Make Your Garden a Haven for Insect Diversity
With pollinators and the other insects that help sustain our ecosystems in decline, now is the time to welcome what biologist E.O. Wilson called “the little things that run the world” into our gardens.
Many gardeners plant flowers to attract bees and butterflies, but insects can’t live on flowers alone. They require shelter, water, and in some cases, very specific food sources to raise their young. Consider creating a habitat for pollinators as well as the amazing array of less beloved, but still important, insects out there. Whether you add a few new plants to your stoop, set up a butterfly drinking fountain, or create a backyard meadow buzzing with pollinators, informed planting and maintenance choices can make a real difference.
Why Act Now?
Gardeners and farmers have noticed declining pollinator populations for some time, and alarming new studies suggest that the problem is worse than originally thought.
Though comprehensive local research is woefully sparse, researchers found insect biomass declines of 75 percent in protected areas of Germany and 10- to 60-fold drops in arthropod biomass in Puerto Rico, along with declines in the birds, frogs, and lizards that eat them. And a 2019 review warned that over 40 percent of insect species are on the path to extinction.
These disappearing six-legged wonders do much of the work of pollinating plants, including a huge portion of human food crops, and are themselves an important food source for larger wildlife. In his important book Bringing Nature Home: How You Can Sustain Wildlife with Native Plants, Douglas Tallamy notes that a pair of chickadees requires a staggering 6,000 to 9,000 caterpillars to feed just one brood of chicks. Threatened insects are the foundations of our food webs, and they need our help.
Addressing this crisis will require systemic changes in our environmental and agricultural policies. But gardeners can also provide meaningful support for a diverse range of native insects including moths, beetles, flies, wasps, and true bugs, many of which are beneficial to the garden as well.
Offer an Insect Buffet
Cultivating native plants and letting bugs nibble them is perhaps the most effective thing you can do to support a healthy population of insects and other wildlife.
It’s well-known that monarch caterpillars feed exclusively on milkweed plants, but many other insect larvae also have diets limited to just a few plant species. Of the eastern US’s hundreds of species of native bees, about about one-quarter are specialists, which means they can only eat pollen from one plant family, or in some cases a single species. Unfortunately, most garden plants are non-native and inedible to native insects. Indeed, these plants’ tendency to repel insects helped make them popular. It has also allowed some to spread unchecked as invasive plants in natural areas.
Names like the wild indigo duskywing, snowberry clearwing moth, and the goldenrod gall fly reveal how dependent many insects are on specific native plants. Boxwoods, rhododendrons, and turf grass from Europe and Asia are largely useless to North American fauna. But even a single well-chosen native plant can support a tremendous number of species. Tallamy found that an oak tree can support 534 species of moths and butterflies, a blueberry bush an astounding 288.
Which natives should you plant? In the mid-Atlantic, native oaks, willows, blueberries, cranberries, dogwoods, cherries, plums, birches, poplars, and crabapple trees provide for the greatest diversity of moths, butterflies, and specialist bees among the woody plants. Native goldenrods, asters, and sunflowers top the list of perennials. Goldenrod alone is a magnet for beneficial solitary wasps and soldier beetles, 11 specialist bees, scores of butterfly and moth caterpillars, goldenrod flies, wasps, and midges.
To learn more about the myriad planting options, consult Tallamy’s caterpillar-friendly plant lists, tailored to your zip code. The Xerces Society also offers regional pollinator-friendly plant lists, organized by bloom time.
The jury is still out on native cultivars—native species altered by breeding and sold with a moniker after the species name, such as Echinacea purpurea ‘Pink Double Delight’. Cultivars with disease resistance can be beneficial, and changing certain traits doesn’t seem to reduce ecological benefits. But, say, altering leaves from green to purple makes them inedible to insects, and changing a flower’s form and color can reduce its appeal to pollinators. Straight native species, ideally grown from local seed, are generally the best bets for wildlife. More nurseries will sell these options as demand grows—talk with your nursery staff to voice your support.
Once you have narrowed down your plant palette, you will still need to select options best suited for the light, soil, space, and moisture conditions in your space. Beyond that, be sure to select plants you enjoy!
Use Insect-Friendly Garden Design
A thoughtful plan and design will also help attract native insects. Aim for structural diversity, which means a mix of plant forms, including groundcovers, perennials, shrubs, and trees. These provide a rich variety of niches, with plenty of opportunities for nesting, foraging, and cover. Massing plants in drifts or repeating the same plants throughout your garden helps insects conserve energy in their quest for food.
Use bloom calendars to plan a succession of flowers so that pollen and nectar is continuously available for pollinators. Include plants that bloom very early and very late in the season. Native pussy willow, Salix discolor, is among the earliest blooms, its flowers providing a vital food source for the earliest emerging mining bees, mason bees, and other pollinators. New England aster, (Symphyotrichum novae-angliae), one of the last to bloom in the garden, is visited by queen bumblebees gathering a last bit of sustenance before winter hibernation.
Non-natives with showy flowers can be included among natives to provide additional pollen and nectar. Aim for diversity of shapes, colors, and forms. Umbel-shaped flowers generally provide the most benefit to insects, offering wide, flat landing pads and maximizing pollen and nectar stores.
