For the last half century, I have seen the habitat values of southeast Iowa steadily diminish, part of a process well underway before my time. Among the first to vanish entirely are the plants already rare, and the animals which uniquely depend on them. For example, in 1895, MacBride listed the pawpaw as being uncommon in southern Johnson County, and by 1918 it is not even mentioned on Brumfiel’s forest maps. Pawpaw leaves are the only food for the caterpillars of the zebra swallowtail butterfly and in 2007 the book Butterflies of Iowa finds only one breeding colony of this exquisite species in the entire state.
So in 2008 I began my home program to reintroduce three of the rarest species – the spicebush swallowtail, the pipevine swallowtail, and the zebra swallowtail, by developing a plantation of pawpaw, spicebush, sassafras, pipevine, and Virginia snakeroot, which are their obligate hosts. This plantation today covers about four acres, and all three butterfly species have already somehow found it within a couple of years. So here is “Highlights from Lon’s Rare Butterfly Project, 2015 Season.” This PDF also contains an introduction to my newer projects just launched, regarding habitat upgrades for hummingbirds and other rare butterfly species.
The fact that the butterflies found your plantation is amazing Lon – especially when you had explained there were very few breeding colonies in the state. I am wondering where they came from, if they were migrating over Iowa to places where they remain more common, or what? Do you have any idea?
Hello Connie,
There are still established populations of these butterflies where habitat remains in northern Missouri and western Illinois, which I think produce a certain percentage of pioneers willing to venture to the north and west edges of their range, which is here. But hard winters, like last year’s, hammer these populations and the next summer they send out fewer pioneers.
My evidence at home suggests I might now have my own barely established population of pipevine swallowtails and I’m expecting them to become regulars in future years, to be evidenced by double broods. By contrast, spicebush and zebra swallowtails don’t seem to have established a local presence yet and I anticipate visitors are from many miles away, because there are only a few, late in summer.
Butterflies and moths are known to be very responsive to certain odors, especially mating hormones. In one experiment, 27% of marked males of the Chinese saturniid moth Arctias selene released 8 miles away, came to a caged female releasing her pheromone, and the other males might have gone elsewhere to wild females, or been eaten by bats. And odor is a 2-way street, the males releasing their own seductive odor which makes the female more receptive. I suspect that odor also guides these butterflies to the plants their caterpillars need for food, and all the species in my plantation do have a distinctive odor (to me) especially when the leaves are crushed.
So I have deliberately sprawled my plantation out over an irregular four acres plus some hedgerow plantings that extend even further away, with the intention of creating a broad odor plume that extends miles downwind. These butterflies prefer to fly on warm sunny dry breezy days, and on these days the winds are usually from the northwest, which is a convenient arrangement for attracting flyers coming from the southeast of us. The females would be the ones most surely attracted to plant odors because they need to lay their eggs on the right leaves. I do not know whether the males are also attracted to plant odors (because that is where the females will be) or they are just attracted to females wherever they may be.
We might not be far from being able to directly test my hypotheses. Telemetry chips are now tiny enough to attach to small birds without obstructing their flight, and in the future may get scaled down enough to fit a large butterfly. But in the meantime, when I walk through my plantation on a good flight day, I crush a few leaves of each species, hoping to spice up the odor plume.
Cheers