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.
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 wastes (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.”