout the Western world. Like the rat, the bed-bug, and the domestic fly, it has become thoroughly acclimatised to human habitations, and is indeed an associate of man. It is very rarely found living apart from some form or other of human activity.

This insect seems to have been first described in England in Moufet’s ‘Insectorum Theatrum,’ 1634, and he speaks of it as living in flour-mills, wine-cellars, &c., in England, and he tells us how Sir Francis Drake took, in 1584, the San Felipe, a Spanish East Indiaman, laden with spices and burdened with a great multitude of flying cockroaches on board.

This species was Periplaneta orientalis; but there is another and a larger species, which presumably came into England from the West later than its Eastern cousin P. americana—which can frequently be seen in England running about in the cages in our zoological gardens—but it is not on exhibition, it is a by-product, and is not counted in the fee for admission to the gardens.

Latter tells us there are ten species of Blattodea which occur in Britain; but only three of these are indigenous, and these three all belong to the genus Ectobia. Ectobias are smaller than cockroaches, and do not frequent human habitations, but live in shrubs, under rubbish heaps, &c. Some species of Ectobia are, however, very destructive and have been known to destroy in one day the whole accumulation of dried but not properly salted fish in a Lapland village. Of the remaining species of cockroach most are local, and occur sporadically in particular factories, or places where food is stored but they are not very widely spread.

As we have said above, P. orientalis is the common English cockroach, P. americana occurs especially in zoological gardens and menageries; but a third species, P. germanica, sometimes gets established. Mercifully, P. germanica does not seem to spread. Neither P. germanica nor P. americana seem to make much headway against P. orientalis, which appears to be predominant over both these other species.

P. germanica is probably most methodical, very thorough, very brave, very faithful—but rather lacking in the power of understanding the point of view of others. If it has any association with its specific name, it illustrates the most striking example in the world’s history of the divorce of wisdom from learning. ‘O Lord! give us understanding,’ should be the prayer of P. germanica.

Miall and Denny tell us that from the first introduction of P. orientalis into England it took two centuries before it spread far beyond London. In 1790 Gilbert White speaks of it as ‘an unusual insect, which he had never observed in his house till lately,’ and, indeed, at the present moment many English villages are still blissfully ignorant of this particular nuisance.

As Fig. 2 shows, the cockroach is a somewhat slackly put together insect. One might almost call it rather slatternly and loose-jointed—and the latter it certainly is. Its head moves freely on the thorax, and the thorax on the abdomen. The successive segments of the latter move very freely on one another. The legs are long and mobile, and so are the antennae with which the animal is ceaselessly testing the ground over which it flits hither and thither in its restless activity.

Cockroaches are very difficult to catch. They practically never walk, but run with a hardly believable rapidity, darting to and fro in an apparently erratic mode of progression. Even when caught they are not easily retained, for they have all the slipperiness of a highly polished billiard-ball. They have great powers of flattening their bodies, and they slip out of one’s hand with an amazing dexterity. Besides their slipperiness they have another weapon, and that is a wholly unpleasant and most intolerable odour, which is due to the secretion of a couple of glands situated on the back of the abdomen. The glands which produce this repellent odour are sunk in the soft membrane which unites the fifth and sixth abdominal segments, and the moment a cockroach is attacked it exudes a sticky, glue-like fluid, which gives out this most unendurable smell. The fluid is extraordinarily tenacious and difficult to remove from the hand of those who have touched the insects. No doubt the cockroach, in nature, finds safety in this from the attacks of insectivorous animals.

Cockroaches, as has been said, very rarely walk, they nearly always run, and they advance the first and third leg of one side at the same time as the middle leg of the other, pulling themselves forward with their front legs and pushing themselves forward with the hindermost. They are thus constantly poised on a tripod. They occasionally, but not very often, use their wings for flight. When they do so, their anterior wings are stretched out at right angles to the body, and take no active share in beating the air. They act in effect as monoplanes. It is the hinder wings which really do the active flying. After a flight, the hinder wings are shut up something in the manner of a fan.

The flattened coxae, or thighs, of the leg are adapted for shovelling débris back from beneath the body when the insect is enlarging its habitation. When the cockroach gets into a dusty ‘milieu’ the dust is immediately removed; the hairs on the legs act as clothes-brushes and brush every part of the body, whilst the antennae, which attract any dust in the neighbourhood, are repeatedly drawn through the closed mandibles and so cleaned. A cockroach is able to walk on smooth surfaces because it possesses between the joints of the tarsus certain soft, white patches, very velvety, and these give the creature a good hold, and prevent slipping even on glass.

