— This article by Jerry Cates, first published on 19 April 2010, was last revised on 24 April 2016. © Bugsinthenews Vol. 11:04(10).
Every spring, throughout Texas and most of the southern half of the U.S., soon after new growth erupts from leaf buds, acrobat ants — in the genus Crematogaster — sally forth from their winter nests. Then, depending on whether or not they cultivated a winter population of homopteran scales, mealybugs or aphids in their nests, they either begin herding that extant population, or begin to seek out external populations of local homopterans to domesticate.
“Herding” is one way of saying they pick up the scales, aphids, or mealybugs in their jaws, move them to the new growth, and gently deposit them there to graze the local food supply. Before long, the homopteran plant parasites are once more hard at work, sucking the juices of the tender botanicals, and producing copious amounts of sweet honey-dew for the ants to drink.
Thus fortified, the ants–whose numbers had thinned during the winter months–soon multiply, striking fear in the hearts of sentient humans who spy their long columns of swift-moving ants on trees, shrubs, and homes, or who find the piles of chewed wood and chunks of insulation these ants often deposit in window sills while nesting.
However, it is a lack of familiarity with these ants and their biology that creates this unwarranted fear. Once one knows the lore surrounding these interesting creatures, fear of them — and of the supposed damage they cause to wood, foam insulation, and structural members of homes — dissipates.
They are not nearly as formidable as they first appear. Nor are they as destructive as their digs portend. But some humans, and most animals, spend their entire lives unaware of these truths. There are good reasons for this, as the following material explains.
When we see one of these ants, this (the photo below, at left) is the view we are typically treated to. Notice the elbowed antennae, which distinguish the ants from other arthropods. Now take note of the heart-shaped abdomen. This along with one other anatomical feature, distinguishes the acrobat ant from other ants in the Formicidae family.
Now, while I have your attention, take a good look at the posterior tip of the abdomen of the ant in fig 101. See how pointed it is? What would you expect to see emerging from that pointed tip? If you expected to see an operable stinger, you are up there with perhaps 99.999% of the rest of humanity, along with most of the animals that meet these ants in the wild.
But you would also be wrong.
The acrobat ant carries, in its external anatomy, all the earmarks of a formidable stinging machine. In fact, it is so formidable-appearing that most humans and other animals avoid it at all costs, out of fear that its potent sting will produce much pain, perhaps even a lasting mark, and — for animals more its size — possibly a fatal injury. However, appearances can be deceiving, and in this case they are.
And thereby hangs a tale.
Eons ago, according to evidence displayed in amber records, the acrobat ants separated from their close relatives when a chance genetic mutation happened to move the attachment of its pedicel (the stalk that connects the thorax to the abdomen) upward on the abdomen. Instead of attaching at the most anterior portion, the genetically aberrant pedicel attached above the midline, slightly further back on the abdomen’s dorsal surface. This anomaly gave its bearer the unusual ability to swing its posterior abdomen upward, where its (presumably) then-potent stinger could be used as a defense against predators who approached from that direction.
Because of this capability, the mutated ant thrived and multiplied, particularly in the open, on shrubs, leaves, and stems, where ordinary ants are snatched up or otherwise attacked by their natural predators (who were now given pause by the ant’s ability to sting them more readily) in an instant. The success of this mutation favored other anatomical changes as well. One of those was the strengthening of musculature and tendon attachments, but only on either side of the pedicel attachment, inside the abdomen.
These — one might guess — partially explain why the abdomens of acrobat ants are broader anteriolaterally (on the sides of the abdomen near the pedicel) than those of most other ants, giving their dorsal and ventral aspects the shape of a heart.
Every bit of protein needed to develop and maintain the ant’s body takes away from resources used for metabolism, reproduction, and other processes. The added musculature and tendon attachments, though costly accouterments, were worth the price because they helped the ant live a longer, more productive life. However, every new opportunity to economize helps. And, as chance would have it, over time many economical opportunities arrived in the form of fresh genetic mutations that, under ordinary circumstances, might otherwise have spelled disaster. A later acrobat ant was born, for example, with all its faculties intact but one: its stinging apparatus was less efficient than before. Either the stinger itself was too small, or too frail, or the venom glands produced a lower quality of venom or none at all. In any case, the ant was unable to sting an attacking predator with the same potency as before, though it could still make as good a show of “trying” to as the next one.
This entirely or partially impotent ant could still swing its abdomen up in a fearsome-looking display when a predator threatened to snatch it. But that was about the extent of its defensive repertoire. It was, as we say in Texas, all hat and no cattle.
