For many centuries it was a common belief that only humans kept other species as "livestock", but it turned out that we might not be as unique in terms of farming as we thought we are. Ants also take care of their herds of aphids to harvest their sweet honeydew.
Ants protect their aphids from predators and some parasites (Photo: Anita Diós)
There's a complex, mostly mutualistic relationship between some species of ants - called dairying ants - and aphids. This special bond has both lovely and darker moments, which range from the ants tending and protecting the aphids to the point of mutilating their wings... This means that while the plant lice often benefit from this relationship, there are times when it has a negative effect on them.
The basis of the whole relationship is the sweet honeydew that the aphids produce, and that is the favorite snack of the ants. Aphids have quite a large appetite when it comes to sucking the sweet, sugar-rich fluids of the plants, and the large amount of food eaten leads to a considerable amount of concentrated waste, which still contains a lot of sugar. This sweet energy bomb coming out from the aphids is a real "ant-magnet", and after the ants discovered a source of honeydew, they will not let it disappear...
(Photo: Anita Diós)
Some ants start stroking the plant lice with their antennae, which leads to the aphids excrete and release more honeydew over time. In fact, there are some aphids that need this kind of stimulation in order to release the honeydew, which means they depend on ants when excreting the waste. Beside the "milking", the ants have other chores to do around their "aphid herds".
First of all, the six-legged farmers protect the plant lice from predators and even some parasites - ants can be quite aggressive when something attacks their aphids, while some of them even get rid of the ladybugs' eggs when they encounter them near their "herds".
Some of the dairying ants are known to protect the aphids not only from other animals, but also from the chilling winter temperatures. They collect the plant lice eggs and place them into the nests, where they provide just the perfect conditions even when it's cold outside. When the weather is nice in the spring, and the eggs hatch, the ants bring the young aphids to plants they can graze on.
It's quite usual that ants guide the adult aphids to the best plants too, much like human shepherds would do. When they notice that one plant run out of nutrients due to "overgrazing" or other factors, the ants herd the plant lice to new sources of food.
(Photo: Anita Diós)
This might seem as both the aphids and the ants mostly just benefit from the mutualistic relationship, but it's not completely true - there are some serious disadvantages for the aphids. The most shocking thing that can happen to them is having their developing wings chewed or teared off by the ants. Other ants use semiochemicals to stop the aphids' wings from growing. The reason of this behavior is that ants don't want their source of food to just fly away when the aphids find the environmental conditions too poor - so the plant lice have no other choice than to stay even when normally they would forage for more food or better conditions.