360 MR. ROBERT SHELFORD ON 



all of them, are endowed with very distasteful properties. Rehn 

 and Hebard (Proc. Acad. Nat. Sci. Philadelphia, 1905, p. 32) 

 write of Eurycotis floridana Walk. : — " When seized these insects 

 emit a vile-smelling oily fluid. The females always produced 

 far more of this than the males." This is a chestnut-brown 

 species, but the larvse have the thoracic tergites margined with 

 pale yellow ; it is found hiding under logs and stones. It is 

 evident, then, that amongst the Blattidee a nauseous odour or 

 taste is not invariably associated with aposematic habits, — the 

 insects themselves may be conspicuous enough when unearthed 

 from their hiding-places, but the point is, that they do not 

 voluntarily expose themselves, as do so many of the Australian 

 Polyzosteriae. Further confirmation of these rather puzzling 

 facts is afforded by observations made by Mr. G. A. K. Marshall 

 on two South-African cockroaches, Deropeltis e.rythroce'pJiala Fab. 

 and Aptera fasca Thunb. The first of tliese belongs to the sub- 

 family Blattinpe and to a genus in which the males are winged 

 and the females apterous. In both sexes the posterior margin 

 of the fifth abdominal tergite is sinuate *, and beneath the tergite 

 are situated glands from which a sticky fluid exudes when the 

 insects are seized. Though it is reasonable to suppose that this 

 fluid is a distasteful secretion of a defensive nature, it must again 

 be noted that D. erythrocephala and probably most of the othei' 

 species of the genus hide beneath stones and do not expose them- 

 selves voluntarily. Most of the species of Deropeltis are bulky 

 insects, piceous in colour ; in D. erythrocephala the head and legs 

 are red. D. dichroa Gerst., from the Gold Coast, has a lai-ge 

 fulvous macula on each side of the sixth and seventh abdominal 

 tergites ; whilst D. paulinoi BoL, from Angola, is equally conspi- 

 cuously marked with rufous fasciae on the lateral margins of the 

 pronotum. The female of Aptera fusca, one of the Perisphseriinaa, 

 is a large, robust insect, piceous with conspicuous transverse 

 bands of ochreous or rufous ; when seized it exudes a violet fluid 

 which stains the fingers ; this species also has cryptic habits. This 

 is absolutely all the information that I have been able to gather 

 about unpalatable species of Blattidse, and it certainly is little 

 enough. It is perhaps remarkable that the undoubtedly nauseous 

 Australian species are not mimicked either by other orders of 

 insects or by non-distasteful species of Blattidse, but it must be 

 remembered that the Orthoptera do not serve as niodels to other 

 orders of insects — not a single instance has ever been recorded, 

 and in Australia the paucity of cockroaches other than those of 

 the distasteful group, is quite exceptional. 



Although no Blattidee are known to serve as models to mimick- 

 ing insects, there are several which mimic insects other than 

 Orthoptera, though in most instances the mimicry is of a very 

 generalised nature. I have no reason to suppose that any of 

 these mimetic Blattidfe are other than palatable. 



* A generic character. 