So, that was the end of that ant, right? Wrong! Not only did the less potent form of the acrobat ant survive, it thrived slightly better than its more potent relatives. They were forced, by their genetic natures, to expend considerable energy producing strong venom and hardened stingers, while the mutant could use that same energy for more productive pursuits. The mere act of swinging its abdomen upward in a threatening gesture was sufficient to frighten away even the most ardent predator. Stinging them wasn’t quite as necessary, just a good show of force.
And that — from all indications — is probably one of the reasons why, today, acrobat ants have spatulate stingers and, in many cases, smaller venom glands that produce a somewhat less virulent venom than many of their cousins, and why many species can’t sting a soul, even if their lives depended on it. Which, by the way, they don’t. All they have to do is act like they can sting and that’s quite enough. The venom glands of many species still produce abdominal secretions, and those secretions are still used defensively, but not as venom injected into enemies through hardened stingers. Spatulate stingers are used by these ants and several other species of ants — who are also fitted with spatulate, rather than hardened needle-like stingers — to slather their venom on the bodies of their prey and their predators.
Now, what about the damage these ants cause to the wood and walls they nest in? It happens that they only nest in places that have already been damaged by wood-rot fungi or other insects (e.g., termites). They don’t damage sound wood or wallboard, but they do provide a good indication that some other problem (water infiltration and/or termite activity) is taking place at that location.
But what about their cultivation of homopteran organisms? Most acrobat ants feed primarily on the honeydew secretions of the homopteran scales, aphids, and mealybugs they cultivate in trees, shrubs, and other botanicals. Any good gardener worth his or her salt is dismayed to find evidence of homopteran incursions onto their garden plants because, once established, the damage done by these organisms is both extensive and difficult to control. Since acrobat ants work hard to disperse scale, aphids, and mealybugs, one might think the first thing a good gardener should do is to control these ants. Again, first impressions are not always best, as the following demonstrates:
“The cultivation of Homoptera by ants is usually considered detrimental to plants, but any damage may be offset by the ants’ predation on defoliators. Another factor that may contribute to the stability of the ant-Homoptera-plant relationship is the ability of some homopterans to withdreaw large quantities of sap without seriously injuring trees, thereby allowing them to feed on the same plant year after year (Bradley and Hinks 1968). A portion of the sap sustains the aphids, but most is passed on as honeydew to the ants. In return, the ants protect the aphids and the trees from their enemies.” (Hansen and Klotz 2005)
Ah, the pitfalls of unbridled intuition, particularly when we rely on its fruits without checking further. In my work with landscapers and gardeners I push for a balanced approach based on habitat modification that favor diversity over extermination. For homopteran control I release parasitic wasps that help keep their numbers in check, and that reduces the number of acrobat ants as well, without the necessity of exercising specific control measures on the acrobat ant populations themselves. The more organisms we have in our surroundings, the more likely it becomes that they will all work together, in a loose symbiosis that helps maintain a healthy ecosystem favorable to all. When that happens, everybody benefits.
- Kingdom Animalia (ahn-uh-MAYHL-yuh) — first described in 1758 by the Swedish taxonomist Carolus Linnaeus [23 May 1707 – 10 January 1778], using the Latin word animal = “a living being,” from the Latin word anima = “vital breath”, to refer to multicellular, eukaryotic organisms whose body plans become fixed during development, some of which undergo additional processes of metamorphosis later in their lives; most of which are motile, and thus exhibit spontaneous and independent movements; and all of whom are heterotrophs that feed by ingesting other organisms or their products;
- Phylum Arthropoda (ahr-THROPP-uh-duh) — first described in 1829 by the French zoologist Pierre André Latreille [November 20, 1762 – February 6, 1833], using the two Greek roots αρθρον (AR-thrawn) = jointed + ποδ (pawd) = foot, in an obvious reference to animals with jointed feet, but in the more narrow context of the invertebrates, which have segmented bodies as well as jointed appendages;
- Class Insecta (Linnaeus, 1758) — named using the Latin word insectum, a calque of the Greek word ἔντομον ( EN-toh-mawn) = “(that which is) cut into sections”; comprised of arthropods with chitinous external (exo-) skeletons, a three part body composed of a distinct head, thorax, and abdomen, the midmost part having three pairs of jointed legs, and the foremost part having a pair of compound eyes and antennae;
