A guide to common ants of the Amazon rainforest

Ectatomma tuberculatum (Colombia)

Tourists flock to Amazonian jungle lodges hoping to find monkeys, toucans, and jaguars, but most of the animals they see are insects. Especially, ants. The Amazon region contains more than 1,000 species, many still formally undescribed, and they basically run the place. The leafcutter ants and their fungi are the forest’s premiere herbivores, the army ants are an ever-present apex predator, the others are scavengers, soil-churners, predators, and partners in the defense of numerous jungle plants. The jungle without ants would be a different, depauperate place.

Because every rainforest adventurer encounters ants, and because no decent guides exist to help general naturalists identify the more common species, I have created the following bestiary of Amazonian ants. I do not- and cannot- illustrate all those that occur in the region. I can, however, cover the formicids most likely to be noticed by a casual visitor.  (more…)

A heavy load

An ambitious Cyphomyrmex forager carries a piece of insect frass back to the nest. These ants feed exclusively on a fungus that grows on the bits of detritus they gather. (Mindo, Ecuador).

photo details:
Canon MP-E 65mm 1-5x lens on a Canon EOS 7D
ISO 100, f/13, 1/250 sec, diffuse twin flash

Dolichoderus rugosus

One of the largest ants in the Amazon basin:

Dolichoderus rugosus (Jatun Sacha Reserve, Ecuador)

photo details:
Canon EF 100mm f/2.8 macro lens on a Canon EOS 7D
ISO 200, f/16, 1/250 sec, diffuse overhead flash

The First Annual Accidental Bug Blogging Conference, Ecuador 2011

Bug bloggers are not exactly a large community. If I were optimistic I’d say that there are 100 of us around the world. Maybe. So it’s not as though I expect to run into another bug blogger in any given random place.

Random, say, like an Ecuadorian cloud forest:

Brigette Zacharczenko & Alex at the Yanayacu field station

While Mrs. Myrmecos and I were travelling about collecting Linepithema in rural Ecuador this January, we stopped in at the Yanayacu biological station for lunch. While there, we were engaged in conversation by a rather enthusiastic young woman positively ecstatic to be entomologizing in the tropics.

She looked somehow familiar, but I couldn’t figure out why. She’s a bit quicker than I, though, and pieced together enough dots to suddenly realize that we were both world-famous bug bloggers. It was Weird Bug Lady! You probably know her as the artist behind this adorable menagerie of plush arthropods.

The reason I mention this is that Brigette has just started a charming new blog on caterpillars. Go read.

Dolichoderus attelaboides: the long-necked ant of the Amazon

Dolichoderus attelaboides

I give numerous reasons for why I like ants, but chief among them is my fascination with just how many ways there are to be an ant. Taxonomists have formally named some 13,000 ant species and expect to discover at least another 5,000 or so. There are ants smaller than the head of a pin and ants larger than my thumb. Their societies may number several million, or just half a dozen. Some ants glisten like polished metal, others are furrier than a woolly bear. Some farm, some hunt, some scavenge. Some glide from tropical treetops, some swim in pitcher plants.

Distribution of D. attelaboides (modified from MacKay 1993).

One unusual species I was happy to encounter in Ecuador this January was Dolichoderus attelaboides. This is an ant that never outgrew its awkward adolescent physique. Dolichoderus attelaboides is more gangly than an ant should be, its limbs slightly too long. Its eyes boggle from a head supported by a false neck too thin for its size.

Dolichoderus attelaboides is a common insect in lowland South American forests. It is one of the larger species you might find wandering about in the undergrowth of a tropical rain forest. Yet like most tropical ants, little is known of its biology, and nothing is known about why it has evolved such a charmingly clumsy form.

Like most members of its subfamily (Dolichoderinae), D. attelaboides often tends hemipterous insects for honeydew. And like most members of its genus, it sports a rough, armored exoskeleton.

I will venture my own hypothesis for the strange appearance of this ant, however. I suspect the shape helps Dolichoderus attelaboides escape dismemberment by Eciton army ants.

