Friday, September 2, 2016

Spicebush Butterflies

While the numbers of Monarch Butterflies seen in Northeast Indiana has been very disappointing this summer of 2016, the numbers of other butterflies have filled the void of the missing Monarchs. Most prominent among these have been the swallowtail butterflies. Giant Swallowtail, Eastern Tiger Swallowtail, Black Swallowtail and Spicebush Swallowtail have been seen in large numbers to the delight of midwestern butterfly afficionados.
Spicebush Swallowtail, Popilio troilus troilus, early instars form a shelter by laying a web mat near the edge of the host leaf. As the web drys it contracts and folds the leaf forming a shelter for the growing caterpillar. The caterpillar hides in the shelter during the day and comes out to feed at night thus avoiding the possibility of being eaten by the common caterpillar predators. Host plants for the Spicebush Butterfly is Spicebush, Sassafras and Tuliptree among others.
As an early instar the main means of protection is looking like a bird dropping.  The brown 3rd instar caterpillar, with the white markings, makes a very convincing specimen. The green 5th instar caterpillar uses its false eye spots and humped body segments to look like a green snake and discourages predators. Notice that the black eye spots are complete with false reflective eye highlights.
The actual head of the caterpillar is usually tucked under the anterior of the body for protection.
To further promote the charade the caterpillar has a forked osmeterium that, when fully extended, resembles the forked tongue of a snake. The osmeterium also is coated with sticky, foul smelling slime that discourages those that would make the caterpillar lunch
.
 As the caterpillar gets closer to forming a chrysalis it begins to change color to a shade of light yellow. Finally it climbs a convenient stem, attaches a string seat belt and waits for the pupating process to begin
Chrysalises that form during periods of short day light (autumn) will be brown in color to blend better with the browning leaves of fall.  Chrysalises which form during periods of long daylight hours (summer) will be green to blend better with the green leaves of summer and emerge as adults that will lay eggs before cold weather sets in.  Chrysalises that form in late summer and early fall will enter a state of diapause, or suspended development, and emerge as an adult as the warm winds begin the following spring. 
Adult Spicebush Butterfly (male) 
Photography by Jeff Ormiston