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The Q? Blog

Hey Moth, That's a Great Rack on Your Head

by Devin Reese -- Jul 24, 2014
Devin Reese, smiling

Devin is the lead digital science writer for the Q?rius website. She writes and gathers media for the Smithsonian Science How? webcast series,...

Male fox moth (Macrothylacia rubi) with a magnificent set of antennae. Photo by Biopix, via EOL, CC-BY-NC
Male fox moth (Macrothylacia rubi) with a magnificent set of antennae. Photo by Biopix, via EOL, CC-BY-NC

Browsing through moths in the Q?rius Collections at the National Museum of Natural History during National Moth Week,  I discovered some impressive antennae. The wide, sturdy projections from many of the moth's heads looked like the blades of a helicopter. Contrast that to butterfly antennae so thin and delicate that they look like straight pins. Why the difference?

Despite their impractical appearance, the antennae are all about survival and reproduction. Moths are usually active at night, so they can't rely on eyesight. Instead, they have a highly developed sense of smell (olfaction). While our human sense of smell can be attributed to millions of sensory cells inside our noses, a moth's olfaction happens in the antennae.

December eggar mothA moth antenna is a feathery structure, made up of fine hairs. The hairs are smell receptors that detect molecules arriving from miles away. One antenna may have tens of thousands of hairs in a branching, flat shape with lots of surface area for receiving scent molecules. 

What scent could be so important to a moth? The scent of a mate! Female moths perch and send out chemical signals (pheromones) that are a great match for the male's smell receptors. Moth life spans are short, so they have to find a mate in a hurry.

Take the Atlas moth (Attacus atlas), for example, that I saw in Q?rius. A male Atlas moth lives only two weeks, during which it relies on its big antennae to track down a female. Atlas moths belong to the family Saturniidae, renowned for their smell capabilities. Also in Saturniidae is the record-holder for long-distance pairing up: the Indian luna moth (Actias selene). Researchers have reported that a male Indian luna moth can locate a female 6.5 miles (11 km) away.

Male moths are so attracted to a female's scent that it even becomes the focus of their mating. Check out the cynthia moth (Samia cynthia) in the Q?rius Collections. At dusk, when a female pushes out her scent gland from her abdomen, the potent perfume begins wafting into the air. The lucky male that hones in first grabs her scent gland with his front legs and mates with her, sometimes for many hours.

So, even though they look like helicopter blades, moth antennae have a lot to do with mating and nothing to do with flying…or do they? Scientists have found that some moths cannot fly well if they are missing parts of their antennae. In addition to being awesome olfactory structures, the antennae may be effective flight stabilizers. Like gyroscopes on airplanes, the sensory hairs track the movements of the moth in flight.

What else will we discover about these awesome racks on a moth's head? Learn more about moths in the National Museum of Natural History's entomology blog.


Categories: Q?rius News
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