The Ant World Seen Inside Out
THE ANTS by Bert H"olldobler and Edward O. Wilson, Cambridge, Mass.: Belknap Press, Harvard University Press, 732 pp., $65 ANTS are fascinating but often ignored. Looking closely at the moving mound of earth called an ant colony, one discovers thousands of workers marching to and fro, nurturing young that are not their own, not hesitating to set out on nearly suicidal foraging expeditions, and defending the homestead to the death. All in service to their queen.
A huge majority of ants are members of a sterile-female worker caste whose altruistic and highly social behavior has not only astonished, but stumped, many an observer.
How could a caste of nonreproductive workers have evolved, since they leave no offspring? How could such altruism come about, given the process of natural selection in which the best adapted individuals are most likely to have their genes represented in future generations?
Other ant phenomena are equally as curious. One species of slave-making ant releases a special chemical when raiding the nests of another species. This ``propaganda substance'' causes the ants under attack to fight each other. The slave-makers are then free to steal ant larvae, which become enslaved workers.
Then there's the commonplace but mysterious ant-train: hundreds of ants, each diligently following the precise path of the ant in front of her. The result is a serpentine journey, sometimes over rocks that could have been avoided had any individual ant stopped to take a look around.
``The Ants,'' by Bert H"olldobler and Edward O. Wilson, will be praised by the scientific community, yet it's enjoyable at several other levels. The language is often technical and the authors even use mathematical models, but the writing is straightforward enough to engage any interested reader. Both authors are renowned in their respective fields, and Dr. Wilson wrote the Pulitzer Prize-winning ``On Human Nature.''
Through ``The Ants,'' armchair science fans not only become familiar with the ant, but they also get a basic lesson in biology and a realistic look at how science sometimes progresses as a result of tension between the leanings of different scientists.
Take, for example, the authors' clear-cut definition of kin selection. This basic biological concept explains how nonreproductive and altruistic workers found among ants, bees, termites, wasps, and several other insects, might have evolved:
``By reducing personal survival and reproduction, workers nevertheless increase the survival and reproductive genes they share with members of the colony by common descent. Individuals suffer, but the colony flourishes and so do the genes (including the altruistic genes).''
The authors then present competing theories and conclude that, while the balance has tipped in favor of kin selection, it is still too early to rule out other explanations.
The first section of the book set ants apart from the rest of the insect world, and their distinctive species apart from each other. Ants are at the pinnacle of insect evolution just as human beings are the culmination of vertebrate evolution.
The next section describes more specifically what goes on within and between ant colonies: kin recognition, chemical communication, specialization among the worker castes, foraging strategies, and competition among species.
In the chapter on ``Communication,'' the authors explain the ant-train phenomenon. Ants follow each other so meticulously because they are following a chemical trail. In one particular species, researchers have found that the number of workers who search out a food source is controlled by these chemical trails.
When an ant scout first finds food, she will lay a chemical trail back to the nest using a gland located near the stinger. Nest-mates will then follow her rapidly dispersing trail. The number of ants that leave the nest is proportional to the amount of chemical emitted.
At first there is a buildup of workers on the food source. Because of the crowd, newly arriving ants may then decide not to lay a trail back to the nest. The trail gets weaker, fewer ants go to investigate, and the crowd levels off. Thus the quality of a food find, and in some species, the quality of a nest site, can be communicated by the workers' ability to vote with their chemical trails after inspecting the find or site.
The third section describes the symbiosis among ant species with other anthropoids and between ants and plants.
The last section is perhaps the most intriguing for nonspecialists. These chapters zoom in on ``classic'' groups in the ant kingdom. One consists of migratory army ants, which form hanging, cornucopia-shaped nests out of their own living masses. The chapter on the fungus growers or leafcutter ants explains their symbiotic relationship with a fungus that they cultivate by using collected plant material (see illustration).
The authors describe the nest building of the classic weaver ant as the ``pinnacle of altruistic cooperation.'' These ants work together to maneuver leaves into a partially enclosed shape. Individual ants then begin to weave a nest around the leaves with larvae that produce silk on the spot. The last chapter is a short one on collecting, culturing, and observing ants.
This book will be the centerpiece in ant science (myrmecology) for many years to come. It includes a 48-page taxonomic key, 58 pages of corresponding drawings, vivid photographs, detailed illustrations and tables, a 10-page glossary (which might have been more generous for newcomers), and a large bibliography. It is a treasure chest for science teachers and those to whom it is dedicated - future ant scientists.
The two authors themselves exhibit their subjects' principal virtue - industry. Readers with a little of the same virtue will be more than repaid with fascinating and original insights. .
As Proverbs advises, ``Go to the ant, thou sluggard: consider her ways, and be wise.''