Monday, May 24, 2010

Bird Drop Caterpillars.

Japanese research has identified a hormone that allows some caterpillars to change protective coloration from a bird dropping (like our Giant Swallowtail pictured below) to the color of the leaf they live on.  (see Reuters picture on right)
"A special hormone -- juvenile hormone -- keeps larvae of the butterfly Papilio xuthus, which is commonly found in Japan, in their black and white bird-excrement camouflage.  As they reach the last stage of caterpillar development, levels of this hormone drop, triggering a transformation into the green leaf phase.
Juvenile hormones are known to regulate many aspects of insect development including molt -- when an insect sheds its outer shell -- and metamorphosis -- as when a caterpillar becomes a butterfly, he said."
Our Spicebush Swallowtail has a similar conversion in its final instar (larva) and posibly could share this mechanism.  The common Giant Swallowtail Butterfly (Papilio cresphontes) which I mentioned in the May 19th blog is in the same genus, but doesn't change color in the final instar.  (Picture from Whatsthatbug.com)  The large bird poop-like caterpillar is famous for its prominent stink glands, called osmetria, which protrude when it is threatened.  This appearance has given it the name "Orange Dog".  There is a lot of information on its entire life cycle at mybutterflyguide.com.
There will be multiple stages of the Giant Swallowtail's life cycle available at the Butterfly House at Close Gardens.

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