Monday, June 16, 2014

Unexpected Tiger Moth Larvae

The blooms of my favorite milkweed are quickly fading from the prairie landscape.  Spider Milkweed, Asclepias viridis, is an early season bloomer that generally ends its flowering period before the first day of summer.  Not only does this plant produce an amazingly interesting flower, it also is a focus of activity for a variety of animal species.  It’s impossible to look closely at these flowers without some small creature looking back.

The pale green flowers are impossible to miss.  If Spider Milkweed is in the mix, it will certainly be noticed. 

Having a multitude of insect visitors means a quick pollination.  Seed pods soon replace flowers.  By mid summer, seeds will fly and the plant will begin to enter its dormancy.

Among its many insect visitors, Spider Milkweed supports the larvae of the state endangered Unexpected Tiger Moth, Cycnia inopinatus.  The orange bodied larvae are easy to see against the green of the plant.

The Unexpected Tiger Moth is double brooded in southern Ohio and is generally associated with Butterfly Weed, Asclepias tuberosa.  The body color of the larva tends to blend with the orange flowers of the Butterfly Weed and provide some protective camouflage.  That strategy doesn’t work on the Spider Milkweed.  Many insect species that feed on milkweed develop toxicity by consuming and processing the toxic compounds in the plant.  Orange coloration is a common trait shared by these insects and indicates to predators that the insect is best left alone.  That may help this colorful larva to avoid predation.

I assume that the adult moth lays its eggs on the flower buds of the Spider Milkweed.  Signs of feeding on the flowers is the first clue that Unexpected Tiger Moth larvae are on the plant.  As the larvae grow, they move on to feed on the leaves.

During the last few years, I have noticed that the first brood of the Unexpected Tiger Moth utilizes Spider Milkweed and the second brood uses Butterfly Weed. That means it is necessary to have an adequate population of both milkweed species in order to have a healthy population of moths.  Currently at Blue Jay Barrens, Butterfly Weed is much more common than Spider Milkweed and the two species grow in different areas.  I am now attempting to establish Spider Milkweed populations in closer proximity to the Butterfly Weed to see if this increases the numbers of Unexpected Tiger Moths. 

Part of that activity will take place in my garden where this clump of Butterfly Weed has a history of hosting second brood Unexpected Tiger Moths.  It takes two or three years for a Spider Milkweed plant to reach flowering stage, so it will be a while before I know if my plan is successful.  I’m hopeful that I will eventually see this effort benefit the moth.  Even if it doesn’t, it will be nice to have more Spider Milkweeds growing in the fields.


  1. Hi Steve... Never heard of Spider Milkweed until now, strange looking plant!! Hope you have success with this plan !!
    The caterpillars will thank you !! : }}


  2. Hi Grace. If I'm successful, I'll be sure to post a lot of pictures of those orange caterpillars.