One of the most common misconceptions people have about ants is that they “attack” and eat plants. Although ants are pesky creatures, they cannot be blamed for munching on plants since they can’t digest plant fiber. So if you see them on your plants, they are usually “farming” other insects such as aphids, scale, whiteflies or mealybugs.
The photo pictured is of brown and black aphids, which can also be purple, blue, yellow, orange and green. They are the most voracious, prolific “rabbits” of the bug world and literally appear overnight (they clone themselves, I kid you not).
Aphids feed on plants using a mouthpart that functions like both a needle and a straw. They stick it into a plant and then drink up delicious plant juice. However, they cannot process all of it, so out the other end comes a sticky substance called “honeydew” which is an ant delicacy. The ants act like farmers and keep their little herds of aphids safe, and scare off the wolves (ladybugs, mantids, etc.) so they can harvest the good stuff.
To get rid of small infestations of ants/aphids, use a gentle spray of water. This will kill many of the aphids and annoy the ants. You can also use an insecticidal soap or oil , but only when temperatures are below 90°. These oils and soaps kill the insects on contact. Since they leave no residue behind, you will need to reapply. The directions will tell you what to do.
In closing, I must tell you that although ants may upset you terribly, make you curse and eat your picnic, in the end they are extremely important creatures. Ants are like tiny garbage trucks that clean up dead and decomposing plants/animals. If they didn’t, there would be a “pile up” of icky stuff nobody would want to mess with…
To learn about my favorite scientist, E.O.Wilson, a man who has spent his entire life studying ants, check out this link. There’s also a fabulous PBS video all about him.