By: Ash Lloyd, EcoHouse Green Gardening Volunteer
If you have a garden, you are probably used to seeing all kinds of bugs on or around your plants during the warm parts of the year. Many people consider bugs they do not recognize to be “gross” or pests, and so when they see them they try to exterminate them! This is a big mistake though – out of the roughly 920,000 known insect species, only 0.5% are categorized as pests to agriculture. This means that if you spray or squash a bug you do not recognize, chances are you killed an innocent bug! This may not seem like a great loss to some, but insects are absolutely critical to the majority of the world’s ecosystems. Unfortunately, they are increasingly under threat in our pesticide ladened environment. With this in mind, let us take a moment to learn about today’s spotlighted insect and gain some insect appreciation!
The Bronze Ground Beetle (Carabus nemoralis)
The Bronze ground beetle (aka “Bronze Carabid”) is an introduced species of relatively large ground beetle that is native to central and northern Europe, where it is quite common. It has also been introduced to Turtle Island (North America) where it is now gradually spreading. Despite being non-native, there is no current reason to be alarmed. Their primary food source are slugs (though it will eat any invertebrate it can catch), many of which are invasive to Canada and are the bane of many gardeners. That means that Bronze Carabids are actually your ally in the never ending battle against those slimy, slithering slugs that feast upon your eggplants and young greens!
The role of the Bronze Carabid is primarily that of a mollusc hunter; they are specially adapted to be able to locate and follow slime trails in order to track down their prey. They are known to eat the young forms and eggs of common invasive pests like the grey slug (Deroceras reticulatum).
They are also great soil churners on the forest floor as they burrow into the ground in search of food and shelter.
It should be kept in mind though that because this species is not native to Turtle Island (North America), it may put additional pressure on native terrestrial mollusc populations. Currently in Ontario, there are three species of terrestrial snails that are under threat from habitat loss:
- Broad-banded Forestsnail [Endangered]
- Eastern Banded Tigersnail [Endangered]
- Proud Globelet [Endangered]
Relationship With Humans
Due to the nature of their diet, they are sometimes known as the gardener’s favorite beetle. It is suspected that if they did not get to Turtle Island by hitching a ride, they were probably brought over in the past 100 years or so as a means to try and better protect crops from slugs.
The Bronze Carabid is often admired for its distinct, bronze-iridescent carapace and relatively large size; an adult Bronze Carabid is roughly the size of the first joint of an adult’s thumb. They are primarily active at night so, unless you yourself are nocturnal, you are most likely to find them while digging or gardening because they hide under dirt and leave litter during the day.
Ground beetles are generally harmless to humans and the Bronze Carabid is no exception. The worst thing it might do if it feels threatened is regurgitate a foul smelling liquid in an attempt to convince you that it tastes bad. Though, I do not think any of us need much convincing not to put it in our mouths.
That concludes this Beneficial Insect Spotlight; I hope you will carry this knowledge with you and pass it on to others. Now that you know about it, hopefully the next time you see this insect, you will admire it with your eyes and not your boots.