Thursday, June 3, 2010

Giant Swallowtail Larva

This could be a fresh bird dropping, but it’s not. This is the larva of a Giant Swallowtail Butterfly. Bird dropping mimicry is one trick used to avoid being eaten by hungry birds.

That blurry, winged thing in the middle of the picture is a female Giant Swallowtail looking like she’s trying to deposit an egg. I’ve never seen a live Giant Swallowtail that was not moving. This one was no exception. She bounced across a couple of leaves and then shot out through the woods. These butterflies are fast.

This prickly Ash is what attracted her. This is the primary host plant for Giant Swallowtails in this area. It’s normally found scattered through the woods as an understory shrub.

Instead of eggs, I found a young larva. Larva of many species avoid feeding in an irregular pattern such as this, because it is likely to attract predators. That’s apparently not an issue when you look like bird poop.

The easiest way to find Giant Swallowtail Larvae is to view the leaves from below and look for their silhouette. Of course, lots of other things also sit on the leaf, so not every shadow is a larva.

The larva I found was not in an easy to photograph location, so I had to do a little work to get him properly positioned. First I used my walking stick to lower the branch and then I hung dead branches along its length to get the larva in just the right position. The larva is on the leaf in the bottom center of the picture.

Giant Swallowtail larvae have a special irritant producing gland that they bring into play to repel predators. This larva is not yet old enough to produce the irritant, but I was able to make it show the rudiments of the developing gland.


  1. Incredible! I'm just learning about butterflies and caterpillars, etc., and find this fascinating! I've not been so lucky, but I'm always looking. Thanks for sharing this information. It will make me look twice from now on. Nature is incredible, is it not? Bird poop, imagine that. ~karen

  2. Karen - I'm happy to share. It's amazing how easily most caterpillars can hide from view. I find a lot of caterpillars by spreading a white sheet under a shrub or tree and watching where the poop falls. I have a couple of sheets that I use just for stuff like this and I'm careful to make sure they don't make it onto someones bed.

  3. I have been reading up on that very thing, and as soon as it stops raining and blowing, I'm going to give it a try!! Thanks for the encouragement. I told everybody about your "bird poop" post, and even forwarded it to some! So fascinating. Thanks! ~karen