Excerpts from Jim Conrad's
Naturalist Newsletter

from the March 31, 2008 Newsletter issued from Mexico's Southernmost State, CHIAPAS

Wednesday night as I sought my sleeping spot in the reserve I came upon a black, seething mass of army ants. I've told about army ants before, but then I had no camera. Now you can see what I saw that night below:


What's missing in the picture is the movement. The whole mass of ants, which was about the size of a large kitchen table, constantly changed its shape like an amoeba and consisted of several ant streams, some streams flowing in directions contrary to the others. Here and there black knots of ants coagulated and melted away in just seconds, and I figured that these represented "false alarms," something having triggered an attack, but then there was nothing. Though individual ants moved fast, the movement of the whole ant mass was slow, at that time seeming indecisive about which way to go. To get the picture I held the camera as far away from my body as I could, but still a few soldiers on the perimeter climbed my legs and bit.

Basically the idea behind army ants is that as a colony moves across the landscape it stirs up small animals, especially insects, a few of whom always escape in the wrong direction and then the ants quickly dismember them. I've read that army ants have been known to consume animals as large as goats but the largest animal I've ever seen them tear apart was a grasshopper, which disappeared chillingly fast.

In the picture you can see at least two ant sizes. Note how the larger ants usually appear at stream edges. It looks like they're keeping the smaller ants from wandering away from their streams, but who knows?

from the October 3,  2010 Newsletter issued from Hacienda Chichen Resort beside Chichén Itzá Ruins, central Yucatán, MÉXICO

All week a battalion of army ants has circulated in the area and it hasn't been easy on my ankles. Usually I don't realize I've wandered into their seething black currents moving across the ground until they've started biting, and then they hold on until they're picked off. We've met army ants here often enough, but what's new this time is that I remembered that my dandy little digital camera has video capabilities, so I filmed this week's invasion streaming across a portion of ground. Maybe you can see that below.

Luis who produces the milpa, or traditional cornfield, told me what he watched them do. A big wave of them crossed his milpa one morning, climbed two or three big Piich trees and found nothing, but then high up another Piich they found a big cavity holding a colony of Africanized Bees -- "Killer Bees," as the press calls them. The ants immediately set about cutting the bees to pieces.

"They'd walk up to a bee and with their big jaws cut the bee right across the midsection. The bee's parts fell to the ground, where other ants were waiting to carry them away. Beneath the tree it was like a dry rain falling, but it was pieces of honeybees. Those ants wiped out the whole colony, then ate the honey, left, and didn't come back.

from the January 16,  2005 Newsletter issued from Komchén de Los Pájaros near Telchac Pueblo, western Yucatán, MÉXICO

The other morning I was weeding the lettuce when gradually it dawned on me that over to my right the ground was moving. It was an advancing front of army ants and I didn't have much choice other than to turn the lettuce patch over to them.

Unlike the leafcutter ants I told you about earlier, which can carry away every bit of leaf and flower material in a tree or garden, army ants are carnivorous, not vegetarian, so my lettuce was safe. As the ant-front advanced I watched as worker ants fastidiously searched beneath every lettuce leaf, in every crevice in the ground, and around the corner of every stem. Any small animal that couldn't get away was doomed. I've read that army ants can dismember and devour animals as large as goats, but the largest thing I've ever seen them tear apart was a grasshopper. And you should see the grasshoppers springing from the grass as a wave of ants moves through it.

The site at www.insecta-inspecta.com/ants/army/ says that when army ants rest, or "bivouac," they form tunnel- and chamber-containing nests from nothing but their own bodies. They do this by fastening onto one another with their mandibles (jaws) and claws. The site also says that army ants, though possessing simple eyes, are blind.

The blindness doesn't seem to hinder them at all. In fact, as you witness their amazing degree of organization and cooperation, it's easy to believe that they may have senses, or experience a sophisticated manner of being, we humans can't even imagine. You might be interested in reading about the idea that ant colonies may possess a "collective intelligence" at www.knowledge.co.uk/frontiers/sf066/sf066b07.htm.

