FORCES AFFECTING WATER IMBIBITION IN MACROTERMES WORKERS (TERMITIDAE,ISOPTERA)

Observations of putative drinking behaviour at soil surfaces by major workers of Macrotermes subhyalinus and M. bellicosus suggested that un idirectionally arranged trichomes on the anterior hypopharynx exert ca pillarity on water in soil pores. To test this hypothesis thirsty majo r workers were placed on soil of relatively low water content. From th e soil types tested we determined soil-moisture retention curves which represent graphically the water content of the soil and its correspon ding 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 unfavo urable 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 or the termites to gain water fr om soils with relatively low water content is an important adaptive fe ature for survival in semi-arid areas.