Do Butterflies Taste With Their Feet? How Butterflies Sense

How tasting with the feet works

A butterfly’s legs are covered in tiny hairs and pegs called sensilla. Some of these are chemoreceptors, the insect version of taste buds. Each has a pore at the tip, and nerve cells inside respond to substances such as sugars, salts or particular plant compounds.

When a butterfly lands on a flower or a drop of sweet liquid, the receptors on its feet detect sugar. This triggers the proboscis, the coiled feeding tube, to unroll automatically. Classic experiments in the early 20th century by the American biologist Dwight Minnich showed this with red admiral butterflies: when their feet touched sugar water, they extended their tongues even though their mouthparts were not touching it.

The proboscis has its own taste receptors near the tip, so a butterfly can taste food twice: once with its feet and once as it starts to drink. For more on butterfly diets, see what do butterflies eat?

Drumming: how females choose a host plant

Taste on the feet matters most when a female is ready to lay eggs. Most caterpillars can eat only certain plants, so laying eggs on the wrong one would doom her offspring.

Before laying, the female lands on a leaf and rapidly taps or scratches it with her front legs. This behavior, called drumming, breaks the leaf surface and releases its chemicals. Special sensilla on her front legs, which are far more numerous in females than in males in many species, then “read” these chemicals. If the taste is right, she curls her abdomen and lays an egg. If not, she flies off.

A female monarch butterfly drums on leaves to find milkweed, the only food of monarch caterpillars, and tends to lay a single egg on each plant. The painted lady is much less fussy and lays on thistles, mallows and hundreds of other plants, but it still tests leaves with its feet.

Why many butterflies walk on four legs

Monarchs, painted ladies, admirals, fritillaries and their relatives belong to the family Nymphalidae, the brush-footed butterflies. In this family the front pair of legs is short and held against the body, and the butterfly walks on its other four legs.

These reduced front legs are covered in bristles, like tiny brushes, and are packed with taste receptors. In effect, they have become sensory tools rather than walking legs. In other butterfly families, such as swallowtails and whites, all six legs are used for walking, and taste receptors are found on the feet as well.

Smell: antennae as noses

Butterflies smell with their antennae. These long, clubbed feelers carry thousands of smell receptors that detect scent molecules in the air. A butterfly uses smell to find nectar-rich flowers, recognize host plants from a distance and locate mates.

Many male butterflies produce scents called pheromones from special scales on their wings, and females judge males partly by smell. Antennae also help butterflies balance and sense air movement during flight, and in monarchs they contain part of the timing system used during migration.

The clubbed tips of butterfly antennae are one of the easiest ways to tell butterflies from most moths, whose antennae are feathery or thread-like. See butterfly vs moth for more differences.

Vision: seeing ultraviolet

Butterflies have large compound eyes made of thousands of units, giving them a wide field of view. They are good at detecting movement and color, though their vision is less sharp than ours.

Butterflies see ultraviolet light, which people cannot see. Many flowers have ultraviolet patterns, sometimes called nectar guides, that point toward the nectar, and many butterflies have ultraviolet markings on their wings used in courtship. Some butterflies have more types of color receptors than humans: the Japanese yellow swallowtail has been shown to have six classes of photoreceptors. Others, like the painted lady, see ultraviolet, blue and green but lack red receptors.

Can butterflies hear?

Some butterflies can hear. Many members of the brush-footed family have a thin, drum-like membrane at the base of the forewing called Vogel’s organ, which responds to sound. In the tropics, the blue morpho and its relatives can detect low-frequency sounds, possibly to hear approaching birds.

Cracker butterflies of Central and South America make audible clicking sounds with their wings and can hear one another. A group of moth-like butterflies called hedylids even has ears that detect the ultrasonic calls of bats. Many common butterflies, however, appear to have little or no hearing.

Taste on the feet in other insects

Butterflies are not alone. Houseflies, honey bees and many other insects also have taste receptors on their feet. Like butterflies, flies extend their mouthparts when their feet touch sugar. For insects that spend their lives landing on things, tasting a surface on contact is a quick way to tell food from danger.