After overwintering three giant swallowtail caterpillars that had pupated, Slate Mills resident Robin Williams was rewarded with seeing two emerge from their chrysalises as healthy adults this spring.
With a wingspan of 4 to 6¼ inches, the giant swallowtail (Papilio cresphontes) is the second-largest butterfly in North America and the largest native to Virginia. With stunning yellow-and-black markings on the top side of its wings and lighter markings underneath, in flight it seems to be flashing like an oversized daytime lightning bug.
Robin, a member of Old Rag Master Naturalists and the Piedmont Chapter of the Virginia Native Plant Society, had planted native hop trees (Ptelea trifoliata) on her property to provide hosts for these giants. This tree species and others in the citrus family (Rutaceae) host the giant’s caterpillars (larvae) and, while historically not numerous this far north, have been dwindling through destruction of native forest.
Last July Robin was pleased to see a giant swallowtail circling one of her hop trees, laying an egg on several leaves. These eggs represented the second of the two generations the giants produce annually this far north. The caterpillars overwinter as pupae and emerge in the spring as adults, if they survive the winter weather and predators.
To help them survive predation, Robin had put mesh bags around the branches the caterpillars were on, as I wrote about last year in my Sept. 24 column. She took this action on the advice of local butterfly aficionados Bruce and Susan Jones, and Mona Miller, who were “very helpful” throughout the entire process of the fostering the giants, Robin says.
When the larvae stopped eating early last September, Robin was sure that they were getting ready to pupate — form a pupa or chrysalis, a hard case that protects the caterpillar while it morphs into an adult butterfly. At that point, caterpillars typically leave the host plant, to avoid habituating predators to their presence there at a time when they are trapped inside chrysalises (albeit well camouflaged ones) with no foliage to hide them.
After again consulting with Bruce, Robin acquired a small mesh cage designed for rearing butterflies, transferring the caterpillars into it. When Mona pointed out that sometimes predators can get into these small cages, Robin’s husband, Bill, built a larger cage in which to put the smaller one.
As Robin learned from Bruce, overwintering butterfly pupae successfully indoors requires maintaining a balance of the right climatic conditions, she says. The temperature should be close to the temperature outside, so she put the butterfly cage on a shelf in her unheated garage, near a window but not in direct sunlight, which can desiccate the larvae inside the pupae, and she misted the pupae occasionally with water.
When milder weather arrived in early April, Robin moved the cage to her carport. By May, when she saw other swallowtails flying and the wafer ashes’ leaf buds starting to appear, she figured the giants would emerge soon, timing that to the availability of the host plant’s leaves to lay their eggs on.
On May 13, Robin discovered that two of the giants had emerged and were “flopping around” in their small cage. One obviously had gotten a head start on the other and was now very eager to get out, she says. With the wafer ash just starting to leaf out at that point, their timing was “perfect,” she adds. (No adult emerged from the third chrysalis, the larva inside apparently not surviving the winter.)
Before pupating, a butterfly caterpillar typically gets rid of all the frass (poop) in its intestinal tract, shrinking the larva’s size — to a little over an inch in the giant swallowtail’s case, Robin says. As a butterfly’s wings develop inside the pupa, they are tightly folded. After emerging, the adult unfolds its wings by pumping fluid into them. Once the wings dry, the butterfly takes off to find a mate and reproduce. (For more information and photos on the giant’s life stages, check out the University of Florida’s Creature Feature website.)
When Robin “carefully scooped” each of her giants out of the cage, the eager one crawled up her arm and onto her back, then took off, she says. The other wandered around on the bricks of the low carport wall, still “pumping and drying” before taking off three hours later. Although departing separately, both butterflies headed north up her driveway, “like they knew where they were going,” Robin says. “I figured they were going to Bruce’s” (northeast from her place), she added, chuckling.
Or could it be that global warming is enabling them to extend their range north? Butterflies of Massachusetts says that that commonwealth has been seeing resident colonies of giants since 2010, the first time since some were reported in the 19th century and these “may be expected to increase in Massachusetts with climate warming.”
Although colonies of giant swallowtails have been documented in Virginia in recent years, no giants have been recorded during Rappahannock’s annual butterfly count, which Robin and other members of Old Rag Master Naturalists started in 2011. But with conservation-minded landowners such as the Joneses and Robin planting host plants on their property, that could change soon: the Joneses’ naturalized property, now the Jones Nature preserve, is one of the count sites. (For more about this year’s upcoming count, see Jeff Smith’s June 23 article.)
Wherever her butterflies are headed, Robin says she hopes they find more host plants and continue to colonize Virginia and further north. With male and female giants looking the same, Robin says she isn’t sure of the gender of the ones she fostered. Who knows, maybe they will return to the host tree on which they started their lives, as butterflies often do. And if one is a female and the other a male, perhaps there will be more little giants on her hop tree later this summer.
© 2016 Pam Owen
Stink bug predator update
Sperryville resident Barbara Adolfi recently found this “bold jumper” spider (Phidippus audax) on the door handle of her shed, hanging on to a brown marmorated stink bug it had caught. “When I went to open the shed door, the spider scooted around and never let go of that stink bug,” she said. The spider finally settled into eating the bug. Such sightings of native predators eating BMSBs, from spider and mantises to birds, are increasing, indicating that our native predators seem to be warming up to this nonnative, invasive bug. To learn more about this jumping spider, visit Spiders.us.