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Photo by Marisol Ortega

Significant others: plants & insects

By High Line | September 14, 2021

The coevolution of living things over time has created beautiful and complex relationships in the natural world. A well-known example is the relationship between flowering plants and pollinating insects—their mutually beneficial relationship ensures plants are pollinated and, in turn, rewards pollinators with food sources of nectar and pollen.

Below, you’ll find some of the interesting relationships between High Line plants and insects you may find in the park and in this area. The mutual benefits, or commensal benefits (meaning one party benefits and the other isn’t hurt), include food sources for insects, pest protection for plants, shelter for overwintering insects, and of course, pollination.

While not all insect-plant relationships are beneficial to both parties—consider the caterpillar munching on a shrub’s leaves—most naturally occurring relationships maintain a delicate balance in the ecosystem. That caterpillar may one day grow into a butterfly that will help pollinate this plant or others in the area.

TREES

Bigleaf magnolia
Magnolia macrophylla
Pollinator/insect relationship: Tumbling flower beetle (Mordellidae family)
Location: Flyover, 24th to 27th streets
Additional insect relationships: Beetles

One of the oldest surviving flowering tree families, the magnolia is known not only for its big showy fragrant flowers but for its role in insect-plant coevolution. Magnolias are pollinated by beetles attracted to the flower’s strong perfume and in search of their protein-rich pollen. In general, the flowers of the magnolia haven’t changed much since those first flowers—male reproductive parts produce pollen first and the female organs mimic the males effectively tricking the beetle into spending time looking for pollen and pollinating the flower. The beetles that pollinate magnolias are not specialized to gather pollen, so these flowers are also designed to support the weight and clumsiness of the beetle.

Chokecherry
Prunus virginiana
Pollinator/insect relationship: Lunate Zale moth (Zale lunata)
Location: Woodland Edge, Little West 12th to 14th streets
Additional insect relationships: Bees, beetles, butterflies

Chokecherry is versatile and hardy. It can be found in many habitat types and plant communities from Canada to Texas. It flowers profusely in the spring, providing pollen and nectar for insects, and early summer berries feed songbirds and small mammals. Chokecherry is host to the Lunate Zale moth (Zale lunata)—pronounced “Zah’-lay”—a member of the Owlet group of moths that find Prunus leaves to be a delicious meal for caterpillar larvae. Zale moths are widespread in North America but may be hard to spot since their colors allow them to blend in with tree bark.

Bur oak
Quercus macrocarpa
Pollinator/insect relationship: Edwards’ Hairstreak caterpillar (Satyrium edwardsii)
Location: Chelsea Grasslands, 18th to 19th streets
Additional insect relationships: Bees, moths

As a family, oaks support more insects in all stages of life than just about any other tree—and the bur oak is no exception. Wind-pollinated, these dramatic trees don’t rely on just one insect for reproduction but rather host many, including the lovely Edwards’ Hairstreak (Satyrium edwardsii), a butterfly that will lay her eggs within the crevices and grooves of the tree’s bark. After hatching, the young caterpillars will feed on the tree’s buds during the day. As the larvae mature, the caterpillars switch to nocturnal feedings, choosing to hide during the day in ants’ nests found at the base of the host tree. The ants welcome the caterpillars—they benefit by dining on the honeydew the caterpillars produce and the caterpillars are equally grateful for the protection of the ants. Later, this adult butterfly pollinates other plants we have in the park like Indian hemp, goldenrod, milkweeds, New Jersey tea, staghorn sumac, and white sweetclover.

Sassafras
Sassafras albidum
Pollinator/insect relationship: RIGHT: Promethea silkmoth adult and larva (Callosamia promethea); LEFT: Spicebush swallowtail adult and larva (Papilio troilus)
Location: Chelsea Thicket, at 21st Street; Flyover, 24th to 27th streets; Coach Passage,
along 30th Street
Additional insect relationships: Bees

Sassafras is a spring bloomer (March–May), with its fragrant yellow flowers attracting many pollinators. Later in the season, these flowers produce fruits that also attract birds. The leaves of sassafras are an important larval host to several butterflies including the gorgeous Spicebush swallowtail (Papilio troilus) and even more dramatic-looking Promethea silkmoth (Callosamia promethea). Both species lay their eggs on the leaves of the sassafras; the swallowtail alone on the underside of the leaf, and the silkmoth in rows of 4–10 on the upper side. Adult swallowtails will also use these flowers and many others as a nectar source (they are generalists when it comes to their nectar sources) but the Promethea silkmoth does not eat as an adult—in fact, they have evolved to eat only in their larval caterpillar stage. The adults, like some other moths, do not even have mouths!

SHRUBS

New Jersey tea
Ceanothus americanus
Pollinator/insect relationship: LEFT: Bumblebee (Bombus genus) and RIGHT: poor miner bee (Pseudopanurgus pauper)
Location: Across the path from the Lawn, at 23rd Street
Additional insect relationships: Spring and summer azure butterfly, mottled duskywing butterfly

New Jersey tea is a low-slung shrub that usually remains about three feet tall and at least as wide if not more. This little bush has a storied history—the dried leaves were a favorite caffeine-free tea, popular during the Revolutionary War. The sweet smell of their spring and summer flowers may be what attracts the love of people but the nectar produced by the flowers is the allure of many long-tongued bees, butterflies, hummingbirds, predatory wasps, moths, and other insects. It has a pollen specialist—the poor miner bee (Pseudopanurgus pauper), an uncommon and very, very small bee. The male is five millimeters and the female just slightly bigger at five and a half millimeters. Ceanothus is also an important host to spring (Celastrina ladon) and summer azures (Celastrina neglecta) and the mottled duskywing (Erynnis martialis) butterfly caterpillars.

