The Natural History of the Cockroach.

Range.

The common Cockroach is native to tropical Asia,14 and long ago made its way by the old trade-routes to the Mediterranean countries. At the end of the sixteenth century it appears to have got access to England and Holland, and has gradually spread thence to every part of the world.

Perhaps the first mention of this insect in zoological literature occurs in Moufet’s Insectorum Theatrum (1634), where he speaks of the BlattÆ as occurring in wine cellars, flour mills, &c., in England. It is hard to determine in all cases of what insects he is speaking, since one of his rude woodcuts of a “Blatta” is plainly Blaps mortisaga; another is, however, recognisable as the female of P. orientalis; a third, more doubtfully, as the male of the same species. He tells how Sir Francis Drake took the ship “Philip,”15 laden with spices, and found a great multitude of winged BlattÆ on board, “which were a little larger, softer, and darker than ours.” Perhaps these belonged to the American species, but the description is obscure. Swammerdam also was acquainted with our Cockroach as an inhabitant of Holland early in the seventeenth century. He speaks of it as “insectum illud Indicum, sub nomine Kakkerlak satis notum,” and very properly distinguishes from it “the species of ScarabÆus” (Blaps), which Moufet had taken for a Blatta.16

The American Cockroach is native to tropical America, but has now become widely spread by commerce. An Australian species also (P. australasiÆ) has begun to extend its native limits, having been observed in Sweden,17 Belgium, Madeira, the East and West Indies,18 Florida,19 &c. In Florida it is said to be the torment of housekeepers.

To the genus Blatta belong a number of small European species, which mostly lurk in woods and thickets. Some of these are found in the south of England. B. lapponica is one of the commonest and most widely distributed. It is smaller than the common Cockroach, and both sexes have long wings and wing-cases. The males are black and the females yellow. It is found on the mountains of Norway and Switzerland as high as shrubs extend, and when sheltered by human dwellings, can endure the extreme cold of the most northern parts of Europe. This is the insect of which LinnÆus tells, that in company with Silpha lapponica it has been known to devour in one day the whole stock of dried but unsalted fish of a Lapland village. B. germanica also has the wings and wing-cases well developed in both sexes. Two longitudinal stripes on the pronotum, or first dorsal plate of the thorax, are the readiest mark of this species, which is smaller and lighter in colour than the common Cockroach. It is plentiful in most German towns, and has been introduced from Germany into many other countries;20 but it appears to be native, not to Germany alone, but to Asia and all parts of central and southern Europe. Where and how it first became domesticated we do not know.

The other species of Cockroaches which have been met with in Europe are Panchlora maderÆ, said by Stephens to be occasionally seen in London, and Blabera gigantea the Drummer of the West Indies, which has often been found alive in ships in the London Docks.

Blatta germanica, Periplaneta orientalis, and P. americana, are so similar in habits and mode of life as to be interchangeable, and each is known to maintain itself in particular houses or towns within the territory of another species, though usually without spreading.

Orientalis is, for example, the common Cockroach of England, but germanica frequently gets a settlement and remains long in the same quarters. H.C.R., in Science-Gossip for 1868, p.15, speaks of it as swarming in an hotel near Covent Garden, where it can be traced back as far as 1857. In Leeds, one baker’s shop is infested by this species; it is believed to have been brought by soldiers to the barracks, after the Crimean war, and to have been carried to the baker’s in bread-baskets. We have met with no instance in which it has continued to gain ground at the expense of orientalis. Americana also seems well established in particular houses or districts in England. H.C.R. (loc. cit.) mentions warehouses near the Thames, Red Lion and Bloomsbury Squares, and the Zoological Gardens, Regent’s Park. It frequents one single warehouse in Bradford, and is similarly local in other towns with foreign trade.

Many cases are recorded in which germanica has been replaced by orientalis, as in parts of Russia and Western Germany, but detailed and authenticated accounts are still desired. On the whole orientalis seems to be dominant over both germanica and americana.

The slow spread of the Cockroaches in Europe is noteworthy, not as exceptional among invading species, but as one more illustration of the length of time requisite for changes of the equilibrium of nature. It took two centuries from the first introduction of orientalis into England for it to spread far from London. Gilbert White, writing, as it would appear, at some date before 1790, speaks of the appearance of “an unusual insect,” which proved to be the Cockroach, at Selborne, and says: “How long they have abounded in England I cannot say; but have never observed them in my house till lately.”21 It is probable that many English villages are still clear of the pest. The House Cricket, which the Cockroaches seem destined to supplant, still dwells in our houses, often side by side with its rival, sharing the same warm crannies, and the same food. The other imported species, though there is reason to suppose that they cannot permanently withstand orientalis, are by no means beaten out of the field; they retreat slowly where they retreat at all, and display inferiority chiefly in this, that in countries where both are found, they do not spread, while their competitor does. It may yet require some centuries to settle the petty wars of the Cockroaches.

