Butterflies eat with their proboscis. This long, narrow mouthpart has coevolved with the flowers a butterfly relies on for nectar, so not surprisingly the length of the proboscis is usually correlated with the depth of the corolla tube of the flower species on which it feeds. Because it looks rather like a drinking straw, it was always assumed that it works like one, too. But in science, assumptions can be dangerous!
Not long ago, an engineer who was watching his young daughters chasing butterflies became curious. How could butterflies suck liquid through a straw that might be several times their body length? According to the physics of fluid transport, this would expend more energy than it delivered—not a recipe for success!
Once the question was raised, other scientists became interested and further studies ensued. As a result, we now know that a proboscis works more like a sponge—soaking up the nectar via capillary action, aided by a suction pump in the head of the butterfly.
So the next time you observe a monarch fueling up on your milkweed plant, remember—there’s more to it than meets the eye!
Author: Lisa Schneider
Photo credit: Pam Ford