Create a ground beetle habitat to encourage biological pest control in your garden

Ground beetles are one of the most species rich groups of insects – there are about 40,000 species worldwide and around 350 species in Ireland and Britain alone. Still, chances are that you might not have noticed them as they are often only active at night but also because many of them are very fast runners that won’t wait around for anyone to get a closer look! Our species range in size from just 1.5mm to 35mm and while many are dark coloured (especially those active during the night), some day-active species are vividly metallic. Not all ground beetle species have functional wings and flight is used mainly for dispersal so most of their life is spent on the ground (hence their name!). Like in butterflies, the life cycle of a ground beetles is egg -> larva -> pupa -> adult with the larvae looking completely different to the adult beetle. It is unlikely that you will find any of these, as they usually live underground.

Larva of the European gazelle beetle Nebria brevicollis

The easiest way to find out which species you might already have in your garden, is to put out a few pitfall traps over night and see what you catch – don’t forget to set them free again afterwards! This earlier blog post shows you how to create one: https://natureathome.org/2020/04/11/bug-hunt/ and this website has photos and descriptions of most Irish and British species: http://www.habitas.org.uk/groundbeetles/taxonlist.html Many common carabids you are likely to find in your garden are great at helping to control common pests such as slugs, aphids or caterpillars and are sometimes described as ‘biological pest control agents’. They have very large jaws called mandibles that make them effective predators – you can see these well in the top picture. They also have a great appetite and are able to eat up to their own body weight in food per day! So just like bees and other pollinators, ground beetles are generally considered to be ‘beneficial insects’ and you should be sure to keep them around and help protect your flowers and veggies from pests.

Two common ground beetle species that you might find in your garden and that will help you with pest control are the Bronze carabid Carabus nemoralis (20-26mm, top) and the Strawberry ground beetle Pterostichus melanarius (13-17mm, bottom). AfroBrazilian / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

To make your garden more attractive for ground beetles (and many other beneficials that will eat your pests like centipedes, rove beetles or spiders), you can offer them undisturbed, dark areas where they can shelter during the day and the winter, such as piles of stones, leaves or dead wood. Details on how you can create these spaces can be found here: https://www.gardenersworld.com/plants/five-habitats-to-make-for-beetles/

For a more permanent structure and a fun project, you can also create a ‘beetle bump’ for your own garden, a miniature version of a beetle bank. These are raised mounds of soil planted mainly with native grasses between or within agricultural fields, that offer the beetles and other beneficials a permanent, undisturbed habitat with dryer conditions in winter and more even temperatures year round. Beetle banks can be several hundred meters long but for the scale of a garden, a ‘beetle bump’ works just fine. By adding a few tall growing wild flowers to the bump, you can also attract pollinators or other predatory insects such as hoverflies and parasitic wasps, but be sure to choose flowers that are able to compete with the grasses. The ‘beetle bump’ is best created in either August/September or between March and May, which are the optimal times for grass establishment. It is important that it is disturbed as little as possible after the grasses are established, especially in winter when most beetles are sheltering. And of course, pesticides should be avoided in your garden as they are often also toxic to the beneficials – and you and your pets!

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