Common Name: Allegheny Mound Ant – The Allegheny plateau is geographically central to the eastern region of North America that comprises the habitat of eponymous ant. It is noted further for its construction or large nests in the form of mounds.
Scientific Name: Formica exsectoides – The generic name Formica is Latin for ‘ant.’ The species name is related to the verb ‘to exsect’ which means ‘to cut out;’ the addition of the suffix ‘oides’ indicates that is an animal that does this. This is likely due to the fact that this species is noted for cutting out the vegetation around its mound nest for environmental reasons.
Potpourri: The Allegheny mound ant stands out from the overwhelming ubiquity of the hymenopterous insects (this includes the ants in additions to bees and wasps) in its being at the same time a red ant and a black ant, as if Stendhal had something to do with it. The colorful dichotomy does not in any way detract from its individuality as the largest mound builder among the field ants, i.e. those of the family Formicidae which are also sometimes called wood ants, and for its other contrarian characteristics of having multiple queens and multiple interconnected nests in an ant megalopolis inevitably called a supercolony. With their ferruginous head and thorax coupled to their black abdomen or gaster, Allegheny mound ants cannot be missed and they should not be be dismissed; even large ambivalent intruders are met with a barrage of formic acid spray and a vicious bite amplified by literally thousands of individuals in their singular acts of eusocialistic behavior.
The mound is a surprising architecture for the nest of an insect, as stealth and sequestered secrecy are the more prevalent defense mechanisms; other ants build nests underground away from the ravages of the elements and the predation of insectivores. There are several advantages to mounded convexity that were manifest to the earliest researchers. In the seminal 1810 work by Pierre Huber, Recherches sur les moeurs des fourmis indigènes (translated into English in 1820 as The Natural History of Ants) he writes of the remarkable mounds as “an invention as ingenious as simple to carry off the waters from the ant hill, to defend it from the injuries from the air, and from hostile attacks, and to regulate the heat of the sun, or to retain it in the interior.” While one may argue whether an above ground nest is a better defense (I think not), advanced temperature control has been confirmed and quantified by subsequent field studies. The mound is the antithesis of a pile of dirt, a fata morgana when encountered trailside; it is an intricate anastomosis of interconnecting tunnels and airways that serve to regulate the temperature inside to that which is optimum for the processing of new adult ants from the egg and larval stages. Even the mound’s orientation may reflect the climactic, as the southern facing slope is typically elongated to favor early spring warming to energize the productivity engine of the eusocial colony.
Eusociality is the relatively modern biological term that refers to a form of society in which there are multiple generations of individuals that are inclined to perform altruistic acts according to their assignation in a deterministic division of labor. Ants instantiate eusociality, posing a serious conundrum to Charles Darwin, whose survival of the fittest foundations were shaken by the altruistic behaviors of the sterile, altruistic worker ants. Writing in The Origin of Species, he notes that this “at first appeared to me insuperable, and actually fatal to my whole theory.” How could an organism evolve when its actions acted in contradiction to its genetic heritage – workers who willingly sacrificed themselves could not possibly survive? Altruistic behavior remains a subject of serious debate in biology. The first coherent theory was formulated by William Hamilton in 1964 based on the observation that an altruistic act would occur if the benefit (B) of an action would exceed the cost (C) of the action if relatedness (r) were taken into account. According to what is now called the inclusive fitness theory, if rB >C, then the individual would act because his or her genetic (related) benefit would be advanced. The theory gained credence according to one of the more unusual characteristic traits of many eusocial insects with the mellifluous name haplodiploidy. Females come from fertilized eggs and are diploid (having a double set of chromosomes, called 2n) and the males come from unfertilized eggs and are haploid (having a single set of chromosomes, n); when the queen mates with one of the males, the result is haplodiploidy. The end result is that each female offspring will have all of the father’s genes and half of the mother’s so that each sister shares three-quarters of their genes with the cohort, and, since they are more closely related to each other than to anyone else, then rB>C as far as the colony is concerned whenever they are self-destructively altruistic.
