Ground beetles, predators of slugs: how to attract them to the garden?
“It’s all very well working on a slug management system, Mr Robin Springday, but Nature knows how to handle the problem on its own!”
Quite right!
And do you know how?
In particular, through the natural way predators are drawn in when prey is abundant!
I’ve already written an article on hedgehogs, one on amphibians, one on leopard slugs…
So what about ground beetles?
Ground beetles are ground-dwelling predators that specialise in preying on slugs and snails (some have even developed a particular hunting technique).
As with hedgehogs and amphibians, knowing how to lay out your garden to attract ground beetles and settle them in is a big plus for helping to regulate the slug populations that swarm there in spring.
What I’m suggesting in this article is that you get to know ground beetles and their habitat, so you can see how to set the garden up accordingly. I’ve also slipped in a little video riddle that you can show your friends to see whether they know a thing or two about the life in their garden.
One last thing: did you know that the presence of ground beetles in the garden reduces the spread of often-invasive plants (sometimes labelled “weeds”)?
Off we go!
If you're discovering my blog, chances are slugs and snails are giving you grief.
You'd probably be very interested in the copper slug barrier I designed .
It changed everything for me. I can finally grow lettuce, cabbages, strawberries and squashes without tearing my hair out.
Don't hesitate — it's an investment (copper is expensive), but you'll likely save yourself a huge amount of time!
Before we begin, if it interests you, here’s the article on all the predators of slugs.
I. The ground beetle: meet a slug predator
1. A few facts about ground beetles to get started
The ground beetle is a predatory ground-dwelling insect, active mainly at night.
It hunts in low vegetation.
Its family (the carabids) is made up of more than 40,000 different species!
In France, the golden ground beetle and the wood ground beetle are said to be the most common (according to some sources), but there are dozens of different species: indeed, the barely noticeable anatomical differences between each species can make it hard to identify each one. It’s easy to get it wrong by associating every specimen with golden glints with the “golden ground beetle” (Carabus auratus), and every “matt” specimen with the “wood ground beetle” (Carabus nemoralis).
The presence of the ground beetle has been judged a good indicator of the biodiversity of the environment where it’s observed. So if you have some in your garden, that’s a good sign!
Another little fact: ground beetles have two development cycles:
- There are the spring ground beetles: the adults mate in spring, then lay eggs and the larvae hatch during spring and summer, and the larvae turn into adults at the end of summer.
- And there are the summer ground beetles: the adults mate during summer, lay eggs in autumn, and the larvae hatch and turn into adults in spring.
The summer ground beetles have a development cycle that coincides very neatly with the peak period of spring slug populations.
Worth noting too: ground beetles have a lifespan of 2 to 3 years, on average.
A video offering a look at several species of ground beetle:
2. What do ground beetles eat?
The vast majority of ground beetles are carnivorous. The adult is fond of slugs and snails, but not only that… (aphids, insect eggs, larvae, worms, springtails, ants, spiders, etc.). The larva, for its part, feeds on insect eggs, larvae, worms, and small insects. Diets can vary depending on the species. The golden ground beetle, for example, is the only species that goes after Colorado potato beetle larvae.
For those who doubt that ground beetles like slugs, take a look at the video below!
Ground beetles use their mandibles to kill and crush their prey. They then inject it with a fluid rich in digestive enzymes, the purpose of which is to pre-digest the prey before swallowing it.
The ground beetles most specialised in hunting gastropods have a very particular method of attack: they immobilise the slug by biting it, which is said to prevent it from producing the mucus it would use to defend itself.
These gentlemen ground beetles feed copiously, because they need to consume their own body weight in food every day! Nothing beats a nice orange slug to fill the stomach properly! 😉
Certain species of ground beetle (Harpalus spp., for example) are seed-eating, and that is also of considerable importance in organic farming (more on that in what follows!).
3. Ground beetles as an effective means of biological control against “weeds”
A joint study by INRA and the BBSRC indicates that the presence of seed-eating ground beetles in cultivated fields is an effective way for farmers to fight the spread of “weeds”.
The ground beetles of this species do indeed seem to have a preference for the seeds of plants regarded by farmers as “weeds”, plants that therefore compete with the crops grown on the plots.
With each seed-eating ground beetle consuming from one to several dozen seeds per day, the seed loss caused by a ground beetle population’s feeding is reportedly 50%, which is enormous.
Managing seed-eating ground beetles intelligently (and above all preserving them!) near cultivated areas proves to be a very interesting alternative to herbicides, which are still used far too often.
