You've Got To See This!

"You've got to see this!" is the call I heard from Susie, this morning.  I was horrified to see a large swath of bare stems loaded with nasty black caterpillars.  My first thought was I've got to get rid of these things.  But, first I had Beau run a quick id.  He came up with the mourning cloak.

One of a number of Iowa butterfly species that overwinter as adults. They spend the winter frozen in "cryo-preservation"  in tree cavities, beneath loose tree bark or in unheated buildings. Virtually anywhere they can fit into, to protect them from winter winds and keep them out of the view of birds and squirrels, will do as a hibernaculum (an overwintering den).
The caterpillars seldom move far from being in contact with one of their siblings. If disturbed on a branch, the mass of caterpillars will shake and vibrate in unison, thus, presumably, startling or frightening a potential predator. The bristling spines covering the caterpillars are another good deterrent to predators.

If the group's voracious appetite should happen to exceed the leaf capacity of the small tree or shrub on which they're feasting, they will march off together in a follow-the-leader fashion and seek greener pastures. By mid-June the caterpillars can be full grown. Because of the variability of the onset of spring in Iowa, the dates when the first batch of catepillars will mature varies a lot.


When they've reached full size the caterpillars go "walkies"; that is, they leave the host plant where they've been feeding in search of a site to pupate. Like most caterpillars, they seek to distance themselves from the site where they were last feeding and pooping, as this evidence will be apparent to potential predators. "Don't pupate where you last pooped", seems to be the rule! They may travel some distance, 10-50 yards, to find a safe site, usually beneath some kind of overhang, such as larger branches in the wild or under the eaves of buildings in cities.

And this is what they'll look like  as adults.

I'm glad I didn't freak out and go for the insecticidal spray.