Ant and cow on oak tree 01
It is well known that ants keeps aphids as men keep cows. Ants transport and guard the aphid and take honey dew form the aphid's bottom. Aphids stings its mouth tube into plants' phloem where produced sugar sap is filled with pressure. Then the sap pushed into aphid's mouth, and excess sap is changed to honey dew and put out from the bottom. The ant suck it and bring it back to it's nest. Perfect ranch.So when you see ants are going up and down in line on the tree trunk, it means they are keeping the farm up on the twigs of that tree.
Tsukuba, Ibaraki, Japan, June 2007