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Thursday, July 4, 2002
Welcome to the world's most successful societies
By MARK BRAZIL
Second of two parts Ants have an amazing lineage. They have been around for at least 100 million years, since the middle of the Cretaceous Period, and for at least the last 50 million years they have been among the most abundant of all insects. We think we're successful? Our population has recently topped 6 billion, but the great ant scientist, Harvard-based professor E.O. Wilson, has estimated there are about 1 million billion ants in the world.
In biomass terms, in just about any habitat, this means that ants outweigh all birds, amphibians, reptiles and mammals combined . . . several times over.
The ants' winning formula is their social behavior. Not only have they developed factory-like production lines based on division of labor, but they also create climate-controlled conditions inside their fortress-like nests (which they are prepared to defend to the death). Their control extends outside the nest, too. Ants modify their surroundings, and in their realm leave no potential food item unmissed and no enemy unfought. Indeed, ants are the most warlike of all known animal groups.
The persistence of ants is remarkable, and an e-mail from a friend working in Bohol in the Philippines says it all. Jeremy was making a documentary about tarsiers, those small tree-dwelling primates with goggle eyes and long, tufted tails, but it was other, far smaller creatures that were apparently commanding his attention.
He wrote: "I don't think we can say that we have actually won the battle with the ants, it's at a holding stage only. So far they have got into everything, everything except the fridge. But I am certain that when the power is off, which is often, even the fridge's defenses are not insurmountable. The house we are living in came with plastic holding boxes, large with hinged lids. For about a day the bread was un-anted, and then the half-loaf was covered, inside and out, mostly with tiny red-brown ants that seem to come from nowhere. Strike one to the ants.
"We bought a sealed container, sort of a Tupperware thing. That lasted half a day. Strike two to the ants. And the tiny red-brown ones are the worst.
"Next was the bread inside a plastic bag inside the sealed box -- no problem at all. Strike three to the ants.
"Then the bread was inside a sealed freezer bag, inside a tied plastic bag inside the container. That took about another half-day for the ants to solve. So now the bread is inside the fridge. The jar with the instant coffee is next to the jar with the sugar, which is an old coffee jar with a screw top, and both are standing inside a used ice-cream container surrounded by water. That's worked for a day or so, but I'm certain that the ants will learn to swim."
Not all ants are such persistent nuisances. In fact, I have always found the various wood ants of the genus Formica fascinating. These are the ants that dominate the forests of the northern hemisphere, using dried pine needles and twigs to build mound-like nests that may reach 2 meters high and be used for hundreds of years.
Though wood ants are large, reaching 1 cm in length, they are dwarfed by a species I have encountered several times in tropical South America. There, a monster ant that reaches 2 cm in length is known locally as "24 hours" -- a nickname derived from how long the pain from its bite lasts.
These fearsome creatures wander the forest floor in a seemingly solitary existence; I know nothing of their life cycle, though I have had some close encounters with them. Thankfully, none of these has been as close as that of a friend who accidentally knelt on one in a forest in Peru. He described the pain as like "being stabbed with a red-hot knife." Indeed, so searing was it that he said it knocked him over backward -- and yes, the agony lasted for 24 hours.
Thankfully there are no such aggressive monsters here, though wood ants' nests are easily found in mixed woodland in the mountains or the north. If you keep watch over any of the several trails radiating from a nest, you will see them carrying their scavenged insect prey home, but wood ants are farmers, too. They tend plant-sucking aphids, milking them for honeydew, as we milk cattle, yielding a food containing sugars, acids, salts and vitamins. The honeydew is food for the ants, which in return protect their precious aphids from predators and competing sap-sucking insects.
Wood ants are a "keystone species," a key element of a natural ecosystem, without which it changes fundamentally. For example, when wood ants are removed from forests, the ecosystem's predator-prey dynamics are affected, allowing herbivorous insects to become so numerous that they damage the trees.
Wood-ant colonies can number up to a half-million individuals, based on the typical ant pattern of long-lived queen, innumerable workers and short-lived males whose sole function is to mate. Their nests are clever, well-maintained constructions, providing protection from the elements and predators, and a constant stable environment suitable for eggs and pupae. The workers ensure that the temperature and humidity of the nest remain fairly constant -- in contrast to the surrounding soils. Those seemingly randomly piled needles are in fact carefully placed so that the domed roof sheds water and the southern side presents a flatter and larger area to the midday sun to absorb the maximum amount of solar energy.
Watch a nest in the morning and you will see columns of workers marching off along the regular trails that radiate from it. As predators they are able to detect their prey by vibration and scent. Small prey are stalked and pounced upon, whereas larger victims are subdued with the aid of nearby fellow workers. To back up their pincerlike mandibles, wood ants have another formidable way of subduing their victims and defending themselves when threatened. In the bulbous end-section of their bodies (the gaster), they have glands containing formic acid that can be sprayed accurately over distances up to 5 cm.
Japan is well-blessed with ants; there are at least 62 genera here, and the number of species runs into the hundreds. If I were not already an avid bird-watcher, it is to ants that I would devote my time. They may not be as colorful, and they lack vocalizations, but their fascinating social behavior beats anything birds have evolved.
A tremendous Web site called Japanese Ants Color Image Database can be found at ant.edb.miyakyo-u.ac.jp/INDEXE.HTM