“Why are butterfly antennae smooth while moth antennae are feathery?”

The Eight-Year-Old inspects a monarch butterfly's antennae while at the Brookfield Zoo. (Photo: Shala Howell)

The Eight-Year-Old inspects a monarch butterfly’s antennae at the Brookfield Zoo. (Photo: Shala Howell)

No really, The Eight-Year-Old did use the word “antennae.” See?

butterfly question

The Eight-Year-Old didn’t trust me to remember this question, so she wrote it down. (Photo: Shala Howell)

And no, she did not get it from me. I’m much more likely to say “antennas.”  Since this note dates back to sometime much earlier this year, her second grade teacher probably deserves the credit. Or maybe Daddyo. He tends to be picky about things like that.

Finding the answer to this question was surprisingly difficult. There are all kinds of sources confirming the fact that butterflies have long, thin antennae that end in a ball or club, and that moths have feathery antennae that are wider in the middle and taper at both ends.

But very few of them talk about why. As far as I can tell, it gets down to how butterflies and moths use their antennae.

Illustration of the differences between butterflies & moths. (Image from Encyclopedia Britannica, 2010)

Illustration of the differences between butterflies & moths. (Image from Encyclopedia Britannica, 2010)

Feathery antennae give moths a better sense of smell

Butterflies and moths both use their antennae to smell food and find a mate. The antennae are dotted with lots of sense receptors that can pick up the scent of flowers or the pheromones given off by a potential mate.

The feathery construction of a moth’s antennae gives them a much better sense of smell than their butterfly cousins. All of those tiny hairs means more surface area to cover with smell receptors, and that makes moths much better at picking up odors. A moth’s sense of smell is so powerful, it can smell (and track down) a mate more than seven miles away.

Bonus random fact: Butterflies and moths also smell with their feet. When they land on plants, butterflies and moths can use their feet to tell whether the plant’s nectar is good to eat (is it sugary enough?) and whether the plant will be a good spot to lay their eggs.

Feathery antennae help moths navigate at night

Butterflies and moths both use their antennae to gather information about how the wind is moving while they are flying, which helps them navigate long distances and achieve some measure of stability in the air.

But because butterflies typically fly during the day, they can also use what they can see to keep themselves on track.  But moths fly mostly at night. Whatever information their eyes can pick up in the dark isn’t much help when it comes to making mid-air course corrections.

Instead, moths have specially developed sensors called mechanosensors at the base of their antennae. These mechanosensors are what actually keep the moths flying straight in the dark. Basically, as the moth flies through the air, their feathery antennae get pushed around by tiny air currents. Moths sense this mechanical movement through their mechanosensors, and can use that information to steer through the air.

The Bottom Line

Because butterflies fly during the day, they can use their sight to supplement their senses of smell and direction. Moths, which mostly fly at night, can’t. Without the bright colors of the flowers to guide them, they have to rely on their sense of smell to find food (and a mate). Those feathery antennae give the moths a much better sense of smell than their butterfly cousins.

Moths have a similar problem with flight. Unlike butterflies, they can’t simply use their eyes to see that they are getting off track, so they must rely on the wind currents tossing their feathery antennaes about to help them navigate.

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About Shala Howell

I spent two decades helping companies like Bell Labs, Juniper Networks, and a genetic testing company that was later acquired by CVS translate some of the world’s most complicated concepts into actionable, understandable English. Now I'm working on a much harder problem -- fostering children’s curiosity and engagement in the scientific, artistic, and linguistic world that surrounds them. The first book in my Caterpickles Parenting Series, What’s That, Mom?, focuses on how to use public art to nurture children’s curiosity in the world around them. My next book will focus on science, and how parents without a science degree can answer their curious child's questions without enrolling in a college level refresher course. In the meantime, you can find me blogging about life with a very curious Eleven-Year-Old at Caterpickles.com, chatting about books and the writing life at BostonWriters.blog, and tweeting about books, writing, science, & things that make me smile at @shalahowell.
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4 Responses to “Why are butterfly antennae smooth while moth antennae are feathery?”

  1. Pingback: Still twenty moth species flying in warm December weather | Dear Kitty. Some blog

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