The Nose Knows

What am I looking at?

This is a portion of a single antenna from a geometer moth (the species of moth whose caterpillar stage is the inchworm). This type of feathery antenna is called a plumouse (from the Latin word pluma, meaning “feather”) or comblike antenna. It has a segmented stalk called a flagellum (1). The branches jutting out to either side are called rami (2). The rami are covered in sensory hairs called sensilla (3), which contain neurons that respond to specific stimuli. The branches increase the antenna’s surface area and hence the number of receptors it can carry. Click on the right arrow to see some additional views of a geometer moth antenna.

Biology in the background

Moths use their antennae for detecting airborne chemicals, just as we do with our noses, only with much higher sensitivity. For example, female moths can detect, at concentrations as low as one part per million, the chemicals emitted by the plants on which they lay their eggs, and the males can detect the pheromones secreted by female moths at concentrations as low as one part per billion to help them find a mate.

Besides olfactory receptors, the antennae of these moths contain two mechanosensory organs – called Johnston’s organ and Böhms bristles – which help them navigate while flying. Johnston’s organ detects angular changes in the position of the moth’s body while it’s maneuvering in the air, while Böhm's bristles register the position of the antennae themselves while the moth is in flight, providing information on the position of the antennae with respect to the body. These organs together act as a gyroscope for the moth as it’s flying.

The antenna of a geometer moth is about 1.5 millimeters wide, or roughly 20 times larger than the width of a human hair.

Technique

These images were created using confocal microscopy.