352 
Parasites of Common Flies 
pairs of legs, and the procedure is usually rapid. When the anterior pair of 
legs is employed for this purpose the fly balances itself on the posterior pair 
and the opposite middle leg with its body tilted so as to slightly raise the side 
on which the operation is about to take place. Then the middle leg is brought 
forward, and rubbed between the anterior legs (PI. XVIII, figs. 4,17,18). When 
the posterior pair is used the fly balances itself on the anterior pair and opposite 
middle leg with the abdomen raised and the middle leg is rubbed between the 
posterior legs (PI. XVIII, fig. 19). A single anterior or posterior leg is never 
employed in cleaning a middle leg. 
The abdomen is cleaned by passing one or other of the posterior legs over 
its dorsal surface from its proximal to its distal end. 
The dorsal surface of the thorax is cleaned together with the upper surface 
of the wing, the movement of the leg commencing near the head of the fly. 
When the head is about to be cleansed the middle legs are thrust forwards, 
and the anterior legs applied to the sides of the head in such a manner that 
DESCRIPTION OF PLATE XVIII. 
Photographs, natural size, of male S. carnaria cleaning themselves out-of-doors. Exposure sec. 
Figs. 1, 2, 3. Some of the positions assumed when the anterior legs are being rubbed together. 
The middle pair of legs are directed forward in order to maintain a steady position. 
Fig. 4. The two anterior and the left middle legs are being rubbed together, while the body is 
balanced on the other three legs. 
Figs. 5, 6. Positions assumed when the posterior legs are being rubbed together. The middle 
legs are now directed backwards. 
Figs. 7-12. Some of the positions assumed when the wings are being cleaned. In all cases the 
middle legs are directed backwards. Fig. 7. The right posterior leg resting on the proximal 
part of the right wing, while the left posterior leg is being elevated preparatory to being applied 
to the upper surface of the left wing. Fig. 8. The left posterior leg passing down the upper 
surface of the left wing; the right posterior tarsus is under the tip of the left wing. Fig. 9. 
The distal part of the right wing clasped between the two posterior legs as they are drawn 
backwards. The wing has been so bent that upper surface is directed outwards. Fig. 10. 
The posterior legs passing over the upper surfaces of the wings. Fig. 11. Left wing about 
to escape from the embrace of the posterior legs. Fig. 12. Wings bent and applied to the 
sides of the abdomen by the pressure of the posterior legs. 
Fig. 13. The anterior legs being rubbed together. Middle legs directed forwards. Side view. 
Fig. 14. The proboscis being cleaned with the aid of the anterior legs. Middle legs directed 
forwards. Side view. 
Figs. 15 and 16. The posterior legs being rubbed together. Middle legs directed backwards, 
side view. 
Figs. 17 and 18. Anterior pair and right middle leg being rubbed together. Side view. 
Fig. 19. Posterior pair and right middle leg being rubbed together. 
Fig. 20. Head being cleaned between the anterior legs. 
Fig. 21. Right wing elevated by right posterior leg beneath it; left wing depressed by left posterior 
leg passing over it. 
Fig. 22. Both wings depressed by the posterior legs passing over them. 
Fig. 23. Both wings elevated by the posterior legs beneath them. 
Fig. 24. Posterior legs raised before application to the wings. 
Figs. 13-24. The flies are resting on the edge of a piece of plate glass. 
