On March 22, 2022, Doug Tallamy gave an information-packed presentation documenting declining insect populations and implications for other species (including humans!), but offered tangible suggestions for actions we can take to reverse this trend. Doug Tallamy, PhD, is the T. A. Baker Professor of Agriculture in the Department of Entomology and Wildlife Ecology at the University of Delaware, where he has authored 104 research publications and taught insect-related courses for 40 years.
The following post condenses and summarizes his presentation, but we strongly encourage you to watch his presentation here (or at the end of this summary), because it contains MUCH more invaluable information. Some of the sources in Doug’s presentation can be found at the end of this post, along with resources relating to selecting and purchasing native plants appropriate to your site, and naturalizing land areas.
E.O. Wilson, well known biologist, wrote a paper in 1987 hypothesizing about what would happen if insects disappeared. He concluded that most flowering plants would disappear (because they’re pollinated by insects), the food web that supports amphibians, reptiles, birds, mammals, etc. would quickly collapse, and the biosphere (living part of the world) would rot due to the loss of insects that consume dead plant and animal matter.
Historically and culturally, we have viewed all insects as ‘bad’ and haven’t worried about losing them. In fact, we have actively tried to eradicate them. If we do recognize value in insects, we assume they continue to thrive in natural areas, not recognizing that we have relatively few ‘natural areas’ left. Agricultural land occupies almost 50% of the earth’s surface, with the balance occupied by cities, suburbs, and many rural areas that don’t provide great insect habitat.
Remember having to clean your windshield of insects? When did you last have to do that? Unfortunately, we are winning the war against insects. In recent decades, scientists finally began to study insect populations and are documenting significant insect decline: 79% insect decline since 1989 in Germany; 45% decline in invertebrate abundance globally since 1974.
As insects decline, so do the things that eat them. For example, birds – there are three billion fewer breeding birds today than 50 years ago. Most baby birds require insects as food. If you take away their food, you take away birds.
Birds migrate to take advantage of the historically abundant food supply in northern climes in spring (peak caterpillars feeding on new leaves). The abundant food fuels increased offspring. When migration evolved, there were lots of insects. That has changed.
Exotic plants, introduced because they were ‘pest’-free, escaped from gardens and are replacing native plants in our landscapes. These exotics support far fewer insects. Carolina chickadees need 6,000 – 9,000 caterpillars to fledge a single nest of baby birds. They can’t travel far to search for food. If all they have access to is a sterile lawn and ornamental, non-native trees, they won’t find food.
Insect decline is a result of death by a thousand cuts, principally pesticides, habitat loss, plant choice, invasive species, light pollution, and climate change. Almost all of these can be addressed by action at the individual level.
We have to incorporate ecological goals into how we manage our landscapes. It is possible to choose beautiful plants that also support food webs. When we do this, we should prioritize the two most important insect groups: pollinators, because they pollinate 80% of all plants; and caterpillars, which transfer more energy from plants to other animals than any other insect.
Since there is lots of information about plants that support pollinators, we’ll focus on caterpillars which requires a brief biology lesson….
Plant’s don’t want to be eaten, so they load their leaves with nasty compounds – chemicals that don’t taste good. Over long periods of time, insects have evolved highly specialized adaptations that enabled them to eat specific plants. They can eat only those plants. The most familiar example of this is monarchs and milkweed, but many other insects are similarly limited to a single plant. So-called insect specialists represent a majority of plant-eating insects.
Five percent of our native plants support 75% of the insects that drive the food web. Oak is the most productive tree in the country in terms of supporting caterpillars. The National Wildlife Federation has a native plant finder (see Resources below), searchable by zip code, that lists native plants which host the most caterpillar and moth species (including the names of those caterpillars and moths).
Doug offered a fun challenge to adults and children. Go find a paddle caterpillar – which feeds on leaves of alder, apple, birch, blueberry and huckleberry, cottonwood, dogwood, elm, hazel, hickory, maple, oak, and willow – and figure out what it uses the paddles for.
Doug has seen the difference that restoring native plants to the landscape can make, because he did it on his own property. When he and his wife bought their house in Pennsylvania, its 10-acre lot was a hayfield. They planted native trees, shrubs, and groundcovers, and tolerated native volunteers that ‘have a bad rap’ or are considered weeds by some (e.g. poison ivy, grapes, goldenrod), with stunning results.