Sugar shack buttonbush
Cephalanthus occidentalis
Pollinator/insect relationship: TOP RIGHT: Hydrangea sphinx moth (Darapsa versicolor) and BOTTOM LEFT: Titan sphinx moth (Aellopos titan)
Location: Hudson River Overlook, at 14th Street
Additional insect relationships: Bees, royal walnut moth

The unique buttonbush shrub produces a one-inch globe of small white flowers on a single long stem from June – September. They have a fringe of pistils that extend beyond the sphere of blossoms, creating a “pincushion” look. Buttonbush is also a big help in freshwater wetland habitat restoration projects where it is used to stabilize soil and prevent erosion.

One of its common names, “sugar shack bush,” refers to its production of nectar and how attractive it is to many pollinators, including hummingbirds and just about every butterfly. It is also a host plant to North America’s largest and most impressive moths including the Titan sphinx (Aellopos titan), the Hydrangea sphinx (Darapsa versicolor), and the royal walnut moth (Citheronia regalis).

Summersweet
Clethra alnifolia
Pollinator/Insect Relationship: Bees, butterflies, Organ Pipe Mud-dauber Wasp
Location: Chelsea Thicket, at 21st Street
Additional insect relationships: Bees, butterflies

Summersweet is an important shoreline stabilizing and reinforcing plant, critical to streams and riverbanks, as well as seaside shorelines as sea levels rise. The insects that love and utilize summersweet are too numerous to name here—they support a wide range of generalists from Texas to Maine.

One interesting visitor to the late-blooming Clethra is the organ pipe mud dauber wasp (Trypoxylon politum). A nonaggressive iridescent black wasp that hunts spiders and sips nectar—what’s not to love? The organ pipe mud dauber gets its name from the pipe organ-shaped nests it builds.

Grow-low aromatic sumac
Rhus aromatica ‘Gro-low’
Pollinator/insect relationship: Bristle-legged moth (Schreckensteinia erythriella)
Location: Chelsea Thicket, at 21st Street; plantings next to the Pershing Square Beams,
at 30th Street and 11th Avenue
Additional insect relationships: Moths, butterflies

Often referred to as “fragrant sumac,” this low-growing cultivar doesn’t grow taller than three feet. Male and female flowers bloom in the spring (March–April), with female flowers producing fruits later in the season. When the glossy green trifoliate leaves are crushed they release a fragrance that is citrusy, spicy, and rich; they turn a vivid red-orange in the fall.

Rhus aromatica is also host to several moths and butterfly larvae including the diminutive bristle-legged moth (Schreckensteinia erythriella). About a centimeter in size, this micro moth’s legs look like tiny branches that they raise in the air while at rest. They feed on the flowers and fruit of the Rhus genus at night and are attracted to light so they can often fall victim to light pollution.

Swamp azalea
Rhododendron viscosum
Pollinator/insect relationship: Azalea miner bee (Andrena cornelli)
Location: Flyover, 24th to 27th streets
Additional insect relationships: Bees

Clusters of irresistibly fragrant, white (often with hints of pink or lavender), trumpet-shaped flowers appear in May, after its shiny leaves come in, and last through July. The flower’s corolla tubes provide a good indicator as to what may visit this flower and its value to specialized pollinators. Hummingbirds, long-tongued bees (miner bees, carpenter bees, leafcutter bees, and bumblebees bees all have long-tongued bees in their families), and butterflies with their long proboscis all coevolved along with flowers just like this one, allowing them to reach the nectar wells hidden deep within the throat of the flower. The azalea miner (Andrena cornelli) is the only oligolectic—or specialist pollinator—for azaleas and they have special scopa—or specialized pollen-carrying hairs—designed to carry azalea pollen, a critical part of their diet.

FLOWERING FORBS

Blue giant hyssop
Agastache foeniculum
Pollinator/insect relationship: LEFT: Great spangled fritillary butterfly (Speyeria cybele)
Location: Gansevoort Woodlands, Gansevoort to Little West 12th streets; Hudson River Overlook, 14th to 15th streets
Additional insect relationships: Bees, flower flies, butterflies, beetles

Opposite leaves that smell (and taste!) of anise when crushed, rigid square stems, prolific purple-blue blooms clustered on top of spikes in July through September make this hyssop one of the most ornamental of the native mints. Most mints are highly attractive to bees and this one is a stellar example. If you’re looking to support pollinators in your home garden, straight species are best—human-developed cultivars often provide inferior resources. Agastache foeniculum is your best bet and supports a wide range of pollinators from bees to butterflies, hummingbirds, and even beetles.

 


Download our Celebrating Insects guide to learn about the importance of insects, their interesting and critical relationships with plants on the High Line, what our gardeners do, and what you can do at home to support these vital creatures, and more.

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TD Bank is the Presenting Green Sponsor of the High Line.

Additional support for Horticulture on the High Line is provided by the Greenacre Foundation.

Celebrating Insects on the High Line is sponsored, in part, by Whole Foods Market.

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