Ants protect herds of hemipterans, but not for free!
Would you believe me if I told you that ants tend cattle for milk, just as cowherds do?
Well, that's almost true: the animals that ants tend are much smaller than cows, and belong to a group of insects called Hemiptera. They are found in small clusters (called colonies), usually on the young branches of plants.
Hemipterans have long needle-like mouthparts called stylets. They insert their stylets into the plant and happily suck the sap, as you would drink juice with a straw. This sap is rich in sugars and amino acids.
The Hemipterans retain the amino acids in their body, and excrete out the excess sugars and sap in little droplets called honeydew. This is what the ants love! They quickly sip up the honeydew, often directly from the Hemipteran’s posterior, store it in their mouths, and later take it back to their nest to share.
Just as cowherds look after their cattle, ants work hard to protect these juicy Hemipterans from predators such as beetles who love to eat them.
Once, while walking through a forest, I saw a colony of mealybugs that were being tended by some ants on a young branch. I felt a little naughty that day, and shook the branch a bit. You won’t guess what happened.
The ants ran helter-skelter, but not on their own. Each ant carried one mealybug in its mouth and ran to save them from the threat (me!). I felt guilty, but at the same time couldn’t help imagining what a human cowherd would do if a giant came after his cows. Surely, he couldn’t pick up his cows and run, right? But ants can lift many times their own body weight, so a measly mealybug is hardly a problem for them.
So ants and Hemiptera help each other, but what about the poor plants? You see, the sap that the Hemiptera feed on is actually the precious food that the plant prepares for itself, by photosynthesis in its leaves.
The food is then transported to various parts of the plants through channels called phloem. Because of the Hemipterans, the plants not only lose their phloem sap, but also become vulnerable to bacteria and viruses which enter the plant through the holes created by the stylets.
But some ants also help the plants on which they live by providing them security. When these ants come across trespassers such as caterpillars, which eat the leaves of their home plant, they bite and chase them away.
So perhaps it's not so bad to give up some food to the Hemipterans, because ants might come by to tend them, and also begin to protect the plant from caterpillars. In this way, everyone benefits (except the poor caterpillar) – I leave you with that to chew on!
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