Giant Swallowtail Update #3
(click on photos to enlarge)
On May 9, the caterpillars measured over 40 mm in their fifth and final instar stage as caterpillars.
Final Instar
One day while cleaning their cage, I accidentally touched the back end of one and it reared up brandishing its osmeterium, a forked appendage normally concealed in the thorax. Phew, it gave off quite a stink which remained on my fingers for several hours despite numerous washings. This surprise appearance coupled with an unsavory chemical release is thought to deter predators. I certainly retreated!
Osmeterium
They continued to eat until the 14th when they became lethargic. The next step was inevitable when I noticed a large voiding of undigested food on the floor of the enclosure. This was followed by a great increase in activiity — wandering all over the cage, presumably looking for the right spot to attach before transforming into a chrysalis. Once that spot is claimed, the caterpillar spins a silk thread or girdle by which it attaches to the substrate. In nature this would probably be the underside of a twig or branch some distance from the host plant. It hangs in a “J” shape and begins to noticeably shrink while its inner juices do some major reorganization.
![Hanging in the \](http://nestbox.com/blog/wp-content/uploads/2008/05/gisw_j_1257.jpg "Hanging in the \")
“J” shape
After about 24 hours, the caterpillar begins to pulsate and contract — slowly at first and then more frequently until the exoskeleton begins to split along the back and eventually falls off with a series of wiggles and twists. The resulting chrysalis is very tender and vulnerable at this time. It may take several hours for it to harden off to look like this.
Notice how well camouflaged it would be if hanging on a branch. If all goes well, an adult butterfly will emerge in about two weeks.
Published by Arlene Ripley on May 16th, 2008 Tagged Arizona, Butterflies, Nature, Tucson
July 13th, 2008 at 2:31 pm
Do you know if Giant Swallow Tail caterpillars are cannibals? I placed two large caterpillars and two smaller caterpillars in a butterfly enclosure with plenty of food and branches; and after two days, I can only find the two large ones. There is no way that lizzards or other animals could have gotten to them.
July 13th, 2008 at 4:01 pm
Leonor,
I don’t know that Giant Swallowtails specifically are cannibalistic but there are a few other North American butterflies in which the young exhibit this trait. One is the Harvester, another the Florida White. I’ve witnessed this with some moth larvae I raised and would not count it out as a possibility. Giant Swallowtail caterpillar eggs are laid singly and the caterpillars are solitary in nature. It’s possible that in a closed environment like a rearing cage the proximity of other larvae could cause cannibalistic behavior.