236 ORTHOPTERA 



There is very little evidence on which to base an estimate 

 of the number of species of Blattidae existing in the world at 

 present. Probably the number extant in collections may amount 

 to 1000 or thereabouts, and the total existing in the world may 

 be as many as 5000. The species of Blattidae cannot tolerate 

 cold, and are consequently only numerous in tropical regions. 

 Europe possesses about twenty species, and in Britain there are only 

 three that are truly native ; these are all small Insects belonging 

 to the genus JEJctohia, said living out of doors, amongst leaves, 

 under bushes, and in various other places. We have, however, 

 several other species that have been introduced by the agency of 

 man, and these all live under cover, where there is artificial warmth 

 and they are protected from the inclemencies of the winter season. 

 The commonest of these forms is Stylopyga orientalis, the " black 

 beetle " of our kitchens and bakehouses. This Insect is said to 

 have been brought to Europe from " Asia " about 200 years ago, 

 but the evidence as to its introduction, and as to the country of 

 which it is really a native, is very slight. It is indeed said ^ that 

 S. orientalis has been found in peat in Schleswig-Holstein. Peri- 

 planeta americana is a larger Insect, and is common in some 

 places ; it is apparently the species that is most usually found 

 on board ships, where it sometimes multiplies enormously, and 

 entirely devours stores of farinaceous food to which it obtains 

 access : it is known that sometimes a box or barrel supposed to 

 contain biscuits, on being opened is found to have its edible con- 

 tents entirely replaced by a mass of living cockroaches. Fortu- 

 nately Periplaneta americana has not spread widely in this country, 

 though it is found in great numbers in limited localities; one of the 

 best known of which is the Zoological Gardens in the Eegent's 

 Park at London. Periplaneta australasiae is very similar to P. 

 americana, but has a yellow mark on the shoulder of each tegmen. 

 This has obtained a footing in some of the glass-houses in the 

 Botanic Gardens at Cambridge and Kew; and it is said to be fairly 

 well established in Belfast. Another of our introduced domestic 

 cockroaches is Phyllodromia germanica, a much smaller Insect 

 than the others we have mentioned. It has only established 

 itself at a few places in this country, but it is extremely abundant 

 in some parts of Northern and Eastern Europe. It has been in- 

 creasing in numbers in Vienna, where, according to Brunner, it is 

 1 Schiifr, Zool. Anz. xvi. 1893, p. 17. 



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