The first-mentioned website also claims that army ants work at night. I have often seen them working during the day, as on my lettuce-weeding day. That site is focusing on just one species. A site on New World Army Ants at www.armyants.org/indexfiles/speciesindex.html lists 45 army-ant species in Costa Rica and we probably have that many or more here in Mexico.

Once I spent a summer living next to a family in the Nahuatl-speaking country of eastern San Luis Potosí, in east-central Mexico. That family by no means suffered Alfred Hitchcock moments when army ants invaded their house. In fact, they seemed to rather like it.

First, it meant that they could abandon the day's chores, go sit in the park, and if someone asked them why they were being so lazy in the middle of the day they could just say "ants" and everyone would understand.

Second, army ants do a great job cleaning houses of scorpions.

from the February 13,  2005 Newsletter issued from Komchén de Los Pájaros near Telchac Pueblo, western Yucatán, MÉXICO

Approaching Komchén's main living area on Monday morning I found a bit of commotion. A dark smudge of army ants was swarming across the shop's walkway into the bushes before the library. Ana María and Lino were on hand and I heard Ana María exclaim "Pobrecita" ("Poor little thing...") as she rushed to the ant- smudge front and scooped something into her bare hands.

She'd saved a mature tarantula somewhat larger than the top of a coffee cup. It was a black one with long, stiff, red-orange hairs mantling her abdomen. The creature had been chased from her nest by the ants and at that point 20-30 ants were still on her, tearing at her body. Ana María carried her to a quiet spot, put her down, and set about squirting water on the ants, trying to redirect them away from where guests were sleeping.

The tarantula remained where Ana María placed her for at least 20 minutes, moving not at all as the ants continued trying to dismantle her. However, the ants couldn't get past the creature's stiff, sharp hairs. The ants did manage to cut two small bunches of hairs from her, fashion them into rough balls, and begin moving the hair-balls through the grass.

However, now those ants had been separated from the main ant swarm and were receiving no chemical instructions from their peers, so they really had no idea where to go with their booty. Eventually they just wandered off individually, directionless. As the tarantula found herself more and more free of ants she began twitching her legs, clearly getting ready to move on. Sad for her, even if she could find her nest again, her babies had surely been cut to pieces and carried off by the ants.

So, that morning, both army ants and tarantula had had their lives drastically rearranged. Ana María had interviened on behalf of the tarantula, but I had just stood there watching, feeling equally allied to ants and tarantula.

One other thing -- as the army ants continued advancing through the herbage, some Hooded Warblers and Ovenbirds overwintering here from North America appearead to be having some fun. They fed on many small insects abandoning their hiding places as they tried to escape the ant hoards

from the April 4,  2010 Newsletter issued from Hacienda Chichen Resort beside Chichén Itzá Ruins, central Yucatán, MÉXICO

The other day I was on my hands and knees watching a stream of army ants pass beneath me when this thought came to me: Sometimes when I've been in really anty situations I've smelled the ants' formic acid. If I should very gingerly smell this surging river of ants, would it smell like that?

I put my nose as close as I dared, sniffed, and smelled cinnamon.

I sniffed several areas nearby and smelled no cinnamon. I went to other parts of the ant stream and once again smelled cinnamon.

I've never heard of ants smelling like cinnamon. Has anyone out there?

