Swamp Metalmarks Arrive

I received a couple dozen swamp metalmark caterpillars via Federal Express this morning. The swamp metalmark is the most endangered butterfly species that you've never heard of. It's one of the most endangered butterflies in North America. It's been extinct in Illinois for a while now, so mine had to come from Wisconsin.

Since about 2001, I've been working on a project trying to bring the species back to Illinois. This butterfly was probably never common anywhere. It lives in a rare type of wetland called a fen. Fens are spring-fed wetlands with alkaline soil and water. For reasons that are poorly understood, this type of environment poses challenges to plant life. Many of the species that you find there are fen specialists, and don't grow in other environments. Caterpillars of swamp metalmarks feed on one such plant called swamp thistle. There are probably only about 250 acres of fen left in the entire state of Illinois.

I first translocated metalmarks to an Illinois fen in 2002. I collected adult females from a fen in Wisconsin. Female butterflies mate shortly after emerging from the chrysalis, so it was no surprise that all of the butterflies that I captured were gravid. They laid eggs on potted swamp thistle in my lab, and in early October of that year, I released the caterpillars onto swamp thistle plants at their new Illinois home. The effort showed limited success. A small colony has established itself on this site, but it doesn't seem to be thriving. I'm hypothesizing that the founder stock did not include enough individuals to produce a robust colony. Unfortunately, even the existing colonies in Wisconsin are too small to support the removal of more than a small number of females.

I believe that the solution to the problem involves breeding one complete generation of butterflies in the lab. With most of the other species that we have bred in my lab, it's possible to produce upwards of 1000 new individuals from a starting generation of about 20. The problem is that this butterfly has only one generation annually and it overwinters as a larva. It's really hard to hold larvae over the winter in the lab without killing them in the refrigerator.

This year, I will try a new trick. There is some evidence that swamp metalmarks can reactivate, at least temporarily, any time there is a warm spell during the winter. This may mean that they do not need to hibernate. I will attempt rearing the caterpillars all the way through in the lab, obtaining a generation of adults some time in midwinter. If I am lucky, these will mate and produce large numbers of offspring. Next summer, if all goes according to plan, I will release second-generation adults into the wild.