Regional Director of Ensystex, Steve Broadbent, examines the ability of termites to ‘listen in’ on ants and other predators.
It is well documented that animals and plants sense their environment and communicate by means of chemical, visual, auditory and vibrational stimuli. Whilst such communications are usually directed to a specific target organism – the receiver – other organisms can ‘eavesdrop’ on these conversations. Communications intended for nestmates or partners might be intercepted by competitor species, parasites or predators, for the latter’s benefit.
Mäntylä showed how mountain birches when predated by insects, emit volatile chemicals to draw in predators that prey on these insects.1 Prey species can also eavesdrop on predator communications to reduce risks and avoid predation. Most professional pest managers are aware that ants are natural predators of termites, yet we often see ants in close proximity to termite workings. Fossil records show signs of ant attacks on termites going back over 100 million years, indicating this is a long-established predator/prey relationship.
The termites’ main defence against ants has been the development of mounds and mud galleries, which are designed to exclude ants. These structures are in turn guarded by the soldier caste. Yet termites cannot always isolate themselves from the outside world. Contact has to be made when seeking out new food sources. Whilst the termite’s soldier caste provides some protection, avoidance remains their preferred strategy. This suggests they might be able to intercept ant communications in order to steer clear of them.
When compared to ants, termites are more limited in their senses. Termite workers and soldiers are blind, so they need to use either chemical or vibrational cues to direct their behaviour. Certainly ants have a complex range of chemicals in their exoskeleton and are known to communicate with pheromones. Like all animals, ants also create vibrational signals from their movement.2 But what about termites?
Termites use vibrational sounds to detect the size of their food and the timber chewing sounds of other termite species, and thus avoid food competition. The classic example of this is shown by the ability of drywood termites (Cryptotermes spp.) to eavesdrop on more aggressive subterranean termites and avoid competing with them. It seems reasonable to consider that termites might use this ability to spy on ants too.
The idea that termites might spy on the vibrational cues of ants, was investigated by an Australian team of researchers working mostly with Coptotermes acinaciformis (pictured above) and the meat ant (Iridomyrmex purpureus).3 Their field work showed that, when they found ants and termites beneath the same timber monitors, they were always separated by a thin clay wall, usually no more than a few millimetres thick. In these situations, the meat ants only found their termite prey after they were disturbed by the researchers. This was indicative that termites were able to spy on the ants and avoid their presence.
Of interest was the observation that ant abundance did not affect the distribution of termites attacking the timber monitors, however there were statistically less earthworms present when the ants were abundant. It appears the termites were able to detect the presence of the ants and avoid them. Given the above observations of the termites building clay walls to separate themselves from the ants, the earthworms must have either fallen prey to the ants, or they were also able to detect the ants and escape the area. Both options would explain why fewer earthworms were present when ants were abundant. It is well documented that ants feed on earthworms, which is supportive of the predation option.
In laboratory choice experiments, it was evident that the termites displayed different behavioural characteristics, depending upon whether ants were present or not. This showed termites were able to detect the presence of ants. When ants were present, the termites either left a protective timber barrier in place, separating them from the ants, or they added a protective layer of clay to keep them separated. When ants were not present, the termites ate fully through the timber food sources.
Measuring the vibrations from ants and termites walking revealed that ants made significantly more noise than termites. The meat ants were about one-hundred times louder than the termites. For comparably sized insects, this 100-fold difference in the magnitude of the sounds made, was typical across the range of ant and termite species measured. Thus, even though the various ants and termites tested were of a similar size and showed similar levels of activity, the ants made significantly greater vibrational noise than the termites. In fact, the smallest ant (Lasius niger), caused similar vibrational noise to the largest termite tested (Mastotermes darwiniensis), even though the Mastotermes worker was ten times larger than a L. niger worker.
All pest managers would be aware of the alarm signals of soldier termites. When they feel threatened, the soldiers will either audibly bang their heads on the timber substrate or shake their bodies. A comparison of the walking sounds created by the meat ants showed that it was of similar amplitude and peaks as the head banging sounds of termites, at 19 Hz. This perhaps suggests that the soldier’s head banging sound evolved to mimic the ants walking sound, as an early warning signal.
We are clearly observing the termite prey species listening in on the vibrational sounds caused by the predatory ants walking, and then using this information to hide from the ants. The fact that the termites also created significantly less vibrational noise than the ants might further indicate that the termites ‘keep quiet’ in order not to reveal their presence to marauding ants. The use of visual camouflage by animals, to either hide from predators, or by predators to conceal their presence from their prey species, is well known. It appears the termites might similarly be camouflaging their presence acoustically.
In field trials, the success of the termites’ strategy was evident from the termites foraging in close proximity to their ant predators, albeit protected by a timber or clay wall. Whilst this is a risky and high-energy strategy, involving the construction of reinforced clay barriers, it offers benefits in the discovery of new food sources. Since termites largely communicate through vibrational sounds, it is logical that this ability would evolve as a mechanism to protect them from ants, by listening in on the ants walking sounds.
Steve Broadbent, Regional Director, Ensystex
1 Mäntylä, E., Klemola, T. & Haukioja, E. (2004). Attraction of willow warblers to sawfly-damaged mountain birches: novel function of inducible plant defences? Ecol. Lett., 7, 915–918.
2 Cocroft, R.B., Gogala, M., Hill, P.S.M. & Wessel, A.W. (eds.) (2014). Studying Vibrational Communication. Springer-Verlag, Berlin-Heidelberg.
3 Oberst, S., Bann, G., Lai, J.C.S., & Evans, T.A. (2017). Cryptic termites avoid predatory ants by eavesdropping on vibrational cues from their footsteps. Ecol. Lett., 20, 212–221.