So a few days ago I spotted a couple of ants underneath some leafs of a major branch of a tree in my garden. Yesterday I had the impression the amount of leafs being occupied by ants has increased a lot what then made me curious. So I spent quite some time yesterday observing one of the minor branches the ants had been very active on by that time. What I figured so far:

Underneath each leaf the ants are gathering, is an insect that looks sort of similar to a fruit fly (gonna call it fruit fly for simplicity, despite it certainly is something different). Around that insect are varying amounts of dots, which could be eggs or larvae. The ants seem to collect something from the larvae and also seem to be interacting with the fruitfly.

One of the more active leafs, showing the ants gathering at a leaf of the minor branch

At some point I spotted on the far end of the minor branch 2 living fruitfly. They seemed to be not capable of flight despite having wings. So I concluded they must just have been hatched. They seemed to try escaping the branch, as they pretty directly were just running up all the branch. Having almost made it from the minor to the major branch, the 2 fruitfly came across an ant, which immediately attacked both of them on contact. I was expecting the ant to carry them away then. While being attacked, both fruit fly tried to hide in the attatchment point of a leaf. The ant was circling around the attatchment point of the first fruitfly I was wondering why it did not carry that fly away, since it could clearly geto to that fly. After roughly a minute the ant turned back to their hide, having fully ignored the second fly, after attacking it once, and also leaving the first fly motionless at the attatchment point it was trying to find cover in.

But what happened a few minutes later is what left me astonished. A few minutes after the 2 fruitfly had been attacked, roughly at the same time, they started moving again. But different then before (kinda looked as if they had been injured but not killed by the ant). They did not seem like trying to escape the branch anymore. But just slowly moving to the next leaf in range continuing for 1 to 2 centimeters going underneath the leaf and then stopping there. Pretty much being in a position, as a fruitfly is positioned underneath the other leafs, where the ants are gathering . After like 4 or 5 hours 1 ant for the first time scouted the leaf these 2 flys went on. And in fact, other than attacking them again, this ant interacted with the 2 fruitfly1 like the ants under the other leaves interact with the fruitfly positioned on those leaves.

picture of the ant making first contact with that specific fruitfly

By now (over 12 hours later) the 2 fruitfly are still there I just checked and the small fruitfly that was only being attacked once, disappeared. The other one still being at the very same spot it moved to yesterday, tho. I would consider them being dead. But I am not even sure about that.

So what exactly are the ants I observed there doing?

If any other pictures would be helpful ask for it, I can take them later today. Also I have a speculation what it could be that was going on here, but not sure if that would anyhow improve this OP. Oh, since I can't identify the species, it might be useful to know at least: this is happening in Bavaria - Germany

1 well with 1 of them, the other that had just been attacked once, was simply being ignored


1 Answer 1


From what you described, it seems to me the "fruitflies" are aphids and the ants are farming them. This is a widespread and common phenomenon known as ants-aphid mutualism.


I elaborate a bit. Aphids feed on plant sap, rich in sugar, which they don't digest completely. The excretions (poop) are thus still rich in sugar (you may have noticed how your car windows get sticky sometimes under tress - that's aphids poop, I believe). Some ant species co-evolved with particular aphids and collect their excretions, a valuable sugary energy source. In turn, ants protect aphids from predators and they move them around to cover other good plant spots for aphids to suck sap and even move them to different plant individuals. This mutualistic interaction between aphids and ants is quite common and causes a lot of economic losses to the agriculture sector.

The behavior you observed of an ant attacking aphids was probably more the ant checking them and trying to evoke a pooping response. Sometimes they get them between their jaws and carry them around. Aphids also have quite complex social structure, with an optimal spatial organization. Hard to say if ants are moving them around to reach this optimal "farm density" or for other reasons.

TL;DR ants farm aphids as humans farm cows. When ants interact with aphids they are mostly checking them and trying to get their sugary poop.


  • $\begingroup$ Yeah, I can Identify the "fruitflys" as one of the kinds being found in that wikipedia article you linked. But could you please elaborate a bit more on what is going on there? I.e. where were those individuals coming from that had been attacked in my observation and i.e. why had they been attacked? And why the attack seemingly caused a change in their behavior? $\endgroup$
    – Zaibis
    Oct 6, 2020 at 7:18

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