It is also worth notice that in this, as in most other cases, the causes of such dominance over the rest as one species enjoys are very hard to discover. We cannot explain what peculiarities enable Cockroaches to invade ground thoroughly occupied by the House Cricket, an insect of quite similar mode of life: and it is equally hard to account for the superiority of orientalis over the other species. It is neither the largest nor the smallest; it is not perceptibly more prolific, or more voracious, or fonder of warmth, or swifter than its rivals, nor is it easy to see how the one conspicuous structural difference—viz., the rudimentary state of the wings of the female, can greatly favour orientalis. Some slight advantage seems to lie in characteristics too subtle for our detection or comprehension.

Food and Habits.

As to the food of Cockroaches, we can hardly except any animal or vegetable substance from the long list of their depredations. Bark, leaves, the pith of living cycads, paper, woollen clothes, sugar, cheese, bread, blacking, oil, lemons, ink, flesh, fish, leather, the dead bodies of other Cockroaches, their own cast skins and empty egg-capsules, all are greedily consumed. Cucumber, too, they will eat, though it disagrees with them horribly.

In the matter of temperature they are less easy to please. They are extremely fond of warmth, lurking in nooks near the oven, and abounding in bakehouses, distilleries, and all kinds of factories which provide a steady heat together with a supply of something eatable. Cold is the only check, and an unwarmed room during an English winter is more than they can endure. They are strictly nocturnal, and shun the light, although when long unmolested they become bolder. The flattened body enables the Cockroach to creep into very narrow crevices, and during cold weather it takes refuge beneath the flags of a kitchen floor, or in other very confined spaces.

The Cockroach belongs to a miscellaneous group of animals, which may be described as in various degrees parasitic upon men. These are all in a vague sense domestic species, but have not, like the ox, sheep, goat, or pig, been forcibly reduced to servitude; they have rather attached themselves to man in various degrees of intimacy. The dog has slowly won his place as our companion; the cat is tolerated and even caressed, but her attachment is to the dwelling and not to us; the jackal and rat are scavengers and thieves; the weasel, jackdaw, and magpie are wild species which show a slight preference for the neighbourhood of man. All of these, except the cat, which holds a very peculiar place, possess in a considerable degree qualities which bring success in the great competitive examination. They are not eminently specialised, their diet is mixed, their range as natural species is wide. Apart from man, they would have become numerous and strong, but those qualities which fit them so well to shift for themselves, have had full play in the dwellings of a wealthy and careless host. Of these domestic parasites at least two are insects, the House-fly and the Cockroach; and the Cockroach in particular is eminent in its peculiar sphere of activity. The successful competition of Cockroaches with other insects under natural conditions is sufficiently proved by the fact that about nine hundred species have already been described,22 while their rapid multiplication and almost worldwide dissemination in the dwellings of man is an equally striking proof of their versatility and readiness to adapt themselves to artificial circumstances. In numerical frequency they probably exceed all domestic animals of larger size, while in geographical range the five species, lapponica, germanica, orientalis, americana, and australasiÆ, are together comparable to the dog or pig, which have been multiplied and transported by man for his own purposes, and which cover the habitable globe.

The Cockroach a persistent type.

The Cockroach is historically one of the most ancient, and structurally one of the most primitive, of our surviving insects. Its immense antiquity is shown by the fact that so many Cockroaches have been found in the Coal Measures, where about eighty species have been met with. The absence of well-defined stages of growth, such as the soft-bodied larva or inactive pupa, the little specialised wings and jaws, the simple structure of the thorax, the jointed appendages carried on the end of the abdomen, and the unconcentrated nervous system, are marks of the most primitive insect-types. The order Orthoptera is undeniably the least specialised among winged insects at least, and within this order none are more simple in structure, or reach farther back in the geological record than the Cockroaches. The wingless Thysanura are even more generalised, but their geological history is illegible.23

Life-History.

The eggs of the Cockroach are laid sixteen together in a large horny capsule. This capsule is oval, with roundish ends, and has a longitudinal serrated ridge, which is uppermost while in position within the body of the female. The capsule is formed by the secretion of a “colleterial” gland, poured out upon the inner surface of a chamber (vulva) into which the oviducts lead. The secretion is at first fluid and white, but hardens and turns brown on exposure to the air. In this way a sort of mould of the vulva is formed, which is hollow, and opens forwards towards the outlet of the common oviduct. Eggs are now passed one by one into the capsule; and as it becomes full, its length is gradually increased by fresh additions, while the first-formed portion begins to protrude from the body of the female. When sixteen eggs have descended, the capsule is closed in front, and after an interval of seven or eight days, is dropped in a warm and sheltered crevice. In Periplaneta orientalis it measures about ·45in. by ·25in. (fig.5). The ova develop within the capsule, and when ready to escape are of elongate-oval shape, resembling mummies in their wrappings. Eight embryos in one row face eight others on the opposite side, being alternated for close packing. Their ventral surfaces, which are afterwards turned towards the ground, are opposed, and their rounded dorsal surfaces are turned towards the wall of capsule; their heads are all directed towards the serrated edge. The ripe embryos are said by Westwood to discharge a fluid (saliva?) which softens the cement along the dorsal edge, and enables them to escape from their prison. In Blatta germanica the female is believed to help in the process of extrication.24 The larvÆ are at first white, with black eyes, but soon darken. They run about with great activity, feeding upon any starchy food which they can find.

Fig. 5.—Egg-capsule of P. orientalis (magnified). A, external view; B, opened; C, end view.