- Order Hymenoptera (hye-muhn-OPP-turr-uh) — first described in 1758 by the Swedish taxonomist Carl Linnaeus (1707 – 1778), who combined the Greek words ὑμήν (pron. humēn) = “membrane” + πτερόν (TARE-awn) = “wing”, thus ὑμενόπτερος (hew-men-OPP-tehr-ose) = “membrane-winged” to refer to insects with membranous wings, specifically the sawflies, wasps, bees, and ants; this is one of the largest orders of insects, and includes over 130,000 species;
- Family Formicidae (fohr-MISS-uh-dee) — first described in 1809 by the French zoologist Pierre André Latreille (1762 – 1833), from the Latin formica = “ant” to refer to hymenopteran insects that have elbowed antennae and a narrow waist that separates the thorax from the abdomen with a node-like petiole; at present, 20 distinct subfamilies of ants are recognized:
- Subfamily Aenictogitoninae: a subfamily comprising a single genus, Aenictogiton, with seven known species of rarely collected ants found in Central Africa with morphological and phylogenetic affinities to the army ant genus Dorylus; only males have been collected, and nothing is known about their workers, queens or behavior;
- Subfamily Agroecomyrmecinae: characterized by the following derived traits (see Bolton 2003): mandibular masticatory margins oppose at full closure but do not overlap; eye at extreme posterior apex of deep antennal scrobe; antennal sockets and frontal lobes strongly migrated laterally, far apart and close to lateral margins of head; abdominal segment IV with complete tergosternal fusion; sternite of abdominal segment IV reduced, tergite much larger than sternite and strongly vaulted;
- Subfamily Amblyoponinae (including the subfamily Apomyrminae): mostly specialized subterranean predators, comprised of a single genus of two species native to California; characterized by the following traits (see Bolton 2003): workers of this ant subfamily — which was formerly considered a tribe within the subfamily Ponerinae — exhibit the following characters: eyes small or absent, if present situated behind the mid-length of side of head; anterior margin of clypeus with specialized dentiform setae; the promesonotal suture is flexible; the petiole is broadly attached to abdominal segment 3 and is absent a distinct posterior face; the postpetiole is absent; a sting is present and is well developed.
- Subfamily Aneuretinae: this subfamily is comprised of a single extant tribe containing a single extant genus and a single extant species (several extinct tribes, genera, and species have also been described), namely the Sri Lankan relict ant (Aneuretus simoni); this is one of the few ant species considered endangered;
- Subfamily Cerapachyinae: a subfamily of 5 genera and 217 recognized species, distributed throughout the tropics; they possess spines on the pygidium; their antennae are short and thick; and they lack dorsal thoracic structures; they prey on other ant species;
- Subfamily Dolichoderinae: presently not divided into tribes, but comprised of 24 genera, including the Argentine ant (Linepithema humile), the erratic ant (Tapinoma erraticum), the odorous house ant (Tapinoma sessile), and cone ants in the genus Dorymyrmex; these ants are distinguished by having a single petiole, absent a post-petiole, and lacking a sting but possessing an apical slit-like orifice at the posterior abdomen instead of the round acidopore encircled by hairs typical of the Formicinae subfamily;
- Subfamily Ecitoninae (incl. “Dorylinae” and “Aenictinae”): New World and Old World army ants; in the New World, these ants are found in the tribes Cheliomyrmecini (containing the single genus Cheliomyrmex) and Ecitonini (containing the four genera Neivamyrmex, Nomamyrmex, Labidus, and Eciton); the genus Neivamyrmex — the largest of all army ant genera — contains more than 120 species, all native to the United States; the predominant species of the genus Eciton, E. burchellii, has been given the common name “army ant” and is considered the archetypal species; Old World army ants are usually divided into two tribes, Aenictini and Dorylini, but are often treated as a single tribe, Dorylini, alone; each contains a single genus; the genus Aenictus contains over 100 species, and the genus Doryus contains the aggressive “driver ants”, of which 70 species are known;
- Subfamily Ectatomminae: In North America a single genus, Gnamptogenys, is represented; that genus is not native to North America but has been introduced;
- Subfamily Formicinae: (fohr-mih-SEE-nee) — first described in 1836 by the French entomologist Amédée Louis Michel le Peletier, comte de Saint-Fargeau (1770 – 1845), usu. referred to as Lepeletier, from the Latin formica = “ant” to refer to a subfamily of ants whose evolutionary development is not as robust as most other subfamilies, e.g., they generally retain such primitive features as pupal cocoons, ocelli in workers, and a lesser tendency toward reduced palpal or antennal segmentation; all formicines have reduced stings and enlarged venom reservoirs, with a venom gland that is uniquely specialized to produce formic acid, and a one-segmented petiole having the form of a vertical scale;;
- Subfamily Heteroponerinae:
