On one of those steamy, hot, and humid mornings last month I found myself staring out of my air conditioned office at the Museum’s vibrantly blooming pollinator gardens. Movement caught my eye, and I wandered outside with my camera and tripod to catch some of the action. By the end of the day, I had realized that butterflies are not only lovely, but really, really weird.
A female monarch butterfly probes a bergamot flower for nectar using her proboscis. Video by Emily Stone.
As I’d hoped, a lovely orange butterfly was sipping eagerly from the pale purple bergamot flowers. Zooming in, I could watch as she probed the cluster of tubular flowers with her delicate proboscis. Except, calling it sipping isn’t quite accurate.
A butterfly’s proboscis is more like a paper towel than a drinking straw. Like a paper towel absorbs water when even a corner touches the puddle of spilled milk, tiny grooves on the inside of the proboscis pull liquids upward using capillary action. The inner structure of the proboscis also breaks the column of liquid into tiny droplets that pose less resistance.
Trying to suck the liquid up would require more force than the butterfly can exert, especially since butterflies don’t just drink thin nectar, they also consume water from puddles, juice from rotten fruits, animal tears, tree sap, and several other unexpected substances of widely varying thickness. As you might expect, different butterfly species have fine-tuned their proboscises to match their preferred food—even dried food.
Earlier this June, on a trip to Moquah Barrens, I snapped some photos of a dense mass of silvery checkerspot butterflies crowding around a lump in the sandy wheel track. What were they eating? A closer look revealed that the lump was a hairy, old wolf scat. Your first reaction to this might be a revolted “why?” Your next question might be “how?” Let’s tackle the “how” first.
Butterflies don’t use their proboscis like a straw, it’s more like a paper towel that carries liquid upward using capillary action. Photo by Emily Stone.
It’s actually pretty simple. Butterflies can send watery saliva down through their proboscis and onto the dry surface, where it picks up the substances they desire, and then travels back up the tube’s tiny grooves. Remember when we used to make Kool-Aid by adding water to powder?
The “why” is a little weirder. Butterflies are drawn to the scat (poop) of carnivores, but also to mud puddles, rotting plants, and dead animals. Those gross things are a source of the nitrogen and sodium that are lacking in the butterflies’ usual diet of flower nectar. In most species, only males will “puddle.” He then passes these valuable nutrients on to a female when they mate so that she can use them to produce healthy eggs. It’s called a “nuptial gift.” I mean, who wouldn’t want a little packet of the essence wolf scat or mud puddle on their wedding day? Seriously, those are two of my favorite things!
Speaking of butterfly mating practices (I did mention that the day was hot and steamy?), the Museum staff got a good laugh last week when one of our volunteers walked across town just so she could impress us with the fact that “butterflies have eyes on their genitals!” That sent me down a Google black hole!
Well, technically they are simply photoreceptors that can detect ultraviolet light, not eyes that can see movement and shapes, but it’s still an impressive discovery (by accident) into the sensory world of butterflies. This research was done on the Japanese yellow swallowtail butterfly in 2001, but extraocular photoreceptors—light-sensitive structures that are found outside of an eye—occur in many animals.
These silvery checkerspot butterflies are able to extract nutrients from wolf scat by sending saliva down their proboscis get it wet, and then drinking the resulting salt- and nitrogen-rich soup. Photo by Emily Stone.
What’s the use of literally having “hindsight”? It’s different for males and females. They both have two small patches of photoreceptors covered by transparent cuticle. In male butterflies, the patches are located so that when he has successfully connected with the female during mating, the photoreceptors go dark. Once he knows his aim is true, he can deposit both sperm and a nutritious nuptial gift that also acts as a plug.
In females, the photoreceptors aid in egg laying. The whole process takes at least three types of sensory organs! First, a female butterfly will use chemical receptors on her front legs to taste a plant and make sure it’s the right species for her caterpillars. Then she extends her ovipositor, and uses the two photoreceptors to tell her that it isn’t obstructed by a bit of schmutz, which would block light, and also eggs. Finally, as she pushes her ovipositor against the leaf, pressure sensors tell her that a leaf is really there, and she deposits an egg.
The full story of the discovery of the photoreceptors is pretty fascinating, and I recommend reading the full article, “Hindsight of Butterflies: The Papilio butterfly has light sensitivity in the genitalia, which appears to be crucial for reproductive behavior,” by Kentaro Arikawa of Japan.
That monarch who was (not sipping) on the bergamot flower fluttered away. I’ve always admired butterflies for their beauty and pollination services—but in hindsight—the weirdly elegant solutions they’ve found to life’s various problems are even more amazing.
Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at www.cablemuseum.org/books. Or order it from our friends at redberybooks.com to receive free shipping!
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