Wednesday, May 30, 2012

Spicebush Caterpillar

While watering our flower gardens my wife came across the caterpillar of the spicebush butterfly.  Its bright yellow coloring made it stand out like a sore thumb against the rusty color of the mulch.

In its earlier stages these caterpillars take on the appearance of bird droppings a form of mimicry to help prevent it being eaten by predators.  In later stages, as with this one, its big faux eyes, gives it the look of a snake, which also acts as a predator deterrent.

Each time I touched it a tiny forked antennae would rise from behind its head.  This is known as the "osmeterium defense mechanism".  The osmeterium is a forked or y-shaped organ that emits toxic substances it manufactures from precursors obtained from the host plant it consumes.  A camphor tree, which is one of these host plants, is nearby.  Each time it feels threatened this wicked looking organ arises which not only acts as a "visual shock" to any predator but also emits its foul smelling concoction that supposedly offends them.

Below is a video I found on YouTube that shows this defensive behavior.

Normally these caterpillars are green, but turns this yellow (or sometimes orange) color prior to metamorphosis when it enters the chrysalis stage.  Below is a photo of a spicebush chrysalis I came across several years ago that was attached to our front door.

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