Saturday, August 31, 2013

Gulf Fritillary Caterpillar

My grand-daughter and I spotted the bright red-orange caterpillar of the Gulf Fritillary butterfly.  It measured around 2 ½” in length and was grazing upon the leaf of a passion vine.  Its coloration popped against the green background making it stand out brilliantly.  Typically caterpillars only come out at night to feed in order to avoid predation. But this particular one knows that most birds will avoid it because of it being toxic if eaten.  It's "warning coloration" (aposematism) alerts birds and other predators that it is not palatable.  
I’ve read accounts that say the leaves of the passion vine contain chemicals (cyanogenic glycosides) that are the precursors of cyanide, which is absorbed into the caterpillars flesh making it toxic to eat, creating a defense mechanism. But then I’ve also read accounts that say this is not true- that the passion vine contains no such precursors.  Nonetheless, however it gets its toxicity, it is known to somehow be toxic if eaten.
Most folks would probably steer clear of this beautiful caterpillar thinking it would sting with the black spines it possesses. To ease everyone's mind these do not sting, in fact the black spines are soft to the touch.  If you were able to zoom in on these spikes or “tuberacles” you would see that each one has tiny hair-like projections on them.  These are tactile setae or sensory hairs which are very sensitive and can detect changes in movement of the surrounding air.  Like that caused by the whirring wings of a predatory wasp or the flapping wings of a bird.  This sensation of air movement alerts the caterpillar of the predator and then in turn drops to the ground in order to try and escape being eaten or becoming a "wasp nursery”.
Suggested Reading:

Stinging Caterpillars of the United States
Parasitized Gulf Fritillary Caterpillar
Parasitized Gulf Fritillary Chrysalis
Wild Neighbors: Following the Passion Vines
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