Sex on Six Legs_ Lessons on Life, Love, and Language From the Insect World - Marlene Zuk [94]
Microscopic Real Estate
PEOPLE have long taken a personal interest in the real estate preferences of honeybees, mainly because the product of a smoothly running hive is relevant to human well-being. They have been less concerned about the decisions made by other social insects, such as ants, so long as they do not decide to relocate in or near human habitation. The house-hunting behavior of ants, however, is both similar to and different from nest site selection in honeybees, and the contrast is instructive.
Much of the research on group decisions by ants on where to live has centered on a couple of species with life histories that sound like they come from a fairy tale, or maybe a Winnie the Pooh story. The insects are even tinier than the ants commonly seen in kitchens, and use either rock crevices, or, more charmingly, acorns, as their place of residence. The entire colony, queen and all, can fit into a space smaller than a person's thumb. Needless to say, this makes replicating their world in the laboratory extremely easy; one of the foremost researchers on these ants, Nigel Franks of the University of Bristol, makes little homes for them by gluing a bit of cardboard between two glass microscope slides to recreate a crevice that is also easily spied upon.
The ants' house-hunting activities have attracted attention mainly because they use the tandem running procedure I described in the chapter on learning to help their nest mates find the new location. As in the bees, ants send out scouts to search for new homes, but unlike the bees, the scouts enlist enthusiasts for the new cavity by the same "follow me" motions used to direct other colony members to food sources. The ants don't perform waggle dances like the bees, but they will recruit for good sites more quickly than for poorer ones. The new recruits, if they concur with the desirability of the chosen location, then get others to join them. If you are an ant living in a small dark hollow, the best home has a narrow entrance with dim light, presumably to discourage predators, and just the right amount of floor space. The ants can even evaluate the potential for nasty neighbors, in the form of a foreign ant colony, and eschew such potentially troublesome locations.
At this point the process diverges from that of the bees, because once a site is selected by enough ants, the process becomes one of shanghai rather than persuasion, as the remainder of the colony is simply picked up bodily and carried, head ignominiously pointing backward, to the chosen location. Carrying is three times faster than tandem running, and once the carrying starts, the ants are committed to their new location and do not switch preferences in midstream. Regret, it would seem, is not part of the ant repertoire. As a paper by Robert Planqué and his collaborators, including Franks, puts it, "Ant colonies have found a good compromise between impatience and procrastination." Would that we were all so prudent, at least when it comes to moving house.
In human groups it's often the case that the larger the crowd, the harder it is to reach a decision, whether about going to war or choosing a restaurant. In contrast, the ants seem equally good at determining the best nest site from among an array of options presented in the laboratory regardless of the size of their colony. The larger colonies do use more of the tandem runs to exhort others to follow them, and seem to need a larger quorum of assenting individuals before they decamp. Interestingly, both small and large colonies select sites that will comfortably contain a colony that has grown to full size, suggesting that the ants can anticipate their future needs, a remarkable feat.
Franks and his colleagues demonstrated this ability of ants to plan by showing that they can distinguish between various