#osmeteria

Pipevine swallowtail eggs and caterpillars in the yard.

Like other swallowtail caterpillars, these pipevine swallowtail caterpillars have an interesting defense mechanism - hornlike organs behind their heads that are only visible when they feel threatened, as in the third photo.

These organs, called osmeteria, are covered with a sort of chemical repellent.  In this case the whole caterpillar is repellent to many predators because its favorite food is Southwestern Pipevine, which is chock-full of toxins.

More pipevine swallowtail caterpillars, from babies to big caterpillars to a chrysalis. 

In the first photo, you can see the spot above the caterpillar’s head where the hornlike osmeteria emerge when it wants to scare a predator away.  And in the middle photos, a better view of the actual threat display.

Often, but not always, the caterpillars take on a much darker color as they mature.  You can see that a couple of the big, sturdy caterpillars are a dark plum color with just a few red highlights.

The caterpillar climbing a wall, toward the end of the set, had formed the chrysalis by the next morning.  It started off yellowish green, and soon faded to a beige color that blended in with the wall.  Sadly, a storm blew the chrysalis away before the butterfly had a chance to emerge.

Have I mentioned that our yard was full of these little guys last summer?  So, lots of chances to watch them do their thing.