Butterflies use seat belts and Velcro to anchor cocoons.
A perfect chrysalis is needed when a caterpillar, or silkworm, prepares to change from pupae into winged adults. The insect cannot emerge until they are fully mature, so any structural flaws can be fatal. But just as important is a chrysalis’ ability to remain anchored in place–and according to a new study, when it comes to metamorphosis, a butterfly’s delicate silk threads are some of its strongest and most reliable tools.
Researchers at China’s Southwestern University recently studied the life cycles of two butterfly species–Danaus chrysippus (plain tiger) and Papilio polytes (common Mormon)– and two silkworm species. The team observed the caterpillars spin silk into pads that resembled nets when it was time to construct the chrysalises or cocoons of the silkworm and butterfly. The authors of a paper published in ACS Biomaterials Science & Engineering on July 22, explain that “the connection between the cremaster-shaped hook and the silk pad is similar to the Velcro-style hook and loop, except that it’s an anchor-shaped hook instead of a single one.” The team collected silk samples after the insects had begun metamorphosing to measure the diameter and tensile strengths. Researchers conducted a chemical test after noticing that silkworm’s silk was thicker and stronger. They found that butterfly silk did not have as many beta sheets, which are molecular structures within proteins. The caterpillars wrap 20 silk strands together to form a strap that is eight-times stronger than a single thread. The team’s abstract stated that “we discovered that butterfly pupae developed unique body features in order to form secure bonds with silk.” “This enables them to effectively undergo metamorphosis and endure harsh weather conditions and surroundings.”
[Related: How everyone can help monarch butterflies.]
The new study highlights the intense complexity and planning that needed to successfully undergo metamorphosis. Next time you pass a chrysalis or cocoon outside, take a minute to admire its incredible strength.
