Geotaxis in Poecilocems hieroglyphicus (Acrididae: Pyrogomorphinae)



The tendencies of Poecilocems hieroglyphicus (Klug) to crawl up slopes was studied in a cage placed at different inclinations. The interaction of negative geotaxis with photopositive responses and positive reaction towards the odour of food was also investigated. The suggestion is made that the gravity receptors are situated internally and are stimulated by changes in internal pressure distribution. Hair-plates at the leg-joints were found to play an essential part in adjusting and correcting the position of the legs during crawling.


Adults and mature nymphs of Poecilocerus hieroglyphicus (Klug) show pronounced negative geotaxis and crawl up slopes at higher angles of inclination.

Under normal conditions negative geotaxis dominates photopositive responses and the positive olfactory reaction to food. The latter response is only restored after a period of starvation exceeding 26 hours.

The sense organs mediating orientation towards gravitational forces may be internal being stimulated by differential pressures in the haemocoel.

I wish to thank Professor J. L. Cloudsley-Thompson for reading and correcting the manuscript.