The Ockham’s razor logic of Hamilton’s inclusive fitness theory has not stood the test of time, as more recent research revealed that some eusocial insects are not haplodiploidy and some insects that are haplodiploidy are not eusocial. Edward Wilson, a renowned biologist professor emeritus at Harvard offers a radically different hypothesis in his recent controversial book The Social Conquest of Earth. He proffers a much more nuanced syllogism that social insects like ants and termites are related because they are eusocial, not as a result of it. As a matter of entomological interest, he notes that you can tell an ant from a termite because ants have waists (they evolved from wasps) and termites don’t (they evolved from cockroaches). The origins of eusocial behavior is purported to begin with a defensible nest which favors evolutionary changes that promote it, such as a central location to nurture and the streamlined sexuality of haplodiploidy. The diversity of body forms, workers, soldiers and drone males evolved due to “extreme plasticity of certain genes, programmed so that the altruistic workers have the same genes as the mother queen, even though they differ drastically from the queen and each other in these traits.” Wilson’s “group theory” approach was favored by Darwin, who rationalized in The Origin of Species that altruism could result when “selection may be applied to a family as well as to the individual and thus gain the desired end.” Whatever the cause, eusociality is surely as rare (only 15 of 2,600 insect families are eusocial) as it is successful (two German zoologists weighed all of the insects in a hectare of rain forest and found that two thirds of the weight were ants and termites). Wilson estimates that there are ten thousand trillion (1016) ants in the world – one million ants for every human. A large Allegheny mound ant colony can contain as many as 250,000 individuals.
The life cycle of ants in general and the Allegheny mound ant in particular offers a combination of aesthetically balanced phenomena that would have to qualify as a natural Gesamkunstwerk, though perhaps orchestrated by Aaron Copeland instead of Richard Strauss. The cycle begins with the dispatch of a winged virgin queen from an established nest to consummate the sexual act with one of many winged males, alighting soon thereafter at a hopefully habitable site for colonization; the ennobled single male dies shortly after depositing his sperm into the queen’s seminal receptacle called the spermatheca. Following removal of the now superfluous wings (a vestige of wasp ancestry), the impregnated queen excavates enough dirt to form a nascent nest, therein to deposit and nurture the first brood. The control of egg fertilization by the queen is a nonpareil adaptation that borders on the miraculous. As the eggs are released down the oviduct, the queen chooses to release sperm from the spermatheca to result in a fertilized egg which becomes a female or not to release sperm to result in an unfertilized egg which becomes a male, thereby controlling the sex ratio of the colony. In that the task of raising the first brood is arduously borne by the queen for the first generation, it is necessary that they are all female sister workers. The time from egg to adult is not trivial, ranging from 2 to 3 months. During this time, the queen hatches the eggs into legless and helpless white larvae that must be nourished until they pupate into adults. It is a wonder that colonies survive in light of the tenuous circumstances of their inception in the face of an unforgiving natural environment of predators and weather. The colony becomes established as the duties of nurturer are relegated from the queen to her daughters who carry out the larva tending role for subsequent generations of ants, and to the eventual construction and maintenance of the mound nest. Allegheny mound ants are unusual in that they tend to populate numerous mounds in a closely proximate supercolony each of which may have several queens. This is likely an adaptation to promote survival in compensation for the epic fragility of single queen colonization.
The dominance of the Allegheny mound ant in the immediate vicinity of the nest is both necessary and sufficient to provide sustenance to a burgeoning ant population of up to a million individuals. F. exsectoides exsect the trees and shrubs in the immediate vicinity of the nest, thereby justifying their taxonomic designation. Reducing the seasonal shadiness effect that foliage creates enhances the operation of the ventilated mound thermostat used to maintain ideal larval living conditions therein. The ants exsect the shrubs by chewing into the bark around the base of the tree and injecting formic acid into the wound, the damage, manifest as resin filled blisters on the bark, will eventually kill the tree. This practice has been observed as far as 50 feet from the nest on trees up to 8 feet tall. The formic acid, which is produced in a large sac in the gaster or abdomen, is a formidable chemical that is used in both protection and predation. In For the Love of Insects, Cornell ecologist Thomas Eisner observes that “the individual formicine ant, as it goes about its business, is thus to be viewed as a spray gun on legs.” The spray, which is up to 50 percent formic acid, is capable of subduing the many arthropods that the ant preys on in addition to providing a formidable deterrent against any invasive threats.
In addition to the scorched earth policy of vegetation excision, Allegheny mound ants are ranchers; they herd aphids. Aphids, like all of the ubiquitous insects, have evolved to occupy a specialized niche. They live by the thousands on vascular plants, extracting nutrition from phloem, the food carrying outer tissue (the complementary xylem tissue conveys the water up the inside of the plant). Since phloem is very low in nitrogen, the aphid extracts large quantities of it to process enough nitrogen for its own growth requirements. The excess passes through a specialized organ called a filter chamber directly to the anus, where it passes out as frass. Since it contains most of the sugars of the phloem, it is a highly enriched food source that is called, not surprisingly, honeydew (there is no relationship between aphids and honeydew melons). The nutritious honeydew is highly prized by the Allegheny mound ants to the extent that the aphids are guarded against predation by ant overseers, providing this service in reciprocity for the guaranteed food source. The ant – aphid mutualism is so beneficial and benign to both species that they have mutually proliferated. As Douglas Tallamy writes in Bringing Nature Home, “It is difficult to find an aphid aggregation that is not being tended like cattle by a group of ants.”