Bugs in the woods

Forests are complex, intricate and nuanced—and also massive, expansive and interconnected. To be responsible forest stewards we need to both zoom out to understand our role in a giant landscape and zoom in to recognize the tiny pieces and parts that make forests work. We must (somehow) hold both realities in focus as we take care of our forests.

Giant ichneumen wasp by Gary Sturgis
Giant ichneumen wasp by Gary Sturgis

This month I want to zoom in to talk about invertebrates. Simply put, invertebrates are organisms without spines, an incredibly diverse group of critters that includes everything from insects to sea sponges, squids, slugs and worms. What most people call “bugs” are arthropods, a sub-group of invertebrates that includes insects, spiders and even lobsters.

Invertebrates are an incredibly adaptive and resilient bunch, having been around since before the dinosaurs. In terms of sheer abundance and diversity, they stand alone: of the approximately two million known species on earth, about 97 percent are invertebrates (900,000 species are just insects), with somewhere between eight million and 30 million species still undiscovered. Besides accounting for a huge proportion of our biodiversity, the sheer amount of bugs on earth is startling: there are around 200 million insects for every human on the planet, about 300 pounds of insects for every pound of human. To put this in perspective, the combined mass of all the humans on earth is about equal to that of all the ants, or the mass that all the spiders on earth eat in one year.

In Vermont, there are more than 20,000 known species of invertebrates, compared to 58 species of mammals. These invertebrates support our ecosystems in countless ways, mostly unseen. They are what biologist E.O. Wilson calls “the little things that run the world,” subtly working behind the scenes to make our world work.

Invertebrates are the base of the forest food web, directly and indirectly feeding larger wildlife. Moth and butterfly caterpillars, for example, are critical sources of protein that songbirds rely on to feed their young in the spring. Caterpillars and other bugs often have close, co-evolved relationships with one or a few different tree species, and so diverse forests are critical to providing habitat for them and the species that eat them.

Invertebrates are also decomposers, turning organic material like wood into soil. Soils are largely biological in nature—their physical and chemical composition a result of being passed through the bodies of countless tiny organisms, transformed by mites, springtails, nematodes and more. A handful of forest soil may contain thousands of invertebrates of hundreds of different species, not to mention millions or even billions of organisms, if you include bacteria, protozoa, algae and fungi.

Invertebrates perform a huge number of other essential functions. Some—especially flying insects like flies, beetles, or Vermont’s more than 300 species of native bees—are pollinators, helping more than two-thirds of Vermont’s plant species reproduce. Others, like ants, disperse the seeds of some of our native spring wildflowers. The list goes on.

Not all is good with bugs in the woods. Some invertebrates are non-native tree pests, such as the emerald ash borer (EAB) and hemlock wooly adelgid (HWA). Some non-native bugs that are celebrated in agriculture—the Eurasian honeybee and earthworms—can be problematic in our ecosystems. Non-native invasive plants like honeysuckle, buckthorn and barberry take over forests, providing habitat for only a tiny fraction of our invertebrates. For many reasons, invertebrates are going extinct at an incredibly fast rate, with as many 100,000 species lost since the 1600s and 40 percent of known invertebrate species thought to be under threat of extinction.

Invertebrate habitat is as diverse as they are. They live in rotting wood, in soil, in the leaves and branches of young, healthy trees and the complex bark of big, old trees. On a large scale, the most important thing we can do for invertebrates is to protect our forests from fragmentation and loss, managing for diverse, intact, connected landscapes. On a smaller scale, we can manage for complex forests, encouraging different sizes, ages and species of trees while also leaving some big “legacy” trees, dead-standing trees, and lots of dead wood on the forest floor, and dealing with biodiversity threats like non-native invasive plants.

Great things come in small packages. As strange as it seems, healthy populations of bugs are critical to the integrity and the resilience of our forests and the beauty and function of our world.

Ethan Tapper is the Chittenden County Forester for the Vermont Dept. of Forests, Parks and Recreation. See what he’s been up to here.