Barbara Faurot

In a column about gardens, we need to talk about some important members of the animal kingdom — arthropods. The biologist and naturalist E.O. Wilson calls them “little things that run the world.” 

The class Insecta, one of the nine classes of arthropods, includes nearly a million described species. Of these, most are beneficial in a garden. Fewer than 1 percent are potential pests. 

Insects and other arthropods live in all habitats. They perform essential functions: They are recyclers, pollinators, and pest predators. They provide sustenance for carnivorous insects, amphibians, migrating birds, and songbirds. Just one clutch of young chickadees will consume 6,000 to 9,000 caterpillars!

A healthy garden has a diverse community of insects, spiders, mites, centipedes, moths, beetles, butterflies, and bees — each with a unique and usually beneficial role in keeping the garden functioning well.

Beneficial insects and other arthropods most likely to be found in Pacific Northwest gardens fall into three main groups: 

Predators eat aphids, thrips, mites, whiteflies, mealybugs, and many others. Examples of beneficial predators are praying mantids, predatory bugs (damsel bugs, big-eyed bugs, minute pirate bugs, and assassin bugs), predatory beetles (lady beetles, ground beetles, earwigs, and lacewings), predatory flies (hover flies, bee flies, predatory midges, and dance flies), predatory thrips, ants, stinging wasps, hunting wasps, predatory mites, spiders, and centipedes.

Parasitoids are natural enemies of pests and they devour their prey from the inside out. Examples include parasitic wasps (who are tiny and prey on pest larvae) and tachinid flies (who resemble large house flies and prey on caterpillars).

Pollinators deserve special mention. Many of the predators and parasitoids listed above also provide flower pollination services. Most are tiny, and can only reach the nectar and pollen of small flowers. 

The non-carnivorous pollinators — native bees, honey bees, and butterflies — are attracted to gardens with a variety of flowers and caterpillar host plants. The western tiger swallowtail (Papilio rutulus) is a good example of a pollinator who relies on diverse plants for all stages of its lifecycle. The caterpillars prefer maples, willows, and cottonwoods, while the adult butterflies feed on lilac, columbine, phlox, and other flowering plants. 

The key, of course, is to get the helpful predators, parasitoids, and pollinators to visit and stay. 

Some species such as lady beetles, lacewings, or predatory mites are available for purchase from commercial suppliers. However, research by WSU and others shows that the benefits of introducing these purchased insects are usually short-lived. They may disperse and leave, despite the presence of prey and nectar. The unintended consequences can include competition with local native insects or introduction of unwanted parasites. 

A better approach might be to add plants known to attract these beneficial insects. Fernleaf yarrow, coriander, dill, and fennel are just a few examples of plants with compound umbels preferred by lady beetles and lacewings. Spearmint and candy mint have been shown to attract beneficial predatory mites. 

The best overall strategy is to be a good garden host. Offer a diversity of local flora with a long span of blooming and fruiting times. Native species are a good choice, as research across the country shows that native plants can support many times the number of beneficial insects compared to non-native species.

Plan to provide overwintering habitat, leaving some native vegetation, old canes, coarse mulch, and “duff” undisturbed during fall and winter. A source of water is also a good idea, even if it’s just a saucer filled with pebbles or a rock that collects water in its crevices.

The biggest barrier to attracting and keeping beneficials is the use of synthetic, broad-spectrum pesticides. Some native bees and butterflies are extremely sensitive to pesticides, whether narrow- or broad-spectrum. 

Traditional turfgrass lawns are also an impediment. It’s better to maximize plantings of shrubs and pollinator-friendly plants. Consider a “bee lawn” with a diverse mix of grasses, herbs, and wildflowers. 

Even a small space or hedgerow devoted to native plantings makes a big difference in providing resources for these crucial beneficial insects. Adding some flowers here and there across a neighborhood, or maybe replacing just a little bit of lawn with pollinator plants, creates a “flyway” or corridor of beneficial habitat. 

According to entomologist and wildlife ecologist Dr. Doug Tallamy, if we are willing to cut our lawns in half and plant native species, we could create a “homegrown national park.” Imagine expanding native habitat to equal the land area of all our National Parks combined, helping grow the diversity and abundance of the insects that support life on earth — one yard at a time. 

You can find some interesting ideas and resources at the nonprofit Homegrown National Park website: https://homegrownnationalpark.org/.

The nonprofit Xerces Society offers useful pollinator conservation resources and native plant lists for the Pacific Northwest: https://xerces.org/pollinator-resource-center/pnw. 

If you have questions about beneficial insects, insect pests, or suspected insect damage, Master Gardeners at the online plant clinic host weekly live Zoom sessions Mondays from 12:30 to 2:30 p.m. To make an online appointment or submit a written question, visit http://jefferson.wsu.edu/plant-clinic.

(Barbara Faurot is a Jefferson County Master Gardener and Master Pruner, working with other volunteers who serve as community educators in gardening and environmental stewardship.)