Spring butterflies to look out for in your blooming garden

In spring it feels like we live in paradise. We are surrounded by glowing green meadows and hillsides. Wildflowers are blooming, weeds decorate the landscape everywhere, and our gardens are waking up with new blooms each week.

Spring rains have led to lush growth in our wildlands and gardens, and feeding on this abundant spring foliage are a variety of native butterfly caterpillars, some of which may be sadly mistaken for pests.

When we think of butterfly gardens, what comes to mind are the flower nectar plants that attract butterflies. But we shouldn’t overlook the vital importance of the larval host plants caterpillars feed on. Each species of butterfly caterpillar eats plants in specific families. They cannot feed on just any plant. Butterflies have evolved with specific plant families and have developed the capability to process and tolerate the various chemicals - some toxic - that these plants contain. A spring flying butterfly like the Mourning Cloak feeds primarily on willows, which are not toxic but have bristly hairs on their backs to deter predators from eating them.

A spring butterfly that feeds on toxic plants is the Pipevine swallowtail butterfly (Battus philenor). Pipevine caterpillars are colored a striking black and red to warn predators they are toxic. These caterpillars are so toxic, birds actually vomit when they eat them. When caterpillars consume toxic plants, they become toxic for life, even when they transform into butterflies, from the chemicals contained in the toxic plants. Many are colored with red or orange colors to deter predators like birds from eating them. The Monarch butterfly is another example.

Mourning Cloaks (Nymphalis antiopa) are the earliest butterflies to be active in the year. Here in the North Bay they are active only until early summer to midsummer, when they enter a hibernation phase. They become active again in the fall for a short time before they find a safe place to overwinter in tree crevices or under the overhang of buildings. They are a mid-sized to large butterfly with charcoal black wings with a distinctive pale gold band on the bottom of each wing. Above this band are iridescent blue dots. Wing margins are irregular. They are primarily seen in riparian areas, but also in city parks or urban areas where they can find their larval host trees like willows, birch or elm. The first Mourning Cloak butterflies you see in spring are adults that have overwintered from an April or May hatching the year before. They fly during the first warm winter days when temperatures reach above 60 degrees and bask in the sun with their wings outstretched. Adults that have overwintered look faded and worn compared to the first deep black and gold offspring of the early summer season.

Mourning Cloaks are the longest-lived butterfly, surviving about ten months. The adults nectar on blooming willows, but feed also on tree sap, or gain minerals from mud. The females lay eggs in clusters on willows, poplars, American elm and birch. Caterpillars feed together communally in large webbed aggregations. Because of feeding in numbers, these caterpillars may be mistaken for pest insects and sprayed with pesticides, so be aware. Caterpillars of butterflies and moths form an important food for bird young, and spraying pesticides will deprive young birds of much needed food. The caterpillars often pupate away from the tree they fed on and pupae can often be seen on nearby building walls. Hosting these spring caterpillars is a wonderful event and should be enjoyed. Willows have a proliferation of leaves - and feeding caterpillars won’t harm them.

Caterpillars are black with red dots along the backs and are covered with black spines that act to deter predators. According to Dr. Art Shapiro, professor of Evolution and Ecology at UC Davis, a noted butterfly researcher and expert, populations in the Sacramento area have collapsed recently. Adult butterflies in this area migrate to the mountains to breed in summer and then back in late September to hibernate.

The adult male Mourning Cloaks are territorial. Males chose large sites (as much as 300 square yards) to defend against other males, and to look for females that may fly by. Because their territory is large, they fly from perch to perch and then rest, conserving energy while they spy for potential rivals and mates.

The Pipevine swallowtail is one of the best-known butterflies in Sonoma County besides monarchs, thanks to the charming and indefatigable efforts of the late Louise Hallberg, of the Hallberg Butterfly Gardens. Hallberg created a sanctuary for butterflies on the family property near Graton where she had lived her entire life. Annually she welcome the public to visit her garden. And although she died last year at age 100, the garden remains preserved under the aegis of a nonprofit organization and will again be open to visitors on June 17.

Swallowtail butterflies are large and often showy with vibrant colors, and epitomize the grace and beauty of butterflies. They are named for the tail-like projections from the bottom of their wings. Pipevine swallowtail butterflies are black, and on first glance resemble day-flying bats. The black is overlaid with an iridescent blue, and is quite striking up close. Pipevine butterflies are active in spring and early summer. The adults can easily be seen nectaring on the flowers of Centranthus ruber, a common non-native, spring blooming perennial plant that grows in many gardens and is a favorite butterfly nectar plant. The caterpillars feed exclusively on California pipevine (Aristolochia californica), a native deciduous vine that grows in shaded woodlands and along rivers and creeks. The pipevine is an interesting garden subject. The leaves are heart-shaped, soft and rather nondescript. The very unusual pipevine flowers appear on the bare stems in February and early March. They are chartreuse with red lips and easy to miss until you focus on them, when they stand out as one of the most interesting and unusual garden flowers. Slow to establish, but easy to grow, the vines are best on a fence they can twine through and where the flowers and butterfly larvae can be easily seen.

A woman I met recently described how she and her elderly mother, who lives in north Berkeley, learned about the pipevine and planted it on a fence in an effort to attract the butterflies. It took eight years for them to show up and for caterpillars to start to decimate the now vigorous vines covering a chainlink fence. Reports of a multitude of bats flying by day began to circulate in the neighborhood, until the neighbors realized it was really just a proliferation of the Pipevine butterflies. The caterpillars pupated on the sides of the neighborhood houses, and the original pipevine planting she and her elderly mother had begun became a neighborhood butterfly project that all delighted in.

Kate Frey’s column appears every other week in Sonoma Home. Contact Kate at: katebfrey@gmail.com, freygardens.com, Twitter @katebfrey. Instagram @americangardenschool.