C. Warburton 
320 
The best observers are now agreed that Hypoderma is the sole cause of 
“gadding” in cattle. Carpenter and Steen (1908) note that “while the presence 
of numerous clegs ( Haematopota ) does not lead to any visible disturbance 
among the animals, a calf, the moment he is touched by a warble-fly, becomes 
frantic and goes off at a bound.” The cause of terror has always been a puzzle, 
since no pain is inflicted. In the following passage Carpenter (1914) suggests 
an explanation. “We found that the calves became annoyed and excited 
and commenced to gad if touched on any part of the legs or flanks, but they 
did not stir if touched on their backs. This led us to conclude that the mere 
irritation caused by the fly touching the calf in its persistent attacks is enough 
to cause the animals’ gadding and terror; they cannot get rid of the fly unless 
they plunge into a river, or find shady shelter.” Loss of condition and of milk 
due to “gadding” are among the recognised ill-effects of warble-flies. That 
they may also cause serious inconvenience is well illustrated by an anecdote 
of Hadwen (1912) from Alberta. He one day met a cow-boy who seemed to 
be vastly amused at something, and who, on being asked the cause of his 
merriment, said: “Well; I came riding by a little lake just now, and I saw 
some cattle standing in it with their yokes on. A disconsolate settler was 
sitting on the bank, who said that he was waiting for them to come out with 
the plough, and that he would not get much ploughing done if the flies did 
not stop chasing his cattle into the water.” Gadding with a plough is not 
unattended with danger, and a contrivance is in use in some districts by which 
the oxen are automatically released from the implement in case of a sudden 
dash away. 
Carpenter and Hewitt published in 1914 (Carpenter 1914) a description 
of the reproductive organs of the warble-fly. They were apparently unaware 
of the previous work of Joly in this field. 
Oviposition. 
Though oviposition was not observed in case of either fly till 1892, the 
egg of H. bovis was described and figured by Reaumur (1738). He, and several 
of his successors (e.g. Brauer, 1863) obtained it by expression from the ovi¬ 
positor of a captured fly. The early view was that the back of the cattle was 
pierced by the ovipositor, with the infliction of great pain—hence the gadding— 
though Reaumur could find nothing of a piercing nature in the ovipositor 
except the minute chitinised points at its extremity. He, indeed, was some¬ 
what sceptical of the extreme suffering of animals so tolerant of the goad. 
Nor would he adopt Vallisnieri’s view that a poison was inserted with the 
egg. Though the unsuitability of the ovipositor of Hypoderma as a piercing 
instrument was thus long ago demonstrated, the early view of oviposition 
was so firmly established in popular belief, thanks largely to Bracy Clark’s 
“Essay” (1815), that Miss Ormerod (1884-94) only abandoned it towards the 
end of her investigations. She did, in her later papers, admit that the piercing 
theory must be abandoned, and held that the flies probably deposited their 
