What do arboreal ants eat? This is not such an easy question to answer as one might think. Nitrogen, vital for building proteins, is typically in short supply in the tops of trees. Ants as a group are often viewed as scavengers, getting nitrogen from dead arthropods that they find in the environment. But dead arthropods in the canopy will tend to fall, or be blown, to the ground.
So where do arboreal ants get the nitrogen they need to build their colonies? One important source is the trees themselves. Arboreal ants drink nitrogen-poor but extremely abundant plant sap by tending sap-sucking insects. In essence, the ants use the bugs as drinking straws, and some groups can be seen as herbivores in terms of the source of much of the nitrogen they acquire.
But are there other nitrogen-rich snacks in the canopy that ants rely on? The answer, at least for Cephalotes, would seem to be yes. Cephalotes just love to eat bird droppings. In fact, a nice fresh dropping will elicit stronger recruitment than any other food source. They also love leaves that have freshly deposited urine on them, from arboreal mammals. Although these sources of vertebrate waste most likely have less than ideal forms of nitrogen, Cephalotes have a gut packed full of microorganims that may well help is converting it to something useful.
The fun part of Cephalotes’ affinity for this unusual resource, however, is that it makes for a very convenient and highly effective “natural” bait. I have now switched exclusively to urine baits harvested from, er, a bipedal cerrado primate in my work with Cephalotes. Aside from being free and unlimited (as long as the primate(s) in question have a good water supply), it is more effective than traditional baits, like sardines. For those interested in behavior, like me, it is also a natural food resource for this group and therefore invaluable in studying natural foraging and recruitment behaviors (ants don’t tend to find many naturally occurring sources of fish protein on the canopy). Moreover, it makes for good photographs, by pulling a large number of ants from nearby nests and becoming invisible once the water has evaporated off. It turns out that this food is also highly attractive to many other groups of arboreal ants. This is intriguing from a scientific standpoint, but also very useful for any myrmecologist interested in finding and photographing some nice arboreal ants. Something to keep in mind next time you are all in the field and nature calls.