If you’re interested in learning more about this, here is a two-hour thesis defence that addresses this topic of weed-seed regulation by ground beetles (I admit I didn’t watch all of it):
II. How to attract the ground beetle to the garden in order to regulate slugs?
1. Where do ground beetles live?
Ground beetles live mainly under tree bark, in wood debris, under stones, among dead leaves, in hedges, or in brushwood.
In winter, they hibernate snugly in a stump or a bank.
Ground beetles have a “ base camp ” from which they sometimes venture several dozen metres (up to 70 m for the golden ground beetle, for example) to hunt.
Beds of low vegetation, as already mentioned at the start of the article, make up their main hunting ground (they go mainly after ground insects). For this reason (and perhaps for others, but that’s unclear), beds of red clover seem to favour its presence.
Phacelia beds, for rather obscure reasons, also seem to attract them.
2. Laying out the garden to attract ground beetles
If you want to attract ground beetles to your garden (to help regulate slugs, for instance), it’s best not to have a garden that’s “too tidy” (as with attracting most insects and animals). Piles of wood or branches, dead leaves, old stumps, or stony corners will delight them. A hedge with its base carpeted in dead leaves is a very good start, which also pleases most beneficial insects and animals. Insect shelters with large cavities in direct contact with the ground can also make good shelters.
Maintain low vegetation that’s rarely mown, and ground beetles will fall in love with you and your garden.
Plant beds of red clover and phacelia, and they’ll make a religion of you.
Don’t forget that letting slugs live within your garden is also something essential to their presence: predators are drawn in by prey, and a continuous food supply makes a place favourable for settling in (a “base camp”).
3. What to avoid when you want to attract ground beetles to the garden
Careful — laying out the garden is great!
But you also have to take care not to harm them through other means.
A very important thing is to avoid ploughing the soil with modern, destructive machinery, because the ground beetle is often found there too.
The second important thing is to ban the use of beer traps. Quite apart from the fact that they’re counterproductive for solving a slug population for good, the smell of (drowned) slugs attracts ground beetles, and it’s common for ground beetles to fall into the beer container and drown in it.
These precautions, plus the measures mentioned above, and your garden will be a veritable Eden for ground beetles :p
III. Aside from attracting natural predators, what other solutions are there for the intelligent regulation of slugs in permaculture?
Attracting the predators of slugs, as stated in this heading, is one of the first steps leading to this natural regulation of the problem. The key being to let slugs live within the garden, in order to attract these predators naturally.
Be careful, too, not to confuse natural predators (hedgehogs, amphibians, ground beetles) with adopted predators (Indian runner ducks against slugs, nematodes) (click on the predator to access the article in question), which for their part don’t naturally take part (in these proportions) in the ecosystem, and whose presence prevents the natural predators from settling in (very unfavourable competition for food, because these predators are veritable slug-extermination weapons, and also (in the case of the Indian runner duck) of other insects).
The second point is the choice of suitable plants when laying out the garden: I’ve written a series of articles on this, which you’ll easily find by browsing my site.
The third point consists in giving the garden time to “mature”, generally speaking (for “young” gardens), and letting the soil fungi develop.
And, if you can’t wait, using effective slug barriers is a very good way to save your crops while you wait for the problem to regulate itself naturally.
Done with slugs. For good. Starting this season.
If you don’t want to enter your email because you’re afraid I’ll pester you, you can also gather this information for yourself by digging around a bit in the “slugs” section of my site 😉 (you’ll find absolutely everything there)
Conclusion:
Here’s a short video that quickly recaps everything we’ve just covered!
It’s a video riddle. For you, who have read the article, you of course already know what it’s about. But you can show it to your friends to see whether they know a thing or two about the life in their garden! And to spot any slowcoaches! :p
Increasing the overall biodiversity of your garden very often helps to avoid many problems with little “pests”.
For slugs, that’s the case too, and attracting their natural predators is a very good way to achieve lasting regulation of a slug problem.
The ground beetle is a renowned predator of slugs, and its presence in a permaculture garden really is a stroke of luck.
In this article, we’ve seen what small garden adjustments it might be possible to make to attract it and encourage it to settle in.
Hoping this helps you gradually understand the interdependencies that exist within our little garden-systems, and why not also take a step towards solving your slug troubles for good!
The information in this article has been selected and verified according to the criteria defined in our editorial charter.
Scientific bibliography
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