A Puzzling Observation
As monarchs migrate through Texas, they often form roosts in pecan trees. People say the butterflies land on the leaves and appear to be eating. However, an adult monarch does not have chewing mouthparts, so what could a monarch eat in a pecan tree?
"Monarchs are interested in drinking fluids containing sugar during their migration," says Dr. Bill Calvert. "There are lots of aphids and lots of pecans in Texas. Monarchs have been known to take-in sugar on honeydew deposited by aphids on pecan leaves. Honeydew-coated pecan leaves, yum!" Follow the food chain to see what happens.
From Sunlight to Leaves
Plants need energy from the sun to make food. Most plants have green leaves, where photosynthesis occurs. Photosynthesis is the chemical process that converts carbon dioxide into organic food compounds, especially sugars. After the sugars are made, phloem cells transport the sugars throughout the plant. Think about sap coming out of a tree. That dripping sap usually comes from the phloem.
From Leaves to Aphids
Aphids are tiny, pear-shaped, soft-bodied insects. They have piercing, sucking mouthparts that remove water and plant nutrients from leaf veins. When the mouthpart penetrates the phloem, the sugary liquid is forced out. As they feed, aphids excrete large amounts of excess sugars. This sticky substance, called honeydew, collects on leaves.
From Aphids to Monarchs
Monarch butterflies use their proboscis to sip the honeydew from the pecan leaves. From sunlight to secreted honeydew, energy reaches the monarch.
People often consider aphids to be pests and look for ways to manage or eliminate them. This food chain shows how aphids can be beneficial. Living things can be connected in surprising ways!