Invest in a beetle bank

One of the most important – and yet often overlooked – facets of gardening is its ability to increase backyard biodiversity. And not just within the plant kingdom. When a garden is composed of a wide range of plant material, the animal kingdom also benefits. Especially insects. Most gardeners know that having a diversity of good bugs in the garden means better pollination and fewer pests. While there are thousands of species of beneficial insects in North America, one of the best bugs for your garden is the ground beetle. 

Ground beetles: Slug snackers extraordinaire!

Unless you garden at night, you aren’t likely to encounter this nocturnal beneficial insect on a regular basis, even though ground beetles are extremely common – there are over 2,000 species in North America alone. Each species looks different, of course, but most ground beetles are dark and shiny with ridged wing-covers. They hide in grasses or underneath objects during the day, so if you flip over a rock or a log and see a dark beetle scurrying around, there’s a very good chance it’s a ground beetle.

Ground beetles are such good bugs in the garden because they scour the garden for prey all night long. Both adult and larval ground beetles consume mites, snails, slugs, caterpillars, earwigs, cutworms, vine borers, aphids, and lots of other insects. Each beetle can eat more than its own body weight in prey insects every night (bye-bye slugs!). In my opinion, of all the good bugs in the garden, these seldom seen critters are the cream of the crop.

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Welcoming ground beetles

Many insects are specialized both in terms of their food needs and their habitat preferences. Smart gardeners use this to their advantage, installing certain plants in order to support a particular insect. You may already have milkweed to support larval monarchs, dill for the swallowtails, mountain mint for the native bees, or fennel for the ladybugs. These examples are just a small part of a very long list of plant/insect partnerships that can be easily fostered by making a few thoughtful choices. One such partnership exists for pest-munching ground beetles, too.

Because ground beetles like to take shelter in grasses during the day, building a specialized habitat known as a beetle bank is the best way to encourage this beneficial insect.

How beetle banks encourage more of these good bugs in the garden

A long-standing practice of farmers in Great Britain and Australia, beetle banking creates the perfect habitat for ground beetles. Beetle banks are elongated, permanent, raised berms, positioned throughout crop fields. They’re planted with the native bunchgrasses ground beetles love to take shelter in.

Ground beetles like to climb upwards and away from moisture, so the berms are mounded 12 to 18 inches high. The native bunchgrasses planted on the berm provide ideal daytime habitat, and when night falls, the beetles move out into the fields to forage for prey.

On farms, beetle banks are four- to eight-feet wide and run the entire length of a crop row, but for home gardeners, the scale is obviously much smaller.

Build a small-scale beetle bank using these steps:

1. Select the location. If you don’t have room to put a beetle bank inside of your actual vegetable or flower garden, locate it a few feet away. Unlike some other good bugs in the garden, ground beetles will travel a good distance to find prey, but the closer it is to the garden, the better.
2. Select the shape. You can go with a “classic” berm-shaped, two- to four-foot wide beetle bank, or if you don’t have that much room, another alternative is to create one or more beetle “bumps” instead of a bank. These are raised, circular areas in the lawn or garden that don’t have to be any particular size (though they should be at least four feet across); they just need to fit in with your landscape and remain undisturbed.
3. Mound the soil. Whether you’re creating a bank or a bump, begin by mounding soil over the area until it’s 18 inches high (it will settle over time).
4. Plant it. The entire area should be planted with a minimum of three different species of native bunchgrasses. There are many grass species that fit into this category, but all grow into a clump or tuft, rather than spreading horizontally to form a sod-like mat. Prairie dropseed, switch grasses, gamagrasses, feather grasses, muhly grasses, bluestems, and indian grasses are a good place to start.
5. Maintain your beetle bank or bump. You’ll need to water the area until the grasses are established, and keep it weeded. But, other than that, there isn’t much maintenance required. Every year, after the grasses have gone to seed in the late fall, the area should be trimmed or mowed to a height of six to eight inches. Leave the clippings in place as they’ll create winter habitat for your ground beetles.

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Other beneficial insects live there, too

Research also shows that ground beetles aren’t the only beneficial insects that take shelter in these banks or bumps. Pest-eating rove beetles, tiger beetles, ladybugs, spiders, and lots of pollinators, such as native bees, are also regularly found in beetle banks.

As you can see, beetle banks are a great example of how backyard habitat creation can promote insect biodiversity and help gardeners get a grip on pests. Install a beetle bank or bump, and watch these good bugs in the garden do their thing!