Keep in mind, though, that some hybridized plants, such as mophead hydrangeas, (Hydrangea macrophylla), are completely sterile, offering only showy bracts and no pollen or nectar at all. The fluffy double flowers of most rose cultivars, dahlias, and camellias usually lack stamens and sometimes even pistils. Pollinators might waste a lot of energy searching them for pollen and nectar.
Add Insect Drinking Fountains
All living things require water, even brittle little insects. Birdbaths and ponds are too deep for them, posing a drowning hazard. Butterflies obtain moisture and minerals from mud and shallow puddles. You can recreate this key part of their natural habitat by making a puddling dish, partially filled with pebbles and sand, to hold water. A terra-cotta saucer would work well.
Insects also drink raindrops and dew that gather on plant leaves. Plants with very fuzzy leaves, very waxy leaves, or cupped leaves are particularly good at capturing water. Lady’s mantle, elephant ears, hosta, sedum, nasturtium, rodgersia, and native cup plant are some good options.
In order to produce the next generation, insects need safe, sheltered places to lay eggs, raise their young, and overwinter. And they have evolved to use those found in nature—leaf litter, dead stems and logs, even the abandoned nests of wasps and rodents. When we tidy our gardens, we sweep most of these nooks and crannies away. Consider leaving a bit more “mess” in your garden—leaf litter, wood piles, dead tree logs, stumps, and tree snags.
To welcome native bees, most of which nest underground, use groundcover plants rather than mulch to cover bare ground, and let some leaf litter accumulate in your garden. Many butterflies, moths, and other insects overwinter as eggs or pupae in the leaf litter near their host plants. Preserving leaf litter is also an easy and efficient way to compost in place and recycle nutrients back to your garden. Avoid bark mulch, which blocks access for bees looking for places to raise their young. And avoid disturbing established bee nests, too—they can be intricate, and take lots of energy to construct.
Many native bee species must find hollow stems in which to raise their young and overwinter. Plant raspberry, blackberry, goldenrod, sumac, and even roses for their hollow canes. In fall, cut a few of the canes at the top to provide access to those insects that don’t excavate their own holes, and leave the dead stems up through early spring.
An insect hotel is another option for attracting leafcutter, mason, and blue orchard bees, as well as solitary wasps, lady beetles, and other insects. These are attractive, functional structures packed with the different materials insects need for shelter, which can be especially hard for them to find in urban and suburban environments. They can be purchased, but are great do-it-yourself projects using mostly found materials.
Manage Pests Sustainably
A healthy garden, like any ecosystem, is a matter of balance, and gardeners must learn to tolerate some insect activity. A diverse garden rich in native plants and insects regulates itself and is better able to stand up to herbivory. If parasitic wasps find several different host caterpillars on which to feed their larvae, they will take up residence in your garden and be ready to spring at the first tomato hornworm to hit your tomato plants. Leafhoppers, scales, thrips, and aphids are natural and necessary parts of the ecosystem. To keep them in check, lure useful predators like flower flies, lacewings, wasps, beetles, dragonflies, and assassin bugs by planting natives, which attract a greater diversity of insect life.
Avoid chemical pesticides in all cases. Their use is simply not justified. Common pesticides are indiscriminate—they affect any insect that makes contact, and can persist in soil, water, and plant tissue for years.
Monitor your plants, notice what insects you see, and only interfere if your plants are sustaining significant damage. A rule of thumb is that a plant, once established, can survive the loss of one-third of its leaves through pruning or herbivory. Control pests preventatively by keeping plants healthy and resilient through proper siting and care. Interplanting is an age-old method of helping plants stand up better to herbivory—recent research bears out that marigolds really do protect tomatoes from whiteflies! Concoct a homemade spray of garlic and cayenne pepper to protect plants that are under siege.
If you do find that your plants have become infested with a problematic insect, such as the pesky squash vine borer or the invasive Japanese beetle, mechanical removal is best—squish as necessary. To clean off a plant overrun with mealybugs, scale, or aphids, apply mildly soapy water with a kitchen sponge. Stressed out plants are more likely to become infested, so be sure to address the root of the problem, which is likely not enough light or watering.
Raise Wild Caterpillars
Mail-ordered beneficial insects may sound like an eco-friendly pest management option, but they can introduce diseases into local populations and affect insect gene pools. It can be beneficial and fun to raise wild caterpillars, though. Plant their larval host plants and inspect the plants to find and identify them in late spring and summer. Then create a terrarium and feed them fresh leaves of their host plant daily. Release and repeat! Parsley, fennel, and dill work well for feeding eastern black swallowtails.
Enjoy Nature’s Bounty
Plant them, and they will come! Once you introduce insect-friendly native plants and maintenance practices to your landscape, you will get to enjoy the satisfaction of doing your part for the planet, and also the beauty of a tremendous show! Enjoy witnessing these fascinating creatures in all their diversity at your doorstep, from mammoth moths like Cecropias to teeny leafhoppers and sweat bees, all of which have a role to play in a healthy garden community.
Certify Your Garden Habitat
What could be more satisfying than a plaque to celebrate your insect-friendly garden? The National Wildlife Federation and the Xerces Society for Invertebrate Conservation will certify your garden with a sign. Posting yours proudly will help educate friends and passersby.