Cockroaches will eat pretty well everything. They are a great nuisance on board ship, where they are said to gnaw the skin and nibble the toe-nails of sailors. Hardly any animal or vegetable substance is absent from their menu. It is said that they will even devour bed-bugs, and that natives on the African shores, troubled by these semi-parasites, will beg cockroaches as a favour from sailors in passing ships.

The mandible (Fig. 3), with its strongly toothed surface, is capable of biting and grinding into fragments a very varied diet. The food is moistened by the secretion of the salivary glands, which is capable of converting starch into the more soluble sugar. The food is further ground up by a series of hard ridges projecting into the inner face of the gizzard (Fig. 4, 7). The secretion of the so-called hepatic caeca is capable of emulsifying fat and rendering proteins soluble. Thus the ordinary food substances are reduced to a condition in which they are capable of diffusing from the lumen of the alimentary canal into the blood which floods the body cavity.

The external movement—one might almost say ‘the panting’—which is very obvious in the abdomen, the alternate flattening and deepening of this part of the body, is a movement of inspiration and expiration, the air being driven into the stigmata and so into the tracheae or breathing-tubes. There is a considerable variation in the rate of these pulsations, but the cockroach’s heart beats at an average rate of seventy to eighty contractions per minute.

Although cockroaches have fairly developed eyes, they seem to trust very largely to tactile impressions in appreciating their relations to the surrounding world. Their antennae and the palps of their first and second maxillae are constantly touching the surface on which they are resting or moving, and from time to time their antennae wildly wave in the air in a manner which suggests that they are smelling out the external circumstances which environ them. The 39,000 sensory ‘nerve-endings’ which are found in the antennae of the male cockroach are almost certainly olfactory in function. At the posterior end of the body the two ‘cerci’ are also sensitive to tactile impressions, and probably act at the hinder end of the cockroach as the antennae act at the forward end. Cockroaches are certainly keenly sensitive to light, and, as every one knows, they shun the light, and when detected in daylight or candle-light they make as quickly as they can for some dark hole or crevice in which to hide.

Cockroaches breed during the summer, and their eggs are laid in packets of sixteen in a capsule or cocoon with rounded ends, and with an upper corrugated edge. These cocoons are very like the little hand-bags ladies have carried since the dressmakers denied them pockets. There are sixteen ovarian tubes in the female, and each of these deposits one egg in each cocoon. The ventral portion of the seventh abdominal segment in the female is shaped like the prow of a boat, and it is in this structure that the cocoon, or egg-case, is built up. Each egg is fertilised by a spermatozoon which has been deposited by the male in the spermatheca of the female. The eggs are placed in a double row, eight in each row, facing each other, and, as they gradually develop, it becomes apparent that the ventral face of one row faces the ventral face of the other row—just as the little choir-boys on the Gospel side of a chancel face the little choir-boys on the Epistle side, but much nearer together—and that their heads are all directed towards the corrugated ridge.

They are at first quite white, but with large black eyes, and it has often struck me how surprised they must be when they awake to consciousness and find themselves staring at a brother or sister cockroach just opposite, of whom they have had hitherto no consciousness. The ripe embryos secrete some fluid, probably saliva, which dissolves the ridge, and it is through this dissolved or softened ridge that they ultimately make their way into the outer world.

Young cockroaches are very active, running about and seeking everywhere for any food of a starchy nature. They are, in fact, miniatures of their parents, for a cockroach, like many of the primitive insects, has a direct development, and there are no such stages as caterpillar and pupa in their life-history.

But, like other insects, cockroaches change their skin from time to time, and they lose little time before beginning this ecdysis, for they first cast their cuticle immediately after escaping from the egg-capsule. The second ecdysis is four weeks later, and the third at the end of the first year, and after this time they moult annually. At the seventh moult, when the animal is now four years old, it assumes the form of the perfect insect, and is capable of reproduction. The later moults fall in the summer time, and so does fertilisation and oviposition. Male cockroaches may be distinguished from the females by their well-developed wings and wing-covers. They stand higher on their legs than do the females, whose abdomens often trail upon the ground.

In spite of the noxious secretion of their abdominal glands there are creatures who habitually feed on cockroaches—hedgehogs, for instance, are frequently imported into our houses to check these pests. Rats, cats, polecats, frogs, and wasps have been known to eat them, and some few of the digging-wasps lay them down in their larders for the use of their progeny. Some birds will also tackle them. But even the most devoted friend of cockroaches can find little to say in their favour, except that they are currently reported to form the basis of the flavouring of a very popular sauce; but even wild cockroaches will not drag from me what the name of that particular sauce is.