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My favorite genera of ants

May 11, 2011
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Ants are not smarter than humans (even the ones that are good at path integrals).  Nonetheless, the list of their cultural and technological “inventions” is pretty impressive.

Consider, for example, the following abbreviated list of things that were invented by ants long before they were invented by humans:

That’s quite a list for an animal with a brain 340,000 times smaller than a human’s.  And that’s to say nothing of the things that ants can do that we can’t, like make bridges and shelters by linking their bodies together.

Today, for no particular reason, I feel like extolling the wonders (and/or horrors) of the formicidae family.  I’ll do so by listing a few of my favorite ant genera (which, as I learned only fairly recently, is the plural of “genus”), along with pictures and brief description of the advanced things they do. I hope to leave you with the beautiful sense that ants have fully-formed civilizations and economies of their own, and that it is by no means a stretch to compare them with those of humans.

My guide in this whimsical exercise will be the fairly incredible book Ants of North America: A Guide to the Genera, which was an excellent birthday present a few years ago.  Quotes and images below come from that book.  And, of course, I use plenty of Wikipedia.

If there are any entomologists that happen across this blog post, I would be glad for your comments/corrections.

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Atta: fungus growers

Atta Mexicana

Ants from the genus Atta are farmers.  For some reason it had never occurred to me that ants could farm, even though I had spent many childhood hours watching leaf-cutter ants carry away chopped up pieces of plants and I must have realized that ants probably can’t eat leaves.

In fact, those ants were carrying away the leaf fragments to use them as fertilizer for their vast, underground fungus gardens.  In these gardens the ants cultivate various species of fungus for food, carefully keeping them free of pests and molds.  This is agriculture on an enormous scale: Atta live in giant colonies of millions of individuals and have an intricate division of labor maintaining their economy.

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Pyramica: Benefitters of the Farming Economy

Pyramica creightoni

The enormous economic output from the huge farming colonies of Atta (and the similarly agricultural genera Acromyrmex and Trachymyrmex) creates opportunities for more humble, specialized genera like Pyramica.

Ants in the Pyramica genus are specialized predators of little flea-like bugs called Collembola, or “springtails”.  Collembola are a prevalent parasite in the fungus colonies of growers like Atta: they eat the fertilizer that the ants have collected.  So the Pyramica perform a service for their farming neighbors by hunting the Collembola through the fungus gardens.  Pyramica also benefit from the carefully climate-controlled environment that Atta maintain in their fungus gardens.

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Nomamyrmex: Specialized predators of Atta

Nomamyrmex esenbeckii

One of the striking things about ants is that they seem to fill every economic niche that one could imagine.  Every time there is an opportunity for a living to be made in the insect world, ants find a way to exploit that opportunity.

Nomamyrex is a great example.  These are specialized predators of the workers in the enormous Atta colonies.  They’re not much bigger than Atta, but they are heavily armored with powerful mandibles.  They hunt underground in orderly battalions that are said to “resemble a Panzer division on the march.”

[Update: Apparently, when you hunt Atta, you've got to be very careful.]

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Labidus: Underground hunters

Labidus coecus

Ants that live underground have little use for eyes.  So it is with Labidus, a genus of mostly subterranean army ants with powerful, barrel-shaped heads and no vision whatsoever.  Labidus ants live in enormous colonies and make their living by sweeping through underground tunnels searching for bugs, worms, and whatever else they come across.

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Prenolepsis: “Human food storage”

Prenolepsis imparis

Prenolepsis ants are the ultimate foragers.  They are hardy ants that live comfortably from California to Mexico, and are known for their ability to forage even in very cold temperatures.  They also have the ability to store fat in their own enormously bloated abdomens and regurgitate it to feed others when the colony becomes dormant during the hot summer.

This is similar to the behavior of the more famous “honeypot ants” of Australia and the deserts of North America.

