Eciton hamatum workers return from an afternoon raid bearing mouthfuls of pilfered ant brood (Ecuador)

Meet Eciton hamatum.

This is a delightfully orange-colored army ant from Neotropical rain forests, big and charismatic, like the iconic E. burchellii. But- and here’s a secret trick of the wiley nature photographer- it is a much friendlier insect. If you’ve got an assignment to shoot army ants and your editor neglects to specify the species, I’d hold out for these guys. You won’t get swarmed over, gored, bitten, stung up, or otherwise assaulted anywhere near the amount you suffer by approaching the vicious E. burchellii.

This raiding party has gotten into a bee nest, as evidenced by the large bee pupa at right. Note that it takes two ants to carry such a heavy burden.

Eciton hamatum is a more typical army ant in its dietary preferences. It targets social insects, especially bees, wasps, and ants.

A media worker carries a captured male ant

Since E. hamatum‘s prey inhabits discrete nests the food landscape for this species is mostly empty, punctuated by isolated spots of great bounty. Thus, the raid strategy is correspondingly different from that of the generalist E. burchellii.

decpiction of an Eciton hamatum column raid, from Rettenmeyer (1963)

Raid fronts concentrate workers into a number of exploratory columns, each with enough ants to bring immediate pressure onto any prey colony they encounter. These dense columns are important because prey aren’t naive. When facing army ants,  targeted colonies evacuate quickly!

From above, a raid looks like the figure at left. Tendrils fan out from a central trail over the forest floor. Columns stay tight enough that when an ant or wasp nest is located enough workers are around to effectively exploit the discovery. Unproductive tendrils are abandoned, and their raiding parties rejoin the central trail.

As for E. burchellii, raids start from the bivouac in the morning and spread outward for tens to hundreds of meters during the day. The back end of the raids consolidate into a smaller number of support and food transport trails.

An ant nest in the leaf litter (indicated by piles of excavated soil) is discovered by a raiding party.

The soldier caste of Eciton hamatum is similar to that of E. burchellii, bearing the same defensive tusks. Eciton hamatum soldiers, though, have a much larger set of horns along the back corners of the head. These protrusions presumably protect the ant’s vulnerable neck in fights with other ants, and this species certainly spends a great deal more time fighting other ants than does E. burchellii.

Eciton hamatum soldier

On a personal note, I found photographing this species to be great fun. Most of my Eciton encounters over the years have been with E. burchellii or E. vagans. In comparison, E. hamatum is charming. Their physique is a bit more pudgy, they are an unusual shade of orange, and they are much less aggressive. The effect is almost comical.