What are these ants doing? (pictures)

[inane5]

I am growing long beans and winter melon in the same bed.

Earlier this summer, ants were factory-farming black aphids (black fly?) all over the the bean plant (particularly on young leaves/stems, flower buds, and on the actual long beans). In response, I used an organic soap spray and completely wiped out the black-aphids, and the aphids have not come back. This was a couple of weeks ago.

However the ants still remain, and they are doing something weird. The ants are hanging out at the end "nubs" of the plant. (I don't know bean plant anatomy at all., so by "nubs" I mean the stems that shoot out only to produce flowers and beans.) Almost every nub will have at least 3 ants camping in one position, with their heads occupied with something related to the "cavities" in each nub. (Again I don't know bean anatomy at all, and don't even know if these cavities are natural to bean plants, or something the ants dug.) Anybody know what these ants are doing?

Could I have wiped out their food supply to the point that they would eat the plant or drink it's sap? Is this something ants will resort to? And is this bad for the plant? Those are basically my questions. Please look at the pictures for more info.

FYI: I'm just guessing, but it looks like the cavities could be part of the natural plant? It's small but I don't see any honey-dew insects in the cavities, nor do the cavities seem to be increasing in size or quantity over time. Either way though, I am extremely ignorant when it comes to beans and ants. All I know is that ants are industrious and probably up to something evil, and I would like some idea what it is.

Thanks!


Pictures:
http://i44.photobucket.com/albums/f24/w ... G_8898.jpg
http://i44.photobucket.com/albums/f24/w ... G_8892.jpg
http://i44.photobucket.com/albums/f24/w ... G_8895.jpg
http://i44.photobucket.com/albums/f24/w ... G_8900.jpg

[Kisal]

Although I haven't verified it through research, I believe the small pits the ants seem to be gathering around might be extra-floral nectaries. If I'm correct, the ants are probably feeding on nectar.

[inane5]

Thanks Kisal. I googled extrafloral nectaries and it fits. I suppose there's also no harm in letting the ants eat nectar right? I'll just keep watching out for aphids.

[john gault]

I have yet to see any problems caused by ants in my garden.

[Fig3825]

Same exact thing going on on quite a few different varieties of veggies in my garden, discussion HERE. They are also on my beans. And my squash and watermelon. They seem to be concentrated on those plants. I do see the slightly elevated concentrations around the buds, but I also have them tooling around on my leaves and stems - perhaps they are just en route to and from the buds. It's hard to say on the watermelon as the buds are spread out along the vines and the ants are always going to and fro.

The ones I tried to nuke on a weed outside of the garden were also concentrated near a bud on the weed...