Butterfly can't leaf it alone, so biologist lends a hand
In a protected area behind Farber Library, he works to restore a beautiful insect and a more-natural order.
But this summer the senior lecturer in Sustainable International Development at Brandeis’ Heller School for Social Policy and Management has spent much of his own time and has recruited the help of others to protect a tough, stringy weed from Europe.
It’s in the interest of a higher cause of course – the survival and restoration of the Baltimore checkerspot butterfly (Euphydryas phaeton).
“When plants come from Europe that don’t belong here, that can be a very bad thing,” says Olson, “but not in the case of the checkerspot. By a quirk of plant chemistry, this weed is acceptable to the female checkerspot” as a host for eggs and source of food for newly hatched caterpillars.
Butterflies are famously flighty, but even by that standard the Baltimore checkerspot is eccentric.
Most butterflies winter over in a chrysalis; the checkerspot winters over as a caterpillar. Most butterfly eggs are laid individually; checkerspot eggs are laid in groups of 200 or more. Most butterfly adults live for a few weeks, fly for miles and refuel at flowers; checkerspots live only about one week, seldom visit flowers and rarely fly far from their place of birth.
Perhaps the most interesting oddity is that, with its natural food plant in steep decline, it has adapted to a completely unrelated and dissimilar species.
White turtlehead (Chelone glabra), which is native to eastern North America from Newfoundland south to Georgia, once was the only plant on which female checkerspots would lay eggs and the only plant on which young larvae would feed.
Modern times have reduced the presence of white turtlehead drastically. Partly that is due to the taming of rivers and streams that used to run wild occasionally, clearing off banks and creating new, sunny mud bars where turtlehead thrived. Elimination of natural predators like wolves and foxes also contributed, for in their absence rabbits and deer – which love to gobble turtlehead -- have proliferated.
Turtlehead became rare. But the checkerspot found an alternative in the narrow-leafed plantain (Plantago lanceolata). This summer Olson, who normally would want to be rid of invaders such as this, made special arrangements to protect and enclose specimens of it on the Brandeis grounds.
Creating conditions for checkerspot proliferation, restoring the food web by propagating white turtlehead and enjoying the bragging rights that come with success have made Olson a frequent visitor to the brush, weeds and wetlands behind Farber Library. His checkerspot project – three years old and growing – also has drawn in other Brandeis employees, from library staff to groundskeepers.
With the blessing and support of grounds supervisor Dennis Finn, this spring Olson roped off a grassy area behind the library that formerly would have been mowed weekly like most Brandeis lawns. Mowing does not kill narrow-leaf plantain, as homeowners whose lawns are afflicted with the weed can attest, but it can devastate checkerspot caterpillars. Olson then made a wire enclosure around one large clump of plantain for added protection from wasps and other predators. Then, in early June, he inserted about a dozen second-year caterpillars obtained from a fellow friend of the butterfly and held his breath.
The caterpillars entered the chrysalis stage in mid-June, emerged as adult checkerspots about 20 days later, mated, laid eggs and soon died. The eggs hatched in the third week of July, and more odd aspects of the checkerspot were observed.
Upon hatching, the larvae remained in a tight cluster on the plantain foliage and spun a gossamer tent around themselves. They fed on leaves enclosed in the tent and periodically shifted its position to replenish their food supply. Most butterfly larvae are independent feeders; checkerspots are distinctly social.
Another oddity occurs in early fall: The caterpillars cease feeding well before the first frost and just hang out in the tent. As cold weather arrives, they abandon the tent and descend into leaf litter, or, in meadows, into the thatch of grasses. There they spin a new, winter tent tight to the ground where they pass the cold months as dormant caterpillars.
“It is odd to think of a caterpillar -- such a creature of summer warmth, green leaves, and plenty of sunshine -- surviving ice and snow and many months of darkness,” Olson says, noting that while this lifestyle is not common, it is found in some other butterflies and moths, including the familiar wooly bear, the caterpillar of the Isabella tiger moth.
And there is a final, truly rare change in the caterpillars when they revive in the spring: Their very picky feeding habits will have melted away. In addition to white turtlehead and narrow-leaf plantain, over-wintered caterpillars will feed on broad-leaved plantain, an additional species of turtlehead, shrub honeysuckles, ash trees and many other plants.
This change from insects that will starve before they eat the "wrong" kind of plant to a much more generalized feeder is very unusual in the world of butterfly biology, Olson says.
For the rest of this summer though, the young caterpillars will feed strictly on plantain, snug in their tent, and still with the added protection of Olson’s screened cage. From the few dozen larvae first brought to campus there are now hundreds, and if most survive the winter, Olson will do away with his cages next year. The goal is for these rare butterflies to become common again, at least locally, and to soar freely on the Brandeis campus every summer, seeking out sheltered clumps of white turtlehead – and unmowed patches of plantain – entirely on their own.
Categories: Research, Science and Technology
