Forces affecting water imbibition inMacrotermes workers (Termitidae,Isoptera)

Summary Observations of putative drinking behaviour at soil surfaces by major workers ofMacrotermes subhyalinus andM. bellicosus suggested that unidirectionally arranged trichomes on the anterior hypopharynx exert capillarity on water in soil pores. To test this hypothesis thirsty major workers were placed on soil of relatively low water content. From the soil types tested we determined soil-moisture retention curves which represent graphically the water content of the soil and its corresponding capillary potential. The termites were able to obtain water from different types of clay soil against potentials in the range – 1.6 to – 1.9 bar. On sandy soil the capillary potential was found to be much higher (– 0.18 bar), i.e. closer to zero. Sandy soil has a very unfavourable water retention capacity, i.e. its water content is very low at low capillary potential, whereas clay soil retains much more water at low capillary potential. The ability of the termites to gain water from soils with relatively low water content is an important adaptive feature for survival in semi-arid areas.