The little sphinx moth caterpillar was on a mission: To find a safe, secure spot where she could transform herself and stay alive during the cold, wet winter months ahead. On a warm September day last year I watched as she inched her way across half the length of my back yard, occasionally meandering around roadblocks like plant stems and small rocks that must have seemed like insurmountable boulders to her (although at one point she nimbly climbed up and over a small log in her path). A couple of times she burrowed down into loose leaf cover, but then moved on, perhaps surmising that a better place would come along. After I walked away for a few moments I lost track of her. Since my yard is a leafy nirvana for butterflies and moths such as her species (Smerinthus jamaicensis or twin-spotted sphinx) that need to nestle themselves in soil under fallen leaves so they can pupate over the winter months, she probably found a suitable place that would hold her until a warm spring day allowed her to emerge and take to her wings.
We’re nearing the end of National Moth Week, a short stretch of time set aside to appreciate these gentle, humble, and nimble flyers who tirelessly supplement the daytime work of bees, butterflies, and other pollinators, as well as offer food for other animals. They get a fraction of the attention that butterflies do and are often vilified, despite their close relationship, beauty, and rich diversity. Within their hidden world are unusual, intriguing, and dramatic behaviors. Moth species outnumber butterflies by around ten to one; there are more than 11,000 species in the U.S., with another 160,000 globally.
Gardens are very important places for moths since development and agriculture severely limit their habitat. There might be dozens of moth species inhabiting an ordinary urban or suburban garden, and the way you manage yours can affect the conservation of their populations, which are, as you might expect, seriously in decline, like most insects. Here are some tips:
Protect them from light pollution. For nocturnal and crepuscular moths, as well as other insects and migratory birds who use celestial navigation, unnatural lighting can cause disorientation and confusion, leading to exhaustion and death. The best way to help restore their natural behavior is to turn off all exterior lights, using motion sensors when necessary. If you must have lights on, use only dim bulbs in warm tones, which are less likely to attract moths. Draw shades and draperies indoors as well, to prevent light trespass.
Ease up on “clean-ups”. Adult moths and their caterpillars, as well as some butterfly species including the mourning cloak, need fallen leaves, stems, twigs and other plant debris to help them hide from predators and to provide suitable places to pupate and spend the winter. Let fallen leaves stay on soil and delay cutting back spent plants until well into spring (the later the better), rather than doing it in autumn or winter (and always check branches that may hold a chrysalis). If you must neaten up a portion of your garden in the spring/summer, leave collected plant material elsewhere in your yard.
Forget about herbicides and other pesticides, which can kill moths and other insects. This will also benefit your garden by increasing the number of predatory insects that help control the pesky ones. There needs to be a supply of prey in order to feed the predators—it’s a natural cycle that needs to be supported.
Limit hardscaping (concrete, gravel, decking) and increase the amount of area given to plants other than lawn, since moths and other wildlife can’t use hardscape for habitat.
Grow a wide variety of plants (preferably native species local to your area) to appeal to a diversity of moth species—everything from grasses and flowering perennials to shrubs and trees. Gardening for moths is similar to gardening for butterflies and other pollinators, although moths generally tend to feed on a greater variety of foods than butterflies.
As adults, most moths need a sugar source and they may feed on plant nectar, rotting fruit, or tree sap. Moth-pollinated flowers tend to be fragrant and pale or white, such as western mock orange (Philadelphus lewisii), oceanspray (Holodiscus discolor), and snow brush (Ceanothus velutinus), which allow nocturnal moths to easily find nectar after dark, so think “moonlight garden”. Moths that pollinate by day typically feed at flowers that native butterflies do, since they usually have long tongues. Some moths, like the twin-spotted sphinx, have reduced mouthparts and digestive tracts so don’t eat at all in their adult stage; they exist briefly only to mate and lay eggs, which in turn may provide food for predators like birds.
Almost all moth species need a host plant on which to feed during their larval stage. Many moth caterpillars eat leaves like most butterflies do, but some species may eat seeds, woody stems, or roots. The most important native host plants for moths and butterflies in the Pacific Northwest — considering the abundance of species they host — include Oregon white oak (Quercus garryana), oceanspray (Holodiscus discolor), and species in the following genera: Acer (maple), Alnus (alder), Arctostaphylos (manzanitas and bearberries), Ceanothus (wild lilac), Populus (aspen and cottonwood), Ribes (currants and gooseberries), and Salix (willows).