Larvae of bagworm moths protect themselves by building spiral-patterned cases out of environmental materials such as twigs, leaves, and silk.
"The bagworm constructs a case around itself soon after hatching from its egg. The bagworm finds twigs or leaves in the tree or shrub where it feeds, and weaves these together in a silken case. As the bagworm grows, it adds to this 'armor.' The animal carries the protective case along with it as it moves around, poking out its head to feed.
"When the bagworm is full-grown, it uses silk to anchor the case to a branch or leaf. Sealing the opening with silk, it spins a silk inner case, or cocoon. There the caterpillar pupates. The adult male develops wings and leaves his cocoon to mate. The adult female never leaves her cocoon and lays her eggs in it. When the eggs hatch, the larvae crawl out of the case and move away, each to make its own tiny new case.
"The remarkable thing about the design of the bagworm twig casing is that it is designed to resist failure by crushing. The bagworm does this by placing the twigs in an ingenious pattern that, in section, forms a spiral configuration. Differing species apply this principle in various effective ways." (Tsui 1999:128)
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