The strange and slightly disturbing symbiotic relationship between ants and aphids has been made even more unsettling by a new discovery. It has previously been shown that the ants – which ‘milk' the aphids for a sugary liquid – will chew off and chemically retard development of aphid wings to keep them nearby. Now it seems that they also dope them up so even if they try to run away they don't get far (The Daily Telegraph).

“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,” says Vincent Jansen of Royal Holloway university (Press release)

The researchers found that aphids walking on filter paper travelled much slower when the paper had previously been walked on by ants than they did on plain paper. And when placed on dead leaves – which they should try to leave in search of food – having ants around significantly slowed aphid departure. “We believe that ants could use the tranquillizing chemicals in their footprints to maintain a populous ‘farm' of aphids close to their colony, to provide honeydew on tap. Ants have even been known to occasionally eat some of the aphids themselves, so subduing them in this way is obviously a great way to keep renewable honeydew and prey easily available,” says Tom Oliver, of Imperial College London (press release).

The paper doesn't seem to be online yet but should eventually appear here.

Image: A digital camera was used to capture the walking speed of aphids / Imperial