THE SOCIAL INSECTS 



no longer effective throughout, and substitute sexual forms 

 may develop. Such outlying sections of the colony may 

 eventually bud off, like the small bulbs found round a larger 

 one. Much less commonly, in a few kinds of termites, more 

 active splitting up of the colony has been observed, with all 

 its members walking out of the nest, carrying the eggs and 

 young larvae, and breaking up into groups, one with the 

 original royal couple, the others with substitute sexual forms. 



The ability to produce these substitutes means that a 

 termite colony is potentially immortal, since its repro- 

 ductive functions can always be renewed. It seems, however, 

 that in many species substitute sexual forms do not play the 

 important role which they do in laboratory experiments. 

 Except in certain species, they seem to be relatively un- 

 common, probably coming into play when one of the royal 

 couple is lost in some rare accident. There is some evidence 

 that as the colony gets older, substitute forms are even less 

 effective, so that in reality most termite nests probably last 

 only a moderate number of years. 



Calotermes colonies usually appear to survive for twelve 

 to fifteen years. Other species in which substitute sexual 

 forms are produced more regularly and in larger numbers 

 may well last longer. The very large colonies of the higher 

 termites must certainly be long-lived, if only because the 

 huge nests must be constructed over a long period. Hill has 

 recorded that the top of a large Australian steeple-like nest 

 was knocked off in 1872 to allow a telegraph wire to pass over 

 it and that the colony was still flourishing in 1935, when it 

 must have been much more than sixty-three years old, per- 

 haps nearly one hundred years. Apparently, the original 

 royal couple are indeed able to live for a period as long as 

 this, a much longer period than has been recorded in any 

 other insect. 



188 



