Insects and Pollinators

Most of Wisconsin’s animal life, by count of species, is insects, and the ones people notice most are the pollinators. This lesson covers the bees, which outnumber the birds; three insects whose stories say a lot about Wisconsin’s landscapes; and the practical things that help.

Bees that live alone

There are about 400 bee species known from Wisconsin ¹. Two kinds live in colonies: honey bees, which were brought from Europe and are kept like livestock, and the native bumble bees. Nearly all the rest are solitary: each female builds and stocks her own nest, with no colony to defend, which is why they’re docile ¹. Some native bees pollinate particular crops and wildflowers better than honey bees do ¹.

Most of them nest underground. About 70% of the world’s bee species dig their nests in soil ². In early spring, look on a sunny, south-facing slope of sandy soil with thin grass: mining bees and cellophane bees can nest there by the thousands, each hole a little bigger than an ant hill’s with a fuzzy face sometimes peeking out ². Each female digs a main tunnel and 5 to 10 side chambers, stocks each with pollen and nectar, and lays one egg in it. The males emerge about a week before the females and patrol the nesting area; males can’t sting, and the females rarely do ².

The rest nest in hollow chambers: old beetle tunnels in dead wood or the pithy, hollow stems of last year’s plants ¹.

Bumble bees

Twenty bumble bee species have been found in Wisconsin, now or historically. One is federally endangered, seven more are state species of greatest conservation need, and three more are flagged because too little is known about them ³.

The endangered one is the rusty patched bumble bee. It was once common across the eastern U.S. and upper Midwest, then crashed so steeply that it was listed in 2017 ⁴. The cause isn’t certain, but the evidence points to an introduced disease combined with pesticide exposure, on top of habitat loss ⁴. Workers have a small rusty-brown patch in the middle of the abdomen.

Because so much is still unknown, including where the bees spend the winter, the DNR runs the Wisconsin Bumble Bee Brigade: volunteers catch, photograph, and release bumble bees on regular surveys to map the species and track their trends ³.

The monarch

Monarch caterpillars eat only milkweed. The plant’s toxins build up in their bodies and make both caterpillars and adults taste bad to predators, which is what the bold orange and black advertise ⁵. Adults need nectar from a long run of flowers from spring through fall.

The eastern population, the one that breeds in Wisconsin, makes the famous migration: each fall they fly more than 2,000 miles to overwintering forests in the mountains of Mexico ⁵.

Monarchs have declined more than 80% since the 1990s ⁶. The Fish and Wildlife Service proposed listing them as threatened in December 2024, but the decision was delayed. Under a settlement reached on September 30, 2026, the final decision is now due by June 6, 2030 ⁶. Milkweed in a yard, field edge, or road ditch matters in the meantime.

The Karner blue

The Karner blue is a small butterfly, an inch across, and Wisconsin has the largest populations in the world ⁷. Its caterpillars eat only wild lupine ⁷, a blue-flowered plant of sandy oak savannas and pine barrens, so the butterfly lives where lupine lives, mostly in the sandy country of central and northwestern Wisconsin.

Lupine needs open, sunny ground. Those savannas and barrens were kept open by fire. When fire is kept out, shrubs and trees move in, shade out the lupine, and the butterflies are left in small, isolated patches that can blink out ⁷. That’s why Karner blue habitat is managed with prescribed burns and brush cutting, and why the DNR runs a statewide Habitat Conservation Plan partnership with landowners and land managers to keep lupine growing in sunny openings ⁷.

The emerald ash borer

Not every insect story is about losing a native. The emerald ash borer is a metallic green beetle from Asia. It was first found in Wisconsin in Ozaukee County in 2008, and by 2024 it had been confirmed in all 72 counties ⁸. Its larvae carve winding S-shaped tunnels under ash bark, cutting off the tree’s water and food. The canopy thins from the top down, woodpeckers flake off the outer bark hunting larvae, and the tree dies. More than 99% of Wisconsin’s white, black, and green ash are expected to die ⁸.

It spreads on its own only slowly; it gets around mainly on firewood ⁸. That’s the simplest rule for all forest pests: buy or cut firewood near where you’ll burn it.

What helps

Every one of these stories comes back to a few things you can do on any yard, field edge, or woodlot:

• Flowers from April through October, so something is blooming whenever bees are flying. Natives like wild bergamot, asters, goldenrods, and milkweed carry a lot.
• Bare, sunny ground. Leave a patch of sandy soil unmulched and unmowed-down for ground nesters.
• Stems and dead wood. Leave last year’s hollow stems standing until late spring and keep a snag or log pile.
• Lupine and fire where the soil is sandy, and milkweed wherever it’ll grow.
• Local firewood, always.

In short

Wisconsin’s 400-odd bees mostly live alone and underground. The rusty patched bumble bee is endangered and the Bumble Bee Brigade is mapping the rest. Monarchs need milkweed and fly 2,000 miles to Mexico, with a federal decision now due by 2030. The Karner blue needs lupine kept open by fire, and Wisconsin holds its biggest populations. And the emerald ash borer, in every county now, is a reminder of why firewood shouldn’t travel.