The cockroaches are remarkable for the excessive rapidity with which they run, or rather scurry, their gait being very peculiar. The common domestic forms, when alarmed, disappear with great agility, seeking obscure corners in which to hide themselves, it being part of their instinct to flee from light. Hence they are called lucifugous, and are most of them entirely nocturnal in their activities. In the South of Europe and other warmer regions many Blattidae may, however, be found on bushes and foliage in the daytime; these, when alarmed, fall down and run off with such speed and in so tortuous a manner, that it is a very difficult matter to seize them. It is recorded that the males of the genus Heterogamia are attracted by lights, though their apterous females keep themselves concealed underground in sandy places.
We may take this opportunity of alluding to the attraction that light exerts on Insects. Many species that conceal themselves during the daytime and shun light as if it were disagreeable, are at night-time so fascinated by it that it is the cause of their destruction. The quantity of Insects killed in this way by electric and other bright lights is now enormous; in many species the individuals immolate themselves by myriads. It would appear that only nocturnal and winged species are so attracted. So far as we know, light has no fascination for Insects except when they are on the wing. The phenomenon is not understood at present.
The food of Blattidae is believed to be of a very mixed character, though Brunner considers that dead animal matter is the natural nutriment of the members of this family. It is well known that the common cockroach eats a variety of peculiar substances; its individuals undoubtedly have the somewhat too economical habit of eating their own cast skins and empty egg-capsules, but in this they only act like many other much admired Insects. S. orientalis is gregarious, and the individuals are very amicable with one another; small specimens sit on, or run over the big individuals, and even nestle under them without their displaying the least resentment. The common cockroach is a rather amusing pet, as the creatures occasionally assume most comical attitudes, especially when cleaning their limbs; this they do somewhat after the fashion of cats, extending the head as far as they can in the desired direction, and then passing a leg or antenna through the mouth; or they comb other parts of the body with the spines on the legs, sometimes twisting and distorting themselves considerably in order to reach some not very accessible part of the body.
There is very little information extant as to the domestic Blattidae found in parts of the world outside Europe, but it seems that there are numerous species that prefer the dwellings of man, even though they only tolerate the owners. Belt says[[159]] "the cockroaches that infest the houses of the tropics are very wary, as they have numerous enemies—birds, rats, scorpions, and spiders; their long trembling antennae are ever stretched out, vibrating as if feeling the very texture of the air around them; and their long legs quickly take them out of danger. Sometimes I tried to chase one of them up to a corner where on a wall a large cockroach-eating spider stood motionless looking out for his prey; the cockroach would rush away from me in the greatest fear, but as soon as it came within a foot of its mortal foe nothing would force it onwards, but back it would double, facing all the danger from me rather than advance nearer to its natural enemy." To this we may add that cockroaches are the natural prey of the fossorial Hymenoptera of the group Ampulicides, and that these wasps sometimes enter houses in search of the Insects.
Fig. 127.—Nocticola simoni. A, male; A1, tegmen and rudiment of wing; A2, front of head; B, female. The cerci are broken, in B the right one is restored in outline. (After Bolivar.)
We have already noticed the considerable difference that exists in many cases between the sexes of the same species. This is sometimes carried to such an extent that nothing but direct observation could make us believe that the males and females are of one kin. Fig. 118 (p. [220]) shows a case of this kind. Though the young as a rule are excessively similar to the adults, yet this is by no means invariably the case. In some of the more amply winged forms, such as Blabera, the young is about as different from the adult as the female of Heterogamia is from its male. In Blattidae it is always the case—so far as is yet known—that when there is a difference as regards the alar organs between the two sexes, it is the male that has these structures most developed, and this even when they can be of little or no use for purposes of flight.
Among the most interesting forms of the family are the two species of the genus Nocticola, recently discovered by M. Simon in caves in the Philippine Islands.[[160]] They are amongst the smallest of the Orthoptera, the male being scarcely ⅛ of an inch long. In the larval state of N. simoni the ocular organs exist as three ocelli, or facets, on each side of the head, and in the perfect state the number is increased somewhat, as shown in Fig. 127, A2. In the second species of the genus the female is quite blind (the male being still undiscovered). The fenestræ in Nocticola are absent; the tegmina and wings are totally wanting in the female (Fig. 127, B), but are present in a very peculiar condition in the male (Fig. 127, A1). There are other anomalies in the structure of these cavernicolous Insects, the cerci being apparently of peculiar structure, and the spines of the legs more hair-like than usual. The condition of the eyes is remarkable; the peculiarity in their development is worthy of study.
Fig. 128.—Corydia petiveriana, with tegmina extended, A; closed, B.