Smelling with your forehead
What Are an Insect's Antennae For?
An insect's antennae are not feelers. They are mostly its nose, and some can pick up a single scent particle.
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Step 1 of 5
A smell is a particle in the air.
Smelling anything means catching loose particles that have drifted off it. The more air you can strain, the fainter a smell you can find.
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Step 2 of 5
The surface is covered in pits.
Magnify an antenna and it is pitted with thousands of tiny holes, each holding nerve endings tuned to one shape of particle. A match sends a signal straight to the brain.
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Step 3 of 5
Feathery ones strain more air.
Some male moths have antennae like combs. Splitting the surface into branches multiplies the area enormously without adding much weight, so more of the air gets sampled.
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Step 4 of 5
Two of them means direction.
One antenna tells an insect a smell exists. Two, spaced apart, tell it which side is stronger — and following stronger is how it walks up a scent trail to the source.
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Step 5 of 5
They do other jobs too.
Antennae feel what an insect walks into, sense how damp and warm the air is, and in mosquitoes even pick up the hum of another mosquito's wings.
A male silkmoth can find a female from kilometres away by scent alone, working from a handful of particles a second.
The short version
Antennae are mostly an insect's nose: pitted surfaces that catch scent particles, and two of them give the direction to follow.
Try it yourself
Follow a cooking smell through the house with your eyes shut. You are doing what an ant does, with a much worse nose.