- Subfamily Leptanillinae: comprised of two tribes, the Anomalomyrmini (two genera, seven species) and Leptanillini (three genera, 41 species); within the tribe Leptanillini the larva provide their hemolymph as food to the queen through specialized processes on their prothorax and third abdominal segment; this behavior resembles that of the unrelated Adetomyrma, also called Dracula ants, which actually pierce their larvae to get at the body fluids; ants in the genera Leptanilla and Phaulomyrma are minute, yellow, blind, and subterranean;
- Subfamily Leptanilloidinae: 1 tribe, 3 genera, 15 species;
- Subfamily Martialinae: 1 genus containing a single species, Martialis heureka, discovered in 2000 from the Amazon rainforest near Manaus, Brazil, and placed as the sole member of a new subfamily (Martialinae); the generic name, which means “from Mars,” refers to its unusual “out-of-this-world” morphology; the species epithet heureka honors the surprise that accompanied its discovery; it is the oldest known extant species of ants;
- Subfamily Myrmeciinae (incl. “Nothomyrmeciinae”): once distributed worldwide but now restricted to Australia and New Caledonia; one of several ant subfamilies which possess gamergates, i.e., female worker ants which are able to mate and reproduce, thus sustaining the colony after the loss of the queen; formerly composed of a single genus, Myrmecia, but revised (Ward & Brady 2003) to include two tribes and four genera; three additional genera, one form genus, and nine species were later described (Archibald, Cover and Moreau 2006) from the Early Eocene of Denmark, Canada, and Washington;
- Subfamily Myrmicinae: approximately 130 genera in 23 tribes, and 10 additional genera not assigned to specific tribes, all cosmopolitan; the pupae lack cocoons; some species retain a functional sting; the petioles have two nodes; nests are permanent, in soil, rotting wood, under stones or in trees; the subfamily includes leaf cutters (tribe Attini), acrobat (tribe Crematogasterini), harvester (tribe Myrmicini), big-headed (tribe Pheidolini), and fire (tribe Solenopsidini) ants;
- Subfamily Paraponerinae: comprised of a single genus, Paraponera, containing a single species (Paraponera clavata), known as the lesser giant hunting ant, the conga ant, or the bullet ant (so named for its powerful sting); this ant inhabits lowland rainforest, from Nicaragua and eastern Honduras, and south to Paraguay; the ant is called “hormiga veinticuatro” by locals to refer to the 24 hours of pain following each sting;
- Subfamily Ponerinae: about 1,600 species in 28 extant genera, including Dinoponera gigantea, which is one of the largest species of ant found in the world; distinguished from other formicine subfamilies by their constricted abdomens;
- Subfamily Proceratiinae: similar to Ponerinae but the promesonotal suture is fused and the frontal lobes, elevated rather than transverse, are frequently reduced; antennal sockets are exposed in frontal view; in most species abdominal tergite 4 is much enlarged and vaulted, while abdominal sternite 4 is reduced; these are specialized predatory ants that are represented in California by a single species;
- Subfamily Pseudomyrmecinae: three genera of slender, wasp-like ants that forage alone and readily sting when molested;
- Subfamily Myrmicinae (murr-mih-SEE-nee) — approximately 130 genera in 23 tribes, and 10 additional genera not assigned to specific tribes, all cosmopolitan; the pupae lack cocoons; some species retain a functional sting; the petioles have two nodes; nests are permanent, in soil, rotting wood, under stones or in trees; the subfamily includes leaf cutters (tribe Attini), acrobat (tribe Crematogasterini), harvester (tribe Myrmicini), big-headed (tribe Pheidolini), and fire (tribe Solenopsidini) ants;
- Tribe Crematogastrini (crimm-ATT-oh-gass-TREE-nee);
- Genus Crematogaster (crimm-att-oh-GAS-tur) — first described in 1831 by the Danish paleontologist, zoologist, and archeologist Peter Wilhelm Lund (1801 – 1880), whose scientific work was concentrated in Brazil; he is considered the father of Brazilian paleontology and archeology; Lund apparently crafted the generic name using the Latin cremare = to burn, consume + the Greek root γαστηρ (GAS-tur) = stomach, in reference to the manner in which some species in this genus eject formic acid (mixed with other chemicals) through a spatulate stinger that then smears the burning liquid on their intended victims in the course of a defensive or offensive act.
- Blaimer, Bonnie B. 2012a. A Subgeneric Revision of Crematogaster and Discussion of Regional Species-groups (Hymenoptera: Formicidae). Zootaxa 3482:47-67
- Blaimer, Bonnie B. 2012b. Taxonomy and Species-groups of the Subgenus Crematogaster (Orthocrema) in the Malagasy region (Hymenoptera: Formicidae). Zookeys 199:23-70
- Bolton, Barry. 1994. Identification Guide to the Ant Genera of the World. Harvard University Press.
- Bolton, Barry. 2003. Synopsis and Classification of Formicidae. Memoirs of the American Entomological Institute, Vol. 71.
- Klotz, John H. and Laurel D. Hansen. 2008. Urban Ants of North America and Europe: Identification, Biology, and Management. Cornell University Press.
- Mallis, Arnold, Stoy Hedges (Ed.) et al. 2011. The Mallis Handbook of Pest Control, 10th Edition. The Mallis Handbook Company.
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