How Caterpillars move - the larvae of the Tulip-Tree Moth (Callosamia angulifera) is a strange looking creature, but it is a great subject study how they get around so easily.
Biologists studying caterpillars have reported a unique "two-body" system of locomotion that has not previously been reported in any animal. The gut of the crawling caterpillar moves forward independently and in advance of the surrounding body wall and legs, not with them. This novel system may contribute to the caterpillars' extraordinary freedom of movement and provide insight for the design of soft-bodied robots. Anyone who has ever observed caterpillars knows that they crawl from back to front in waves. But advanced imaging reveals a surprising picture of what goes on inside.
The researchers used synchronized X-ray and visible light microscopy and videos to study the relative timing of movements of the crawling caterpillars' gut body wall and prolegs (unjointed leg-like structures on the mid-body that grip).
They found that the gut -- essentially a tube suspended at the rear and head of the caterpillar and decoupled from the body wall -- moved nearly a full step in advance of the surrounding structures. In contrast, gut movement was "in step" with motion of the head and rear.
Furthermore, points within the gut moved at different rates, suggesting that the gut was effectively shortening and lengthening during each crawl cycle.
"Although internal tissue movement caused by locomotion has been identified in many organisms, the caterpillars seemed to be propelling themselves by means of a two-body system -- the body wall container and the gut it contained. This may contribute to the extraordinary freedom of movement seen in these soft-bodied crawlers,"studied Manduca sexta.
More research is needed to determine if this phenomenon gives caterpillars an evolutionary advantage, in the same way that synchronizing breathing and tissue movements benefits running vertebrates, or arm swinging by walking humans increases stability and reduces metabolic costs.
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The tulip-tree moth is found in woodlands and forests from Michigan, southern Ontario and Massachusetts to northern Florida and Mississippi. We can have two broods here in the South, and mature caterpillars start showing up in June. The Caterpillars feed primarily on the tulip tree (Liriodendron tulipifera).
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