Today I visited my neighbour and she mentioned that there were ants running up and down one of her plants (the photinia fraseri ‘Red Robin’ plant).
So I took a good look and saw that the ants stopped at the buds of the plant. A small group of aphids (plant lice) were sitting there while the ants were running around them.
An ant can ‘milk’ these aphids by gently tapping them on their backs. Now and then, the aphids secrete a sugary fluid called honeydew out of their bodies, which the ant will then consume.
Aphids produce honeydew by sucking up plant sap. Plant sap contains way more carbohydrates (of which sugar consists) than aphids can use, so they secrete the excess carbohydrates out of their bodies and this forms the honeydew.
Ants however, love this sugary liquid. The sugars in it makes it a high energy food source. Some ant species go as far as carrying aphids to their nests to produce honeydew for them, others protect them on the spot from predators (like the lady bug) and moving them around to other parts of the plant or even to other plants to get more of that delicious juice. Yes, those ants sure know how to protect their food sources!
But the ants also need to thank a type of bacteria for the honeydew. These bacteria (Buchnera aphidicola) live inside the aphids and allows the aphids to exclusively live on plant sap. Aphids, like other animals, need amino acids in order to live and grow. Plant sap is not very rich in amino acids and here is where the bacteria Buchnera comes in: it provides these amino acids. Some aphid colonies also host other bacterial species, to deter parasites or to counter the effects of heat.
So as you can read, several species work together and in doing so benefit from each other’s labour. There is much more to tell about this particular cooperation, but I wanted to keep things simple.
Further (basic) information can be found on: http://en.wikipedia.org/wiki/Aphididae http://en.wikipedia.org/wiki/Aphid http://en.wikipedia.org/wiki/Ant http://en.wikipedia.org/wiki/Buchnera_aphidicola
And a movie to end with: http://www.youtube.com/watch?v=43id_NRajDo&feature=fvwrel