I keep a row of potted herbs along my front walk: parsley, sage, rosemary, and thyme—and oregano and basil. I cut fresh leaves in the summer for cooking, but a greater joy is watching neighbors on their walks stop and admire them. Young children at eye level seem especially intrigued. During friendlier, socially in-your-face times, I would wander out and invite them to pick a leaf and smell it. Children are eager to connect and learn if we let them.
My parsley bolted early this year, and I am letting it go to seed so I can collect some for next season. The parsley plant has an abundance of leaves and flowers—enough that, one day, I spy a fat green caterpillar climbing a stalk. It never ceases to amaze me how a butterfly looking to lay her eggs can find just the right species of vascular plant when there are 3000 different ones to choose from in Pennsylvania. This caterpillar is a parsley worm, an unflattering name for a rather attractive larva. When plump and ready to pupate, it sports green bands separated by black stripes with bright yellow dots. More impressively, nourished by parsley, it will metamorphosize into a black swallowtail butterfly.
I live in a new suburban village, which is still under construction but five years ago was a farm with pastures, fields, and hedgerows. When a 200-year-old farm is reshaped by earthmovers and dynamite, the future is not hopeful for diverse species and natural processes. And yet, here I am, charmed to find a swallowtail larva living on my potted parsley. Within a day or two there are many larvae, and they keep coming—perhaps twenty in total. At times they line up on the stems like the dump trucks that have lined up to haul topsoil away.
A pot of parsley is not a landscape. It is not even what is called a landscape element. It is, however, a green dot in the network of nature that stretches across the landscape. We often think about the engineered, hard infrastructure that creates networks, but there is another type of network that is important to landscape function and even more important to sustaining landscapes.
Nature networks play an essential role in the ecological structure and function of a landscape. Across much of the human-dominated world, these networks are relegated to remnants of old nature or overlooked places. With good landscape planning, these elements are protected and sometimes even restored and reconnected. Where I live, in a well-watered temperate climate with rich valley soils, the best nature corridors remain as forested mountain ridges or riparian zones along rivers and creeks. These connecting elements of nature allow for the movement and dispersal of plant and animal species. For them, it is a connection as important as the highway and railroad are to us. (Come to think of it, perhaps these nature corridors are essential for humans, too.)
Landscapes are home to many species and organisms. We humans are proficient at altering landscape structure to optimize our use. But what about all the other organisms—the black swallowtails and the great black wasps? How do they use the structure of the landscape to carry on their business?
Natural landscapes develop structure, evolving at a deliberate pace which allows time for organisms to adapt. As humans change this structure, species either adapt quickly or disappear. For some nonhuman animals, especially those with wings, the green patches need not be continuous but merely sufficient in number and spacing that islands of refuge exist across the landscape. This is the butterfly way.
The larvae first appear as thin black threads, just a half an inch long at the base of the parsley plant. They eat as they climb. Yellow dots begin enlarging, then green bands grow across their bodies, expanding like colorful accordions. In two weeks they go from tiny, pale yellow, spherical eggs to fat caterpillars. When ready, these larvae climb down and tether to branches in the shrubbery. Well anchored, they split their colorful skins open and shimmy out, leaving jade green pupae protected by hardening chrysalises. September pupae must prepare to wait out the freezing winter. Look as I did, I could not find a single one in the hedge. Those that overwinter turn brown and camouflage well. In springtime, when they emerge, the adult black swallowtails will be important pollinators. Perhaps the children who visit my potted plant will be charmed by a swallowtail hovering around my herbs. If it is May, she will be searching for fresh parsley to attach her eggs, thereby continuing the cycle for the first generation of summer.
Swallowtails prefer parsley, or anything in the carrot family, such as the Queen Anne’s lace growing in the wildflower patch that workers planted over the brand new natural gas pipeline just outside my front gate. There is milkweed in that patch, too, the preferred food of monarch butterfly larvae. This has me wondering. It is late in the season and I find but one caterpillar remaining with its black, yellow, and white bands on a stalk of partially eaten leaves.
Monarchs have a different agenda altogether—they are migratory. In the Atlantic flyway, it takes three generations to make the way north from Mexico every summer, and then a fourth for monarchs to return to their Mesoamerican mountain home. If this September caterpillar is to make it to Michoacán before it freezes, the larva must pupate soon in a chrysalis resembling a jeweled purse. An adult monarch butterfly weighs about half a gram, a little less than a mini marshmallow, and yet that half a gram, milkweed-fed, has the power and innate navigation system to migrate 2000 miles to a mountain only known to ancestors.
Biology is wondrous at the individual organism level. Ecological landscapes aggregate and compound the wonder with connections that are sometimes easy and sometimes difficult to see. The milkweed I keep watch over each summer is directly connected to the fir forests of the Sierra Madre. I worry that, as patches of milkweed are paved over, there will be fewer caterpillars to grow into butterflies and fewer amazing feats of strength and navigation.
The parsley I plant every spring is a nursery for a year-round population of black swallowtail butterflies. I love watching them flit from flower to flower on a summer afternoon. Although my material life would probably go on just fine without them, the world would be a poorer place. The meadow garden and the herb garden serve as important reminders that the nature we make room for in our suburban landscapes has connections far beyond the front gate.