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Crematogaster: Livetock tenders

Crematogaster lineolata

Agriculture in the ant world does not stop at fungus tending.  A number of ant genera, including Crematogaster, tend aphids and coccids as livestock.  Most of the time, the ants are essentially dairy farmers: they protect the aphids in exchange for a syrupy secretion from the aphids called “honeydew”.  The ants even have a way of “milking” the aphids by tapping the aphids on the back with their antenna to get them to secrete.

The ants can have other relationships with their livestock as well.  Sometimes they play the role of poultry farmers, tending the aphids and collecting their eggs for food.  Other times they simply eat the aphids.

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Anergates: identity thieves

Anergates atratulus

One way to make a living in the world is by hard work and industry.  Another way is to steal from somebody else.

The genus Anergates is, apparently, poorly equipped to make a living.  There are no workers, individuals are relatively puny, and the males of the genus are so helpless that they are described as “pupoidal — yellow to cream in color, wingless, and barely able to walk.”

Since there are no members of Anergates capable of procuring food, the females can only survive by invading the nests of other species, killing the queen, and then posing as the queen and being waited on by the other members of the host colony.  In fact, Anergates has a preferred target for this identity theft: the species Tetramorium caespitum.  Apparently no other ant species is weak enough to be susceptible to this one-ant invasion.  It is said that “the best way to collect Anergates is to remove the queen from a T. caespitum colony in the spring and come back the following year”.

Ironically, since the new Anergates faux-queen is unable to produce any new workers, she can only survive as long as the youngest workers in the host colony.  Eventually the colony dies out due to a lack of reproduction, and then the Anergates female dies out as well.

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Formica: Slavers and Slaves

Formica (sanguinea group) gynocrates

It was pretty shocking to me to learn that humans were not the original inventors of slavery.  The ants of the Formica genus apparently have a varied range of slave-making behaviors.  Ants of the sanguinea group, for example, raid the colonies of other Formica groups, carrying off some of their members for labor in the sanguinea‘s own colonies.

Sometimes adult workers are taken captive, and other times the slave raids are more violent: all adults in the colony are killed and only the developing pupae are carried away into a life of subjugation to their captors.

Some Formica groups can enslave multiple other groups of ants, but Formica sanguinea has a particular target: the Formica pallidefulva group:

Formica (pallidefulva group) dolosa

The Formica pallidefulva group are omnivorous foraging ants who live in relatively small colonies (in the ant world, a few thousand counts as small).  Unfortunately, they spend much of their lives enslaved by the slightly larger sanguinea group.

Of course, enslaved ants aren’t always docile.  In recent years entomologists have documented cases of violent slave uprisings conducted by slave ants that were abducted as pupae.  Here’s one summary of this incredible finding.

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Cephalotes and Camponotus colobopsis: Plugheads

Camponotus (colobopsis group) obliquus

These genera of ants are so strange, you almost have to see them to believe it.  They live exclusively in trees, digging nests for themselves in hollow branches or sticks.  Since they are relatively small and few in number, they have developed a unique form of defense.  Namely, they have large, flat, plug-shaped heads that they use to block the entries to the nest.  When some foreign danger presents itself, the soldier caste quickly mobilizes to block all entries against intruders, like this.

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Bonus — Discothyrea: ???

Discothyrea testacea

Just so you don’t leave thinking that all the mysteries of the ant family are solved, I’ll leave you with one of the strangest genera of all.  This is Discothyrea, a tiny ant described as “like nothing else in the solar system”.  It has weak, toothless mandibles, useless vestigial eyes, and very strangely-shaped antennae.  It has been collected in rotten logs and in hummus, but almost nothing is known about how it lives.

At a recent concert I attended (in a tiny, campy theater in Wisconsin), the great guitarist (and ant enthusiast) Leo Kottke quipped that Discothyrea must survive by confusing potential attackers with its smooth, featureless knob of a head.  “Some ants survive by attacking and some survive by hiding.  This one seems to survive by suddenly appearing and posing an existential question.”  [Kottke then went on to play the song "Disco", and I finally understood why the song sounded nothing at all like disco music.]

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In summary, ants are awesome.

In lieu of a more intelligent conclusion than that, let me leave you with my favorite ant-themed song of all time.

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