It's amazing to watch the female butterfly crawling around on the net, sensing out the leaves underneath, then depositing eggs on them. Even through the tiny holes of the net, they manage to lay an egg on a leaf.
A Combination of Senses
"Monarchs use a combination of visual and chemical cues to find milkweed," says monarch scientist Dr. Karen Oberhauser. "Once they land on a plant, they use sensory organs on their feet and heads to tell them if it is a milkweed, and probably the quality of the milkweed."
It's difficult for scientists to study monarch's senses because an insect's senses are so different from ours. Yet even our own senses are mysterious. When we smell and taste we are actually sensing chemicals in our environment. People and monarchs do this in a similar way.
Chemoreceptors ("KEE mo ree CEP terz")
People and monarchs sense chemicals in the environment with special structures called chemoreceptors. They come in different shapes and sizes, but they work in the same way. When a chemical fits a receptor, the way a key fits a lock, the brain identifies the chemical.
Antennae Have Chemoreceptors
Monarchs use their antennae to detect plant chemicals. The antennae are covered with chemoreceptors, especially at the tips.
Legs Have Chemoreceptors
All six of the female monarch's legs have chemoreceptors. Here you can see the midlegs. Look closely and you'll see the sharp spines monarchs can use to cut the plant and release the chemicals that tell the monarchs it's milkweed.
Eyes sense light, not chemicals. Monarchs have compound eyes with thousands of lenses. They see thousands of single images at the same time. Monarchs can see in all directions at the same time, too. Monarchs do not see the world in a single image the way we do. The monarch's vision is specialized for seeing colors, direction and movement.