The Chemical Arms-Race between Predatory Ants and their Termite Prey
Ants and termites have been locked in a vicious battle that has spanned millions of years. These eusocial insects have for generations been trying to gain the upper hand in this adversarial relationship through the evolution of physical and chemical weaponry with which to become victorious. Ants are one of the most successful groups of animals which have ever lived, and account for 15-20% of terrestrial animal biomass (1.). They are of the family Formicidae in the insect order Hymenoptera. Ants are voracious predators of invertebrates and over millennia have developed various means with which to incapacitate their prey. Termites are another highly successful insect group, in the infraorder Isoptera. One of the few animals capable of digesting cellulose (thanks to symbiotic bacteria found in their gut), termites can live in colonies ranging from a few hundred individuals to several million. This success has attracted unwanted attention from the termites primary predator, the ants, and as such have been forced into a chemical arms-race in order to survive.
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The first and fore-most chemical defence termites use when their colony is under attack by ants are alarm pheromones so the colony can brace itself. These substances are released from the frontal gland of excited soldiers. The frontal gland is a “huge sac-like organ extending from the ventro-posterior part of the head to the fifth or sixth abdominal segment” (2.) but varies anatomically between castes (soldier, worker, queen etc) and species, and is important in their chemical communication. These alarm calls are picked up by the antennae of other termites triggering their response. Response to the alarm pheromones are caste specific, soldiers tend to be attracted to the alarm and will release further pheromones upon arrival, amplifying the alarm. (3.) In most species, the workers will flee from the alarm, or will not respond at all. In some species of termite (e.g Nasutitermes exitiosus), sub-castes of large soldiers are dedicated exclusively to alarm propagation and serve no other function defensively (4.)
Like termites, ants also make use of pheromone chemicals. As ants are an eusocial group of insects, the use of pheromones as a means of chemical communication between other members of their colony is very important. There are several different types of pheromones, which are all species-specific, and each one can incite a different behaviour in the ants that sense it. (5.) These pheromones are produced in a number of exocrine glands, which include the Dufour, pygidial and mandibular glands.
Ants are able to pick up on these pheromones by use of their antennae, which act as olfactory organs and contain chemoreceptors. One of the most useful uses of pheromones by ants is recruitment pheromones, which are used to guide worker and soldier ants to food or prey such as termites. For example in the species Leptogenys distinguenda, it secretes a strong short-term pheromone from its venom gland to signal prey. Any foragers that detect the signal immediately head towards it, releasing more pheromones, and increasing the strength of the signal. Because of this, a small number of ants that encounter prey can rapidly attract enough colony members by releasing pheromones, attracting more ants, which amplify the signal until there are enough ants present to easily subdue the prey. (6.)
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Many ant species use soldiers as the front-line attack force in their predatory relationship with termites. These soldiers tend to primarily use the mechanical strength of their mandibles to subdue their prey. However, certain ants are able to produce chemicals to protect and to attack with. The Megalomyrmex symmetochus, from Panama in Central America, is an ant species which protects a species of fungus-farming ants in a symbiotic relationship. M. symmetochus produces an alkaloid venom used defensively that make the victims kill each other, an effective way of defending a colony. (7.). The Crematogaster striatula, from Western Africa, also uses an alkaloid venom, but not as a defence. These are a species of specialised termite hunter ants. The chemical is airborne and can be used from a distance, it takes around 10 minutes to affect the termite. These poisons also seem to rally other working ants, and repel other ants. (8.)
One of the primary benefits (evolutionarily speaking) of a eusocial mode of life, is how little the soldiers and workers mean in the grand scheme of colony life. As such, many eusocial insects (such as bees) have evolved suicidal tendencies with which to defend the colonies, and termites are no different. The way in which termites sacrifice themselves is called autothysis. This is a process by which an organism destroys itself via internal rupturing culminating in the organism exploding. Although self-destructive behaviour is found in many termites, the end result can vary from species to species. In the termite species Globitermes sulphureus the frontal gland sac has no opening on the outside of the termites body, and is filled with a sticky adhesive. The termite liberates this secretion by contracting its abdominal wall along an area of weakness, which ruptures the skin. (9.) The soldier termites normally do this after clamping an ant with its mandibles. And through this means the termites can block tunnels and trap ants in place hindering the ants advancement through the colony.
Image credits: expertoentermitas.org
Throughout this post various examples of the chemical warfare between ants and termites have been discussed. From the use of pheromones in both groups to communicate with their colony in organising the attack or defence, to the airborne weaponry employed by some ants, and the suicidal tendencies with which termites will defend their queen. It will be interesting to see what the future holds for these two rivaling insect groups, no doubt natural selection will continue to shape and mold these creatures into “endless forms, most beautiful and most wonderful” to quote Charles Darwin’s “On the Origin of Species”.
Written by Eoin Dillon, with contributions from Lauren Woodward, Sean Akira Ward and Samuel Awe
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- Title Image credits: expertoentermitas.org