Large black beetles in the house usually appear at night in summer, coming in under doors or from the yard and garden. Most of them do not bite or damage the house, but they are a nuisance and some give off a foul smell when disturbed.
The most common large black beetles
- Slow black beetle (darkling beetle): about 2 to 3 cm long, matt black, walks slowly, and cannot fly because its front wings are fused. When disturbed it