Many studies have established the Symbiotic Relationship between ants and aphids, that is where two or more animals depend on each other to survive. Aphids are small, soft-bodied, pear shaped insects which are commonly found on nearly all indoor and outdoor plants, as well as vegetables, field crops, and fruit trees. They feed on these plant juices and excrete a substance called honeydew which is rich in nutrients ants require. Honeydew is the clear, sticky dropping that is produced by aphids when they can't use all the sugar that they get from plants. In return, the ants will protect these aphids from their predators such as beetle, flies and wasps.
The ants will use their forelegs to stimulate the aphids to excrete honeydew, and store the honeydew collected in their abdomens until is full, whereupon they will return to the nest and regurgitate to feed other members of the colony.
Ants taking care of the aphids.
Nevertheless, while it may seem like both are benefiting from one another, ants obtaining food from aphids while aphids getting protection from the ants. Professor Vincent Jansen of Royal Holloway's School of Biological Sciences, concludes: "Although both parties benefit from the interaction, this research shows is that all is not well in the world of aphids and ants. The aphids are manipulated to their disadvantage: for aphids the ants are a dangerous liaison."
Research have shown that ants have been known to bite the wings off the aphids in order to stop them from getting away and the chemicals produced in the glands of ants can also sabotage the growth of aphid wings. In addition, new study has also pointed out that the ants' chemical footprints can also slow down the aphids' movements, thus keeping them close to the ant colony. Ants have even been known to occasionally eat some of the aphids themselves. Therefore, ants may seem like both a friend and a foe to the aphids.
References:
http://www.eurekalert.org/pub_releases/2007-10/icl-ha100907.php
http://www.ivyhall.district96.k12.il.us/4th/kkhp/1insects/aphid.html
http://www.youtube.com/watch?v=CwzUSRPo7PM&feature=related
“Aphid-Ranching Ants,” by John Walker. 10 Jul 2003.
“Herding aphids – how 'farmer' ants keep control of their food.” A joint news release from Imperial College London, Royal Holloway University of London, and the University of Reading, 10 Oct 2007.