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Feeding and Excretion in the Scorpion Paruroctonus Mesaensis: Water and Material Balance
1 Department of Biology, University of California at Riverside Riverside, California 92521, U.S.A
Scorpions feed by a process involving the external grinding and digestion of prey, with the ingestion of only the soluble fraction. The water obtained from the prey represents the most important source of water intake for scorpions inhabiting arid regions, placing great importance on the animals' ability to utilize prey water effectively. The scorpion Paruroctonus mesaensis (Stahnke) was found to ingest a mean of 88% of the body water of selected prey. However, the scorpion loses 0.37 ml of its own body water per ml of prey water extracted, resulting in a net water gain of 0.51 ml water for every ml of prey water. Fluid uptake by the scorpion has been ascribed to a pharyngeal pumping mechanism. Direct measurements of the suction generated by the pharynx yielded a minimal estimate of its pumping capability of 130mmHg.
The uptake and excretion of nitrogen and electrolytes by Paruroctonus mesaensis on a diet of Tenebrio molitor adults were also analysed. Almost all the potassium ingested was excreted, whereas most of the sodium and chloride were retained, possibly serving to expand haemolymph volume. Assuming a steady state for nitrogen, it was estimated that the net utilizable water obtained from prey, that is the water intake minus the excretory water necessitated by nitrogen excretion, was equivalent to about 35% of the initial prey water or 69% of the water ingested.
Key words: Arachnid physiology, water balance, feeding
Accepted on December 2, 1983