Today, the Tallamy property supports 1,140 moth species, and because they have moths (and their precursor caterpillars), they have birds in abundance. They have documented a mind-blowing 60 species of birds breeding on their ten acres, including Woodthrush, a forest-dwelling species (that is in decline), because the trees are now tall enough to attract it. As Doug states, “We increased biodiversity on the property by more than two-thirds, it didn’t take that long, and it wasn’t that hard.”
Here are nine things you can do on your property (or help a friend on theirs) to increase habitat for insects and the many creatures they support:
- Cut your lawn in half (40 million acres of lawn in the U.S.). Lawn is an ecological desert and does not sequester carbon. Meadow does sequester carbon.
- Plant for specialist bees
- Remove invasive plants
- Use keystone plants
- Landscape for caterpillars
- Reduce light pollution (use a motion-sensing light and a yellow LED lightbulb)
- Oppose mosquito spraying
- Minimize use of insecticides
- Don’t use bug zappers
Doug had many practical suggestions, including:
- Leave leaf litter under trees and plant native shrubs and groundcovers under them. The trees and insects will benefit.
- Use the bucket technique (described in his talk) to control mosquitoes at their larval stage (most effective), which uses BT (Mosquito dunk) and is very targeted.
- Let your lawn grow out and use mowed paths to avoid ticks. Be particularly mindful of ticks in May and June.
- Visit your local nursery and tell them you want to buy straight species, grown from seed (not clones), not cultivars (especially those that change flower shape, color, shrub/tree leaf color, etc).
- Buy native plants grown from seed to preserve genetic diversity. We need genetic variability.
- Advocate with your town to avoid spraying.
- Use BT for browntail, not abamectin (systemics last several years and kill everything).
- Use fake paper wasp nests to deter wasps from building nests around your house.
- To maintain meadow, mow or burn one-third each year to leave habitat for insects.
- To control invasives, cut the stem to the ground and paint the cut stump with pesticide. Look for detailed info on specific invasives for best timing.
As E.O. Wilson describes in his book Half-Earth, we need functioning ecosystems on half of the earth in order to support humans and other creatures, long-term. Today, half of the earth is agricultural land, with cities, suburbs, and humans occupying a great deal of the other half. This needs to change.
The good news is , we can all start where we live. We don’t have to do it everywhere, just on the piece of the planet that we control.
Native plant finders
- National Wildlife Federation’s Native Plant Finder: https://www.nwf.org/nativeplantfinder/. Enter your zip code to access lists of native plants that support the highest number of caterpillar and moth species (and the names of those caterpillars and moths)
- National Wildlife Federation: Keystone native plants, by region
- Wild Seed Project (Maine) – native seeds and annual native plant sale, plus extensive information on their website about rewilding, how to start natives from seeds, plant finders which you can filter based on site conditions, workshops, etc.
- Maine Audubon also has a native plant finder and information about their annual native plant sale that begins June 11.
- Native Plant Trust – sells native plants for pick up in Massachusetts. Also has a native plant finder that you can filter by access to sunlight, soil moisture, and other criteria
- Campo di Fiori is a nursery in Bowdoinham that has beautiful plants. Not all are native, but the owner does have some local offerings that have been propagated from local genetic stock that has been conscientiously harvested from the wild.
- Cooperative Extension has informational handouts on individual natives and information about invasive plants. See Plants for the Maine Landscape.
- Yardscaping info from the State of Maine.
- Homegrown National Park – Doug Tallamy’s website where you can sign up to add your property toward the goal of 20 million naturalized acres.
- Fake paper wasp nests from Gardeners Supply
- Native plant Facebook groups: Native Plants of New England, Garden Native (Northeast), Native Plants of the Northeast (some are private and you must apply to join)
- Garden Revolution, by Larry Weiner
- Invasive Plant Field Guide available from the Maine Natural Areas Program, along with fact sheets about individual invasive species, including information on how to manage or eradicate them.
Sources cited in D. Tallamy presentation
- Burton 2017 (decline of Europe’s grasshoppers etc)
- Halman et al 2017 (documenting insect decline)
- Dirzo et al 2019 (documenting insect decline)
- State of the Birds 2016
- David Rosenberg et al, 2019 (documenting loss of three billion breeding birds since 1970)
- The Insect Apocalypse Is Here (NYT, 11/27/18)
- One million species face extinction UN panel says humans will suffer as a result (Washington Post, 5/6/19)
- Nyfeller et al, 2018 (birds eat 500 million tons of insects each year)
- Richard et al, 2018 (Biological Invasions)
- Janzen, 1988 (caterpillars transfer more energy from plants to animals than any other insect)
- Forister et al, 2014 (90% of insects that eat plants can only eat the plants with which they have an evolutionary history)