When ants fight each other, the highest incidence of physical damage is body parts severed at their weak points, the junctions between the hardened plates. Heads detach most easily when cut at the neck, for example. If we look at the two points of unusually narrow constriction on the body of D. attelaboides– partway along the ant’s pseudo-neck and in the middle of the mesothorax- we’ll see they are adjascent to more vulnerable sutures. Any large ant attempting to bite a D. attelaboides will find their mandibles settling into grooves in the middle of armored plates rather than the membranous tissue between them. Essentially, they are false joints. The remaining vulnerability- the waist- is protected by a set of spines.

Most species of Eciton are predators of other ant species. Dolichoderus attelaboides is a sizable ant living in large colonies- a great source of protein for army ants if the colony’s defenses could be breached. Given that both ants are common in the same habitats, and that the size of both ants is similar, I think it entirely reasonable that the gawky pencil-neck form and heavy armor of D. attelaboides is a response to the army ant threat.

Of course, this is speculation. Someone will have to feed dozens of Dolichoderus workers to army ants to test whether the predators’ mandibles actually land in the false joints, and whether those joints provide any real protection from bites.

source: MacKay, W.P. 1993b. A review of the New World ants of the genus Dolichoderus. Sociobiology 22: 1-148. [(31.xii).1993.]

The other weaver ants

A Camponotus worker stands guard over her leaf nest.

Say “Weaver Ant” to an ant enthusiast and I guarantee you most will imagine the charismatic genus Oecophylla from tropical Africa, Asia, and Australia. Even wikipedia would agree.

But the American tropics also has weaver ants. Several species, in fact.

Wikipedia’s muddled definition aside, weavers are tree-dwelling ants that bind living leaves together with larval silk. These structures remain cool and humid, a perfect refuge from the tropical heat. As weaver ants are defined by behavior, and since the behavior has evolved repeatedly among ants, this is not a taxonomic grouping but a functional one.

During our recent Ecuador excursion we encountered one of the lesser-known weavers. Here’s a nest:

This species is in the genus Camponotus, a group best known for the pesty carpenter ants.

When the nest is disturbed, guards rush out with their gasters facing forward and ready to shoot a stream of formic acid at the intruder. This less-than-endearing habit makes them unpleasant photographic subjects. I had to clean acid off my lenses after taking these shots.

I bring all this up as a suggestion for aspiring myrmecologists. Weaving behavior has evolved enough times to form a replicated natural experiment. Because there are so many separate inventions of weaving (at least 5 or 6), statistical techniques can be used to infer the characteristics that predispose lineages to evolving a weaving lifestyle. If you are looking for a good ant evolution project, say, the sort of work one might do for a Ph.D. dissertation, this topic is ripe for the picking.

photo details:
(top, bottom) Canon 100mm f/2.8 macro lens on a Canon EOS 7D
ISO 200, f/13-14, 1/200 sec exposure, indirect strobe
(middle)Tamron 11-18mm wide-angle zoom on a Canon EOS 7D
ISO 200, f/9, 1/250 sec, hand-held fill flash.

Social Spiders

Sometimes I’m glad not to be a grasshopper:

Anelosimus sp. social spiders (Ecuador)

Nothing freaks out the arachnophobe in me more than social spiders. One of the more common arachnids in tropical forests, these spiders spin communal webs with hundreds or thousands of individuals.

Anelosimus, up close

photo details:
Canon EF 100mm f/2.8 macro lens
Canon EOS 7D
(top) ISO 400 f/11 1/250 sec
(bottom) ISO 200 f/14 1/250 sec
off-camera strobe

(middle)Tamron 11-18mm wide angle zoom
ISO 800 f/7 1/25 sec

The Amazing Inga

A carpenter ant feeds from an Inga leaf nectary (Ecuador)

The genus Inga contains hundreds of woody plant species in the American tropics, from tall canopy trees to diminutive understory shrubs. All species sport cup-like nectaries on their leaves, presumably an offering to ants whose presence dissuades herbivores.

Because Inga hosts a reliable entourage of happily sedentary ants, its nectaries are perhaps the easiest place in the rain forest to photograph the normally frenetic insects. Here are some recent shots from Ecuador.

Ectatomma ruidum
Pheidole sp. minor workers
Linepithema tsachila

(Incidentally, Linepithema tsachila is one of the species I described as part of my doctoral dissertation- always good to see an old friend!)