Bugs in the Backyard
About 88% of plants require insect pollinators, like this regal moth, to reproduce. Photo: Sean O’Donnell
If you grew up in the 1960s or 70s, you may remember late summer evenings as a kid, grabbing fireflies out of the air by the dozen and making your holding jar glow like a lantern. If you tried that today, you would be disappointed at the meager numbers of fireflies you’d find. Where did all those lightning bugs, as we called them, go? Sadly, their decline is part of a more general phenomenon. In recent decades, insect populations have drastically decreased all over the world.
The disappearance of insects has more far-ranging consequences than just the loss of a childhood pastime. The biologist E.O. Wilson refers to bugs as “the little things that run the world.” Doug Tallamy, a professor of entomology and wildlife at the University of Delaware, explains that “life as we know it depends on insects.” Tallamy says that, for too long, we’ve viewed insects as pests and assumed they are so common and plentiful that reductions in their populations couldn’t possibly be a problem.
Ecosystems are a delicate balance of various species of plants and animals interacting with — and depending on — one another. Globally, the number of invertebrates (the category that includes insects) has declined 45% since 1974. This has had a negative impact on the plant and animal species that depend on them. About 88% of plants need insect pollinators to reproduce. And insects are a food source for numerous animal species whose numbers decline along with the insects that sustain them. The loss of three billion breeding birds in the U.S. today compared to 50 years ago may be linked in part to insect declines. This is why, as Tallamy notes, “Insects are the currency in our ecological bank account.” Caterpillars, in particular, transfer more energy from plants to other animals than any other group of insects and are therefore crucial for many animals’ survival.
Multiple factors are contributing to the rapid disappearance of insects, including habitat loss, pesticide use, and light pollution. One fundamental cause of their decline (and one we can control) is the overabundance of non-native plants. We rarely think about the importance of protecting bug life in our backyards, most likely because we don’t realize how crucial it is to do so. We also tend to believe that just planting plenty of greenery in our backyards creates a welcoming environment for all animal life.
But plants from one ecosystem cannot do an equally good job of supporting life in a different ecosystem. Why isn’t a Korean dogwood just as good as our native flowering dogwood? The answer lies in the arms race between plants and the animals that eat them. Plants have evolved all sorts of defenses — nasty tastes, poisons, gooey sap, spines, tough coverings — to keep from being eaten. In turn, animals have evolved ways of dealing with those defenses so that they are able to eat those plants. Non-native plants (which Tallamy calls “biological pollution”) have defenses that our native insects are unable to overcome, making them useless as a food source for those insects. Therefore, native plants are crucial to a thriving local ecosystem.
Tallamy points out that 85.6% of the land east of the Mississippi River is privately owned. That means homeowners can play an important role in restoring needed insect habitat in their own backyards. As we approach spring in the coming months, many of us are looking forward to tending our gardens. As you plan your plantings, take into account the necessity of supporting native insects by incorporating native plants into your landscaping design. If you reduce the size of your lawn by half, and replace exotic and invasive plants with native species, you will provide much needed habitat. To make the biggest impact, focus your efforts on supporting the insect groups that do the most to maintain plant diversity and to contribute to the food web: pollinators and caterpillars.
Pollinators have two basic requirements that we can address: a reliable food source and nesting sites. Choose a variety of plants that flower during different months so that there is a steady nectar source throughout the season.
The vast majority of our native bees (90% of them) are solitary, nesting either in the ground or inside dead plant stems. In the early spring, have you seen dozens of bees flying close to the ground in a clear area of your yard? Lucky you! Those bees are digging holes where they will place a packet of pollen and lay an egg. Protect those areas during the few days that the bees are active, and you will have lots of native pollinators.
Planted at the base of a tree, native plants like this golden ragwort can provide safe space for caterpillars ready to pupate into moths and butterflies. Photo: Susie O’Donnell
To create a habitat for the bees that normally nest in dead plant stems, some people put up bee “hotels”: structures full of stacked tubes, or pieces of wood with holes drilled into them. Tallamy says that another option is to place simpler bundles of hollow stems throughout your yard. A useful tip is to leave your plants in place instead of clearing away the dead parts when fall comes and they die back. Over the winter, their leftover seeds will provide food for foraging animals, and they will offer bees a natural set of stems for nesting.
Moths and butterflies are another set of pollinators to support. To do this, you have to provide for their caterpillars. (Those caterpillars also support numerous other animals – they are an important food source.) Once they have eaten their fill, 94% of caterpillars bury themselves in soil or leaf litter to transform into moths and butterflies. We can help more of them survive by providing a softer landing place for them under their host plants. Plan your landscaping to protect caterpillars by leaving leaf litter and soft soil under trees, rather than turf or, worst of all, bare ground.
Another way we can avoid killing beneficial insects is by reducing light pollution. You can do this by putting motion sensors on security lights, and using yellow LED lights in them (this cuts down on the number of insects that are attracted to them). It’s also important to eliminate insecticide use on your property. Instead of spraying for mosquitoes, make a mosquito trap by setting out a bucket of water and adding “BTI dunks” once the mosquitoes start laying their eggs in the bucket. (BTI is a bacteria-produced toxin that occurs naturally in soil.)
If you’re unsure what plants are native to our region, the Native Plant Finder website allows you to plug in your zip code and see a list of native plants and trees, ranked according to the number of butterfly and moth species that use them as host plants for caterpillars.
Watch Doug Tallamy’s lecture on the importance of bugs to environmental health.
Good plants to attract pollinators to local backyards:
asters
black-eyed Susan
evening primrose
false indigo
fleabane
goldenrod
sunflower
violets
willow
Native Pennsylvania trees, shrubs, and herbaceous plants that are good hosts for caterpillars:
American elm
black cherry
black gum
evening primrose
goldenrod
green ash
hickory
meadow rue
native clematis
oak
pawpaw
persimmon
red maple
sumac
sweet gum
tulip tree
viburnum
Virginia creeper
walnut
white ash
white pine
witch hazel
Places to shop for native plants:
Redbud plant nursery, Providence Road, Media
Bowman’s Hill Wildflower preserve, New Hope
Brandywine Conservancy’s Mother’s Day weekend native plant and seed sale, Chadds Ford
Scott Arboretum’s plant sales, Swarthmore
Tyler Arboretum’s annual plant sale, Media
Margaret Betz and Susie O’Donnell are members of the Swarthmore Environmental Advisory Council.
