Okay, so this is like really, really cool. Victoria Gill, writing for BBC, lets us in on the coolness:
In Africa and in the tropics, armies of tiny creatures make the twisting stems of acacia plants their homes.
Aggressive, stinging ants feed on the sugary nectar the plant provides and live in nests protected by its thick bark.
This is the world of “ant guards”.
The acacias might appear overrun by them, but the plants have the ants wrapped around their little stems.
These same plants that provide shelter and produce nourishing nectar to feed the insects also make chemicals that send them into a defensive frenzy, forcing them into retreat.
It is actually a fairly intricate relationship, with the ants territorially protecting a food source, including the swarming of larger herbivores, and the tree being able to chemically prevent the ants from causing too much havoc. Dr. Nigel Raine, at University of London, explained:
“The flowers seem to produce chemicals that are repellent to the ants,” said Dr Raine. “They release these particularly during the time when they’re producing lots of pollen, so the ants are kept off the flowers.”
In recent studies, described in the journal Functional Ecology, Dr Raine and his colleagues found that the plants with the closest relationships with ants – those that provided homes for their miniature guard army – produced the chemicals that were most effective at keeping the ants at bay.
“And that was associated with the flower being open,” he says. “So the chemicals are probably in the pollen” ….
…. The repellent chemicals are specific to the ants. In fact, they attract and repel different groups of insects.
“[The chemicals] don’t repel bees, even though they are quite closely related to ants. And in some cases, the chemicals actually seem to attract the bees,” says Dr Raine.
The researchers think that some of the repellents that acacias produce are chemical “mimics” of signalling pheromones that the ants use to communicate.
“We put flowers into syringes and puffed the scent over the ant to see how they would respond, and they became quite agitated and aggressive” he explained.
“The ants use a pheromone to signal danger; if they’re being attacked by a bird they will release that chemical that will quickly tell the other ants to retreat.”
Dr Raine says this clever evolutionary system shows how the ants and their plants have evolved to protect, control and manipulate each other.
B.D.'s Last Refuge 