258 
2. Observations on the destructive species of Dipterous 
Insects known in Africa under the names of the 
Tsetse, Zimb, and Tsaltsalya, and on their supposed 
CONNEXION WITH THE FOURTH PLAGUE OF EGYPT. By 
J. O. Westwood, F.L.S., Pres. Ent. Soc. etc. 
(Annulosa, PI. XIX.) 
The species of insects which attack the larger of our domestic qua¬ 
drupeds may be divided into two chief classes ; first, those which do 
so in order to obtain a supply of food for their own support; and 
second, those which do so with the object of depositing their eggs in 
such a position, that the larvae, when hatched from them, will be cer¬ 
tain of finding a proper supply of food derived from some part of the 
animal, either external or internal. 
The insects composing the first of these two classes require for the 
performance of their dreaded functions an organization of the parts 
of the mouth especially fitting them to pierce the skins and hides of 
the quadrupeds upon the blood of which they subsist, and we accord¬ 
ingly find that it is precisely these insects which have the mouth- 
organs most fully developed in the different families to which they 
respectively belong. The Stomoxys calcitrans, and especially the 
different species of Tab anus, are pre-eminent in this respect; and 
the formidable array of lancets in the mouth of one of the latter 
insects is not to be met with elsewhere among the whole of the flies 
composing the order Diptera, to which they belong. The effects of 
the attacks of these insects upon the horse are perceived. by the 
drops of blood which flow from the orifices caused by their bites, 
and sometimes these wounds are so numerous, that the beasts “ are 
all in a gore of blood.” A still smaller species, named by Linnaeus 
the Culex equinus , also infests the horse in infinite numbers, running 
under the mane and amongst the hair, and piercing the skin to suck 
their blood. This insect, although given by Linnaeus as a Culex , 
appears from his description to belong to the genus Simulium, to 
which genus also belongs an insect of fearful note, which attacks the 
horned cattle in Senna and the Bannat, penetrating the generative 
organs, nose, ears, &c. of these animals, and by its poisonous bite de¬ 
stroying them in a few hours. A species of the same genus of minute 
Tipulidce is common in marshy districts in England, and I have often 
experienced its attacks, which have resulted in the raising of a tu¬ 
mour on the part of the flesh which has been attacked, attended by a 
considerable amount of local inflammation; and hence we may readily 
believe the well-authenticated effects produced upon the cattle above 
described. There are various other insects which attack the horse 
and ox, such as the Hippoboscce , various species of ticks, Anthomyice, 
&c.; and if these do not, from their smaller size, cause a discharge of 
blood like the large Tabanidce, it is certain that the irritation which 
they produce not only by their presence upon the skin, but also by 
the sharpness of their bite, must be very irritating to the quadrupeds 
which they infest. 