We've seen streams of army ants before, but if you want to see a tiny part of one of this week's fast-moving, cinnamon-smelling streams passing over a rock, below:

army ants

from the October 16, 2011 Newsletter issued from Mayan Beach Garden Inn 20 kms north of Mahahual, Quintana Roo, México

The other day on the white sand road I biked upon a battalion of them streaming across the road in three or four lines that merged and separated from one another like intersecting superhighways. You can see them, flowing from right to left, below:

army ants crosing road

from the November 6, 2011 Newsletter with material from Mayan Beach Garden Inn 20 kms north of Mahahual, Quintana Roo, México

Sometimes army ants move en masse, as seen on the white sand road last Sunday near Mayan Beach Garden, shown below:

army ants moving en masse

That ant-blob was about the size of a large car with most but not all ants moving from right to left. My impression is that the same army-ant species sometimes moves in lines, sometimes in broad waves. Moving in a few narrow lines seems to be the quickest and safest way for them to get around, but moving en masse they are more likely to stir up insects such as grasshoppers who jump from one place to escape the ants only to land in the midst

from the August 21, 2016 Newsletter issued from Hacienda Chichen Resort beside Chichén Itzá Ruins, central Yucatán MÉXICO

Tuesday as I worked in the hut at the computer, something began biting on my ankle. It was a burning, pricking feeling that vanished soon after I brushed away whatever it was causing it. While I was bent over scratching the bite, from the corner of my eye I noticed that the hut's pole wall next to my head somehow seemed to be fluttering or oscillating. When I reared back and looked, I saw that once again army ants were sweeping through. Below, you can see a small part of the hut's interior wall, where the tops of the wall poles meet the thatch roof, with ants swarming into nooks and crannies looking for prey such as spiders and scorpions:

army ants on hut wall

Having run into army ants many times, we've put together a pretty good page on them, at http://www.backyardnature.net/mexnat/armyant.htm

However, we've never tried to identify them, so this week I've been looking at them taxonomically. In preparation for the task I took many close-ups, but it was hard getting clear pictures, since they were moving fast and I wasn't about to kill one just so I could take its picture. Still, the images show the ants' general form. Below, you can see a scurrying worker:

cf NEIVAMYRMEX CORNUTUS, worker from side

A worker photographed from above is shown below:

cf NEIVAMYRMEX CORNUTUS, worker from aboe

That image proved to be the most important one, for it shows that the back of the head is affixed with low, backward-pointing projections, that the end segment (abdomen) is hardly bigger than the head, and that the chest area (thorax) is broadest at its middle, gradually diminishing toward the head, which it joins with a narrow neck. The narrowed thorax front is unusual among army ant species.

At the edge of one ant stream a much larger ant seemed sick or confused, not moving as fast. This larger ant possessed substantial "pincers," or mandibles, and a much broader head to accommodate muscles to enable the mandibles to bite down hard, for this was a soldier, shown below:


Wikipedia's Army Ant Page does a good job introducing the subject. There we learn that over 200 ant species are considered to be army ants, but that different ant groups have independently evolved the roving, base-shifting behavior that qualifies a species as an army ant -- convergent evolution.

Learning that most New World army ants belong to the ant subfamily Ecitoninae, a Google search was made for research papers on Mexican Ecitoninae. This turned up the 2004 paper "Las hormigas Ecitoninae (Hymenoptera: Formicidae) de Morelos, México," by Quiroz-Robledo and Valenzuela-González, freely downloadable at http://www.antwiki.org/wiki/images/5/55/Quiroz_%26_Valenzuela_2004.pdf

Mainly using that paper's line drawings of worker ant outlines as seen from above, and noting especially the backward-pointing projections at the back of the head, and the narrowed forward part of the thorax, the best match for the species was NEIVAMYRMEX CORNUTUS

That paper was based on work done in the south-central Mexican state of Morelos, and there's a good possibility that here in the Yucatan we have other army ant species. Neivamyrmex cornutus is endemic just to Mexico. In Morelos the investigators saw the species preying on a termite colony, and in turn saw spiny lizards preying on the ants.

Despite the uncertainty, here we'll file this page on the Internet under Neivamyrmex cornutus, knowing that someday other researchers will confirm or correct the ID, and be happy to see the pictures and read about the species that visited a hut in the Yucatan, and spent most of the day streaming here and there in the hut's backyard.