Wings Allow Escape From Spider Webs

light brown, yellow, and dark brown scales can be seen in this macro image of a butterfly's wing.

Biological Strategy

Butterflies and moths

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Expel Solids

Living systems must often discharge solids–such as seeds, eggs, pollen, and mineral salts–for reproduction, protection, or other reasons. Solids can be easily moved when a living system applies force to them. But creating that force requires energy, so living systems must either have efficient strategies worth the energy investment or use an outside force (such as gravity). For example, a tropical mistletoe positions its pollen so that the weight of a bird landing nearby triggers the pollen’s release onto the bird’s forehead. The bird then fertilizes other mistletoes that it visits.

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Protect From Animals

Animals–organisms that range from microscopic to larger than a bus–embody a wide variety of harms to living systems, including other animals. They threaten through predation, herbivory, defense, and parasitism, and they compete for resources such as water, nutrients, and space. Any given living organism commonly faces threats from a variety of animals, requiring strategies that effectively defend from each. Trout and other bony fish, for example, escape predators by having scales made of very thin, flake-like pieces of bone covered with slippery mucus. They also have behavioral strategies such as camouflage, fast swimming, and twisting and turning to achieve release from a predator’s grip.

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Insects

Class Insecta (“an insect”): Flies, ants, beetles, cockroaches, fleas, dragonflies

Insects are the most abundant arthropods—they make up 90% of the animals in the phylum. They’re found everywhere on earth except the deep ocean, and scientists estimate there are millions of insects not yet described. Most live on land, but many live in freshwater or saltwater marshes for part of their life cycles. Insects have three distinct body sections: a head, which has specialized mouthparts, a thorax, which has jointed legs, and an abdomen. They have well-developed nervous and sensory systems, and are the only invertebrate that can fly, thanks to their lightweight exoskeletons and small size.

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The wings of butterflies and moths help them escape spider webs and other predators because they have scales that easily detach.

Image: Mike Simpson /

Some of the scales have detached and at one end is the narrow protuberance that fits into the socket.

Image: Mike Simpson /

Some of the scales have detached and at one end is the narrow protuberance that fits into the socket.

Image: Janice Carr / Centers for Disease Control and Prevention /

Scalar patterning of a butterflys wing magnified 96x. Note the shingle-like pattern of the wing, which promotes heightened aerodynamic lift during the insects flight.

“Because butterflies and moths are always at risk of flying into spiderwebs, their wings are covered with detachable scales. When these insects are caught in a web or held in the grasp of a predator, the scales pull away freely and thus enable the moth or butterfly to slip away.” (Forsyth 1992:12)

Thomas Eisner writes about testing how spider webs hold prey by dropping various insects onto the webs. “Most did not have a chance. It was the moths that seemed most consistently able to escape. They fluttered vigorously the moment we put them into an orb, but as a rule they were detained only momentarily. Some bounced off the web without sticking at all. Others, which did not change direction upon impact, slid momentarily over the web’s surface, only to flutter free when they reached the edge. They all left impact marks on the webs where scales became detached to the viscid strands. Moth scars we came to call such telltale sites, and soon learned that they were common.” (Eisner 2003:218-220) [In the photographs of p. 219 of this book, he shows wing scales of a moth and empty sockets left after the scales detached.]

Last Updated October 24, 2016

References

Book

Exploring the World of Insects: The Equinox Guide to Insect Behaviour

30/10/1992 | Adrian Forsyth

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Reference

Book

For Love of Insects

31/10/2005 | Thomas Eisner

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