The new documentary Metamorphosis shows how caterpillars shed their skin multiple times on the way to the chrysalis stage. But how do they know when to molt? A new study ties it to oxygen sensors in their skin.
Science Daily reported on research at Duke University that increases our understanding of caterpillar molting. A biologist found that while the caterpillar grows, one part does not — the respiratory system. As the rest of the caterpillar grows, demanding more oxygen, the tracheal tubes remain unchanged.
“Sensing it is low on oxygen apparently signals to the insect that it cannot continue to grow without proceeding to the next stage of its development, by molting,” the article said. While shedding the old skin, the caterpillar gets a newer, larger set of fixed-size tracheal tubes to last it till the next molt.
By controlled experiments, the researchers determined that the caterpillars molt when they reach 4.8 times the weight of the previous stage. Amazingly, the signaling system runs the length of the caterpillar, because they can molt even with their heads cut off: “Even without mouths to eat and brains to release the molt-triggering hormone, ecdysone, the insects still shed their exoskeleton and tracheal tubing.”
Beautiful close-up photography of the molting process is featured in Metamorphosis, now available in Blu-Ray from Illustra Media. Order it from Metamorphosisthefilm.com.