I have been thinking about ant antennae for awhile now. First, I became very interested in antennae because there are so many different forms in insects and also in ants. The form of antennae is a key characteristic in ant identification — how are they attached, how long are they, how many segments, is there a club or not, and if there is a club how many segments make up the club?
While the morphology is important to identification, this variety certainly raises functional questions. What are these differences about physiologically? Why are they important and what do they mean behaviorally?
Recently I have been raising more questions about antennal physiology and sensory perception because of my observations of interactions between individual Comanche harvester ants. I have been conducting nestmate discrimination tests between individual ants by introducing the ants in an arena and observing the ants’ behavior. While these interactions may vary, the antennae almost always have some role. Sometimes, it has been a brief touch or haphazard encounter but other times, the ants spend some seconds or longer facing each other and running their antennae over each other. This may or may not be accompanied by mandible gaping or gaster waging and the encounters may or may not develop. Mostly, the ants go their own way.
It is obvious that the antennae are more than chemosensory or smelling structures and this is well documented in many insects. Antennae may have sensory receptors for mechanical force, tactile stimuli, chemo-sensation, smell/taste, humidity, and air flow. This multiplicity of perception is a challenge to understand and to place in the context of behavior: what information does an ant get and how does she respond?
Also, the elbow shape of ant antennae make the antennae particularly mobile, rather like our arms. Perhaps, the sensory structure can be thought of, loosely, like our hands and fingers — very sensitive. Although ants don’t use their antennae to manipulate their environment as we use our hands, these structures are key to how the ants interact with their environment. That they have an antenna on each side of the head gives a kind of stereo view of the world — whatever sense they are using. I find this rather fascinating to think about: the stereo world of the ants along all these perceptual lines.
I wonder what these means for the behaviors I am observing. How much are they detecting just being in proximity to one another, how much if they have a bare encounter, and why do some of them spend many seconds using their antennae on one another and others do not? What can they detect, what do they pay attention to, and why are there such differences in responses? Context matters but there is more to this than context.
For the Comanche ant, these questions seem particularly important because they do not use trunk trails and have poor recruitment to resources, etc. which means that pheromones may not be so key to their communication as it is in other ant species. They seem to be rather visual in their orientation for foraging. So what is their perceptual world? I wonder.