Baby Saddlebacks

Relative to other caterpillars, slug caterpillars seem more fantasy than reality.

~David Wagner

It is getting to be that time of year – caterpillar time! As summer draws to a creeping close, one of the things that lifts my spirits above the stifling heat waves is the increasing abundance of larval Lepidoptera. And one of our favorite groups, the slug caterpillars, is starting to show up in greater numbers in our woods and yard. Earlier this week, Melissa was out in the garden and harvested some of our collards, since it was obvious they were becoming riddled by insect chewing. When she pulled one leaf she saw two tiny Saddleback caterpillars, Acharia stimulea. The female moth tends to lay clusters of eggs and the young feed gregariously at first. They are extremely variable in their choice of host plants. We have found them on tomatoes, various tree leaves, iris leaves, and now, collards. This may be why so may people recognize this as one of our most common so-called, stinging caterpillars as you can find them almost anywhere. You may accidentally brush up against one while weeding your garden and you won’t soon forget that encounter as they pack a powerful punch resembling the pain associated with a wasp sting. You can read more about them in an earlier blog post here.

Saddlebacks on collards

Two tiny Saddleback Caterpillars feeding on a collard leaf (click photos to enlarge)

Saddleback on collards

They are already sporting the pattern that gives them their name – the distinctive brown saddle outlined in white in the middle of their back

Saddleback with ballpoint pen for scale

Ballpoint pen tip for scale

Though these guys are extremely small (the tiniest Saddlebacks either of us has ever seen), I think they have probably molted at least once already. Online descriptions say that the earliest instars lack the prominent tubercles on either end.

Saddleback day 2

After one day, the caterpillars’ colors had already darkened and taken on more of the pattern of later instars

One scientific study I found said it was extremely difficult to accurately determine how many times this species molts during its larval development since the head capsule is hidden beneath the body and they almost always eat their shed skin. It is certainly more than the usual five molts of many butterfly and moth species, and may be as many as eleven or more and may require several months before pupation. Once again, I’m afraid we have taken on more than we bargained for in raising some caterpillars (we still have a few Cecropia larvae that hatched on June 10!). But, Saddlebacks will eat a variety of leaves are are not nearly as voracious in their feeding habits as most other species. I’ll try to keep you posted as they mature.

Saddleback caterpllar side view 1

What they will look like in a month or two


Can’t Touch This!

Saddleback caterpllar top view

Saddleback caterpillar (click to enlarge photos)

Well, it isn’t really a good idea to touch this, even though I have a few times. This is one of my favorite caterpillars, the Saddleback. It is the larva of an inconspicuous brown moth, Acharia stimulea.  The larva is named for the saddle-like pattern (green around the middle “saddle blanket”, with a brown oval spot “saddle” edged with white) in the center of the back.

Saddleback caterpillar side view

Saddleback caterpillar on Iris leaf

This distinctive larva is one of the unusual group of moth larvae known as slug caterpillars, family Limacodidae. Instead of having paired prolegs on their abdominal segments like most caterpillars, the slug caterpillars have suckers on the first seven segments. Larvae also secrete a semi-fluid silk as they move to help increase body contact and adhesion with the leaf (this can be seen in the first image). So, instead of crawling, they glide. I love the quote by David Wagner in his classic reference, Caterpillars of Eastern North America – “relative to other caterpillars, slug caterpillars seem more fantasy than reality”. Indeed, they are a strange lot, and this one is one of the strangest, and most painful when touched.

Saddleback caterpillar

Saddleback caterpillar showing spines

Several members of this family have the ability to inflict painful “stings” by means of sharp spines, which, on some species, have associated toxins to enhance the pain to the recipient. These stinging spines, known as urticating spines, are most numerous on the fleshy tubercles, or “horns”, adorning both ends of the caterpillar body. I have often found a caterpillar quite by accident when weeding in the garden or moving a plant leaf and then receiving a series of stings and resulting small welts where I brushed up against the spines. It feels a lot like a wasp sting but, for me, dissipates more quickly, although the reddish welts may persist for many minutes. But susceptible people may experience intense pain and allergic reaction, so caution is advised when you encounter these unusual beauties.

Saddleback caterpllar posterior

Saddleback caterpillar posterior view

When disturbed, the larvae often arch their body upward, exposing the intruder to more of the spines. They also have a false face on the posterior end, created by a pattern of light-colored spots. Even the cocoon should be handled carefully as they incorporate some of the irritating spines into the silk covering. These are generalist feeders found on a wide variety of plants, although I often find them on iris leaf blades in the garden. But, in spite of their formidable protection, I always enjoy finding these interesting caterpillars. Now, if only it will stay this way another week until the Museum’s largest special event of the year, BugFest (I’ll be volunteering at the caterpillar tent). I have a feeling I’ll be wishing that a lot in the next few days as I find various caterpillars about ready to pupate…what a difference a week makes!