Caterpillar Close-Up

This caterpillar is so laid-back compared to the two younger ones we are raising.  I took this photo after returning him to his container.  He had pushed the lid off during the night and was trying to get back in since that’s where his food is.

“Junior” continues to grow every day.  He is plump and green now, with a handsome horizontal stripe just out of view in this photo.  The brown portion is actually the caterpillar’s face.  Isn’t his coloring striking now?

The eyespots are part of the swallowtail family’s defense.  When they grow too large to be convincing as bird droppings, the next instars look more like little snakes.  I love this tiger swallowtail because the little black line above the pupil of the “eye” looks like an eyebrow, and truly does make this appear to be a face.  These markings confuse would-be predators into thinking the large caterpillar is actually a small snake.

What snake-like disguise would be complete without a forked tongue? This structure pictured below is called osmeterium (pronounced: äz-mə-ˈtir-ē-əm), and the caterpillar extends it when feeling particularly threatened.  One of the younger caterpillars is very feisty. Every time we pick up his container to replace his food supply, he displays this defense unique to swallowtails. 
According to the literature, this structure is actually a gland that also emits foul-smelling pheromones, although I haven’t noticed an odor yet when he does this.

You can see the eyespots and the green coloring starting to show through the skin.  This caterpillar molted the next day.  I think the blue spots are lovely.  They remind me of the color of chicory—my favorite wildflower.

In the last post, I mentioned my curiosity for finding the facemasks uneaten.  I did do some reading on caterpillar molting hoping to find out why the facemask is left behind when the caterpillar eats the shed skin.  I was unable to find any direct references to it, but I think I can safely guess why.  I found a fascinating video of a swallowtail caterpillar molting.  After it crawls out of the old skin, the larva rubs its face vigorously to dislodge the old mask. The facemask rolls away.  I viewed several photos of both swallowtails and monarchs in which the facemasks were at the floor of the container. 

Whether or not the facemask lacks taste or nutritional value remains a mystery.  But I think the main reason it doesn’t get eaten is that by the time the caterpillar finishes his post-molt resting period, he simply has forgotten where the facemask went or doesn’t want to expend the energy necessary to retrieve it. 

Ah. There’s so much yet to learn. :)

Here’s the video if you are interested.  Keep in mind that this is a different species of swallowtail, but the process is the same.

We have now added another caterpillar container to our collection.  Megan was following a clouded sulfur in the yard on Saturday.  She watched as it paused on a clover and laid a single egg.  It hatched yesterday and is even more tiny than the first instar swallowtails.
 

I am glad you are enjoying this experience with me.  I look forward to sharing more photos soon.

If you have found this post and would like to read how I came to be raising this caterpillar, check out the previous posts here:

• Birth (Caterpillars aren't "born", obviously, but "Hatch" doesn't sound quite as profound.)
• Instar