Why Are Moths Drawn to Flames?

Around the world, moths make kamikaze dives into light bulbs and open flames with such regularity that they have their own idiom. What is it about lights that make moths so crazy?

For a long time, scientists blamed the moon. Moths used the moon as a navigational beacon, it was argued, keeping it at a constant angle to their direction of travel in order to fly straight. Light sources used by humans, whether they’re campfires or porch lights, threw a monkey wrench into this system. The moon is far enough away that the angle between it and a traveling moth isn’t going to change much, even after the moth flies a great distance. With a closer light source, though, the angle changes considerably after only a short distance. A moth confusing a light bulb or candle flame for the moon, the hypothesis went, would notice this change and attempt to correct its path by turning toward the light. After just a few course corrections, the moth would set itself into a tightening death spiral towards the light and eventually crash into it, either going down in flames or thwacking its poor little head.

On Second Thought...

Over the years, various holes were poked in this hypothesis. For one—and this is a big one—moths might not even use the moon for navigation.

There isn’t much evidence for it, especially when it comes to the over 50 percent of moths that don't migrate and wouldn’t have much use a celestial navigation aid in their short distance travels.

There’s also the fact that moths don't always circle around lights in a closing spiral like the moon hypothesis assumes. Most of the time, they actually head straight for it. Henry Hsiao, a professor of Biomedical Engineering at the University of North Carolina, has tracked moth flights as the bugs headed toward a light source and found that, most of the time, they fly in a straight line toward the light until they get very close, then veer off and circle at a steady distance.

Hsiao’s observations led him to develop a new hypothesis. He’s unsure what causes the moth to make a beeline to a light, but thinks that the circling behavior at close ranges is caused by a visual distortion common to all sighted creatures called a “Mach band.” The band is the region surrounding a bright light that is perceived as being darker than any other part of the sky. Hsiao thinks that moths hang out in the band because they want the cover of darkness for safety, and wind up circling the light until their flight path takes them away from the it (or causes them to crash into it).

Love Hurts

Another explanation, proposed by U.S. Department of Agriculture entomologists in the 1970s, is that the infrared light spectrum emitted by candle flames contains some of the exact same wavelengths of light given off by female moths' luminescent pheromones. In other words, it’s just male moths that are attracted to flames because they wrongly assume that they’re going to get lucky. This doesn’t explain their attraction to UV light, which doesn’t emit the same light wavelengths as moth pheromones, but it does say something very profound about the lure of love.

nextArticle.image_alt|e
iStock
arrow
Animals
Honey Bees Can Understand the Concept of Zero
iStock
iStock

The concept of zero—less than one, nothing, nada—is deceptively complex. The first placeholder zero dates back to around 300 BCE, and the notion didn’t make its way to Western Europe until the 12th century. It takes children until preschool to wrap their brains around the concept. But scientists in Australia recently discovered a new animal capable of understanding zero: the honey bee. According to Vox, a new study finds that the insects can be taught the concept of nothing.

A few other animals can understand zero, according to current research. Dolphins, parrots, and monkeys can all understand the difference between something and nothing, but honey bees are the first insects proven to be able to do it.

The new study, published in the journal Science, finds that honey bees can rank quantities based on “greater than” and “less than,” and can understand that nothing is less than one.

Left: A photo of a bee choosing between images with black dots on them. Right: an illustration of a bee choosing the image with fewer dots
© Scarlett Howard & Aurore Avarguès-Weber

The researchers trained bees to identify images in the lab that showed the fewest number of elements (in this case, dots). If they chose the image with the fewest circles from a set, they received sweetened water, whereas if they chose another image, they received bitter quinine.

Once the insects got that concept down, the researchers introduced another challenge: The bees had to choose between a blank image and one with dots on it. More than 60 percent of the time, the insects were successfully able to extrapolate that if they needed to choose the fewest dots between an image with a few dots and an image with no dots at all, no dots was the correct answer. They could grasp the concept that nothing can still be a numerical quantity.

It’s not entirely surprising that bees are capable of such feats of intelligence. We already know that they can count, teach each other skills, communicate via the “waggle dance,” and think abstractly. This is just more evidence that bees are strikingly intelligent creatures, despite the fact that their insect brains look nothing like our own.

Considering how far apart bees and primates are on the evolutionary tree, and how different their brains are from ours—they have fewer than 1 million neurons, while we have about 86 billion—this finding raises a lot of new questions about the neural basis of understanding numbers, and will no doubt lead to further research on how the brain processes concepts like zero.

[h/t Vox]

nextArticle.image_alt|e
iStock
arrow
TBT
One Small Leap: The Enduring Appeal of Mexican Jumping Beans
iStock
iStock

In the fall of 1923, street vendors in Santa Barbara, California received an unexpected bit of attention regarding one of their more popular wares: The San Francisco Chronicle wrote about the sellers' “freakish little brown seeds” that “cavorted about to the edification and delight of children and grownups."

Those “freakish” seeds were (and still are) known as Mexican jumping beans. Part novelty item and part entomology lesson, they’ve been a staple of street vendors, carnival workers, and comic book ads for nearly a century, thanks to their somewhat inexplicable agility. Some early theories posited that the beans moved because of electrostatic charging, or because of tiny gas explosions inside—but in reality, it was a larva living in the bean. In Santa Barbara, the local Humane Society was concerned that the tiny caterpillar was somehow suffering in the heat; a police sergeant confiscated several of the seeds and took them home to investigate.

THE BEAN MYTH

In truth, the bean is not really a bean at all but a seed pod. In the spring, adult moths deposit their eggs into the flower of the yerba de flecha (Sebastiana pavoniana) shrub, which is native to the mountains of northwestern Mexico. The hatched larvae nestle into the plant's seed pods, which fall off the tree, taking the larvae inside with them.

Each larva is quite content to remain in its little biosphere until it enters its pupal stage and eventually bores a hole to continue life as a moth. (But only when it’s good and ready: If the pod develops a hole before then, the caterpillar will repair it using natural webbing it makes.) The pod is porous and the larvae can eat the interior for nourishment. Metabolic water creates moisture for the larva, but it never needs to pee. Essentially, it's the ultimate in downsized efficiency living.

A Mexican jumping bean store display
Mike Mozart, Flickr // CC BY 2.0

When it's in the pod, the larva isn’t exactly dormant: It twists and contorts itself to create encapsulated movement, almost like the snap of a rubber band. When it moves, so does the pod. No one is exactly sure why they do this, though some believe it's to keep the pod from settling on a hot surface (as high temperatures can be deadly to the insect).

The larva will keep up this activity for six to eight weeks. If a pod appears lifeless and rattles when shaken, it’s probably dead. If it lives, it will go dormant in winter before creating an escape hatch in the spring and flying off to begin life as a moth.

CHEAP THRILLS

It’s hard to know who exactly first decided to begin hawking the “beans” for amusement purposes, though some credit an enterprising man named Joaquin Hernandez with popularizing them in novelty shops in the 1940s. Later, in the 1960s, Joy Clement of Chaparral Novelties noticed the beans after her husband, a candy wholesaler, brought them home from a business trip. Though she was initially confounded by their appeal, Clement agreed to distribute the pods and watched them grow into a significant success: Between 1962 and 1994, Chaparral shipped 3 to 5 million of them each year, and saw the bean transition from sidewalk dealers to major chains like KB Toys.

“There's not much you can buy at a retail store that can give you this kind of satisfaction for under a buck," one bean dealer told the Los Angeles Times in 1994. "It's one of the last of the low-end entertainments available in the world.”

Interest in the beans seems to come in waves, though that can sometimes depend on the weather in Mexico. The jumping bean's unusual insect-crop hybrid stature means that farmers in Álamos, Sonora—where the pod is harvested and remains the area's major export—rely heavily on ideal conditions. Lowered rainfall can result in lower yields. Álamos typically handles more than 20,000 liters of the pods annually. In 2005, thanks to unfavorable weather, it was just a few hundred.

BEAN PANIC

There have been other issues with marketing hermetic caterpillars for novelty purposes. A UPS driver once grew nervous that he was transporting a rattlesnake thanks to a shipment of particularly active pods. Bomb squads have been called in on at least two occasions because the noise prompted airport workers to believe a ticking explosive device was in their midst. And then there was the Humane Society, which remained dubious the beans were an ethical plaything. (Since the caterpillars repair breaches to the pod, the reasoning is that it seems like they want to be in there, though no one can say whether the insects enjoy being handled or stuffed into pockets.)

You can still find the beans today, including via online retailers. They’re harmless and buying them as "toys" is probably not harmful to the caterpillar inside, though the standard disclaimer warning owners not to eat the beans remains. The police sergeant in Santa Barbara found that out the hard way: After taking his nightly prescription pill, he felt an odd sensation and went to the hospital. After physicians pumped his stomach, they noted that he had accidentally consumed a jumping bean. In his digestive tract, it was leaping to get out.

SECTIONS

arrow
LIVE SMARTER
More from mental floss studios