140 Zoological Society. 



rect conjecture, as the CEstri, if they make any hum at all, are far out- 

 stripped in this respect by many other insects which instil no dread 

 into oxen. Neither are they alarmed in consequence of being sub- 

 jected to the same kind of attack upon so sensitive a part as the lips, 

 as is the case with the horses attacked by (Estrus hfBmorrhoidalis. It 

 is however asserted by some writers, that the dread is produced by 

 the pain inflicted by the (Estrus in depositing her eggs, her ovipositor 

 being represented as constructed like an auger or gimlet, only having 

 several longer points it can wound with more effect. When it is stated, 

 however, that the female CEstrus Bovis does not occupy more than a 

 few seconds in depositing each egg, we may fairly doubt whether, with 

 her long, fleshy, tubular ovipositor, she has been able to pierce the 

 hide of an ox ; or whether, as Mr. Bracy Clark suggests, she only 

 makes use of this long instrument to thrust the egg down to the sur- 

 face of the skin, which she does not pierce, but only glues its eggs to 

 it, the young larvae when hatched burrowing into the flesh. If this 

 be the case, the act of oviposition must be unattended with pain, as in 

 the case of the deposition of the eggs of CEstrus Equi, and we must 

 search for the cause of the alarm of the herd, either in an instinctive 

 knowledge that a certain insect flying around them is the parent of a 

 grub which at a future time will be a torment to them, or in the attacks 

 of some other insect ; and I confess that I am inclined to consider that 

 Virgil's beautiful description of the annoyance caused by 



'* Myriads of insects fluttering in the gloom, 

 {(Estrus in Greece, Asilus named at Rome,) 

 Fierce and of cruel hum " — 



has a Tabanus rather than an (Estrus for its origin. 



The larva of the (Estrus Equi resides beneath the skin of the back 

 of the ox, causing large tumours, and having the extremity of its 

 body constantly placed at the orifice of the wound, where it was in- 

 troduced as an egg, or introduced itself as a grub, the openings of its 

 respiratory apparatus being placed at that part of the body. 



These introductory remarks on the different modes in which insects 

 attack our horses and oxen, and the different effects which they pro- 

 duce, will enable us the better to estimate the effects produced by an 

 insect, or several species of insects, of tropical Africa upon the horses 

 of travellers who have lately returned from that part of the world, 

 where their enterprising researches have been rewarded by the disco- 

 very of the great central lake Tchad. Captain Frank Vardon, a gen- 

 tleman who has travelled far in the interior of Africa, has placed in 

 my hands some fragments of Dipterous insects which attacked his 

 horses, causing the death of one of them. The following is an ex- 

 tract from his note to me in reply to my inquiry as to the mode of 

 its attack : — 



" 33 Oxford Terrace, Hyde Park, May 1850. 



"Dear Sir, — I had always heard that the fly of South Africa so 

 destructive to cattle was a large gad-fly, the size of a bee or hornet. 

 This is quite erroneous : it is not very much larger than the common 

 house-fly, but a longer and more 'rakish '-looking insect, and easily 

 distinguished by the transverse black bars on its body. 



