Aphids are the enemy of agricultural production. They attach themselves to the stems and back of the leaves, piercing the plant tissue with needle-like mouths, sucking up the crop's nutrients like a vampire. If there are 1,000 aphids on a crop, it is impossible for that crop to grow. In order to seize the agricultural harvest, people tried in every possible way to get rid of aphids.
However, ants prefer to fight against people, pay more attention to aphids, and desperately protect them. If the aphid is blown off the ground due to strong winds or other reasons, the ants will gently pick up the aphids with their mouths and send them to the stems or leaves of the plant, or carry the aphids to their own caves, hide for a while, and then send the aphids to the plants. Ants come and go in and out of aphid colonies, driving away natural predators that prey on aphids, making aphids more brazen to harm crops.
Why do ants work so hard to protect aphids? We know that aphids feed on plants, and their excrement, honeydew, is a sweet and delicious feed for ants. Honeydew is a viscous, transparent, sweetened substance containing sugar, protein, dextrin and other ingredients. In plots where sorghum aphids are severely affected, when thousands of aphids spray honeydew from the anus, it is like a drizzle. Ants love to eat this sweet substance, and wherever it smells honeydew, it rushes in droves.
Sometimes, we also see more interesting phenomena in the fields where aphids occur: when ants eat honeydew in the aphid colony, they will also use their stick-like tentacles to pat the abdomen of the aphid, so that the aphid secretes more honeydew to satisfy its appetite. Darwin wrote about this phenomenon as early as in On the Origin of Species: "... So the ants began to use their tentacles to pat the abdomen of the aphid, first this one, then that one, when the aphid once felt the antennae of the ant, immediately raised its abdomen, secreted a drop of clear sweet liquid, the ant hurriedly swallowed the sweet liquid. Even very young aphids have such actions, and this activity is instinctive, not the result of experience." Ants play a protective role against aphids, and aphids reward them with honeydew, a phenomenon that is biologically called "symbiotic phenomenon".