Ground beetle, its favorite food is slugs!

Ground beetle with metallic colors

One of the most important beneficial insects in the garden is the ground beetle family. This fearsome predators have a voracious appetite which will certainly serve you well to control pests in your garden.

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All you need to know about ground beetles

The ground beetle group includes the largest ever species of the Carabidae family. Smaller beetles (there are many more of these) are often grouped under the more generic term “beetle”.

Description:

These ground-born beetle insects have a long and flat appearance. They have 3 pairs of legs, which makes them fast-moving hunters and their body has three distinct parts: abdomen, thorax and head. The smallest ground beetles are a quarter inch long or 4 mmTheir size reaches from ¼th inch (3-4 mm) for the smallest species such as the Metallina bembidion (Bembidion lampros) up to nearly two inches (4 cm) for the bronze carabid (Carabus nemoralis). Their shell comes in many different possible colors: green, blue, violet, black, and sometimes they sport metallic-like colors, too.

Even though some individual species have a pair of wings, not many carabids can actually fly. The larvae are fairly unique with their very thin, long body and 6 legs. Before turning into adults, they first go through a chrysalid stage which happens underground.

Biology:

There are two types of reproduction cycles for ground beetles:

  • “Spring” carabids come from larvae that develop over the summer.
  • “Summer” ground beetles come from winter larvae.

Each beetle can live several years. This long lifespan somewhat compensates the fact that they don’t reproduce prolifically.

What does it feed on?

Even though a few species are vegetarian, most of them are clearly carnivores. These very capable predators are able to catch and eat their weight in food every single day! Their diet is varied and they’ll hunt any of the following with gusto: slugs, snails, larvae, aphids, thrips, caterpillars, etc.

Even though they devour large amounts of food, ground beetles won’t be very effective at controlling an invasion of one specific pests such as aphids. Ladybug larvae or green lacewing will be much more targeted and effective. This notwithstanding, they nonetheless greatly help control pest populations in general. This is particularly true for insect species that overwinter on plants or in the leaf litter on the ground: this is the layer between the moist soil and the dry, dead leaves above. Plant materials in the litter layer are in advanced stages of decay.

Habitat:

Ground beetles may find refuge in many places: hedge, strip of grass, under flat stones, in piles of wood, etc.

Usefulness in the garden and vegetable patch

Pest control: ground beetle eating a slugThe main advantage of ground beetles is without a doubt their insatiable hunger: it helps to effectively control pests and parasite populations. Of course, some species might shift to a partly vegetarian diet when there aren’t many other insects. This might cause damage to some plants in the vegetable patch, but it’s very minimal. Moreover, you can solve the problem easily by placing “traps” that will attract ground beetles, like planks, boards or flat stones. During the day, they’ll come hide underneath. All you need to do then is pick them up and place them elsewhere in the garden, where they’ll revert to their more carnivorous lifestyle.

Note that ground beetles are excellent to help control snails and slugs.

How to attract ground beetles to the garden and protect them?

These beetle-like insects are extremely sensitive to changes in their environment. Since they live at ground level, any mechanical tool with rotating blades such as rototillers are apocalyptic calamities for them. Additionally, phytosanitary products might reduce or even completely eliminate this precious beneficial insects’ numbers. The solution is clear: if you want to help your six-footed friends, give them a habitat that is as natural as can be where the human hand only rarely intervenes:

  • Shelter and food will attract and retain ground beetlesa charming wild hedge;
  • a space for wildflowers and wild grasses right in the middle of the vegetable patch, perhaps a dozen square feet or so (a few square meters);
  • a flowered prairie, which will also attract other species of beneficial insects as well;
  • small shelters such as piles of stones, stacks of wood, or heaps of leaves;
  • etc.

Ground beetles are tireless predators, which make them a key help for gardeners. Even though they won’t single-handedly solve your pest problems, they’ll be of great help together with other options, and in any case the services they offer warrant their protection.

Did you know… ? Just like its cancellatus and Pterostichus cousins, the golden ground beetle also feeds on nefarious Colorado potato beetle larva. It is thus a valuable ally when growing potato, and must be particularly well taken care of. Indeed, this wingless species won’t spontaneously come back in a garden it has already disappeared from.


Credits for images shared to Nature & Garden (all edits by Gaspard Lorthiois):
Green beetle by Bernard Dupont under © CC BY-SA 2.0
Small long black beetle by Donald Hobern under © CC BY 2.0
Golden beetle by Dr. Guido Bohne under © CC BY-SA 2.0
Wood with a beetle by Frank Vassen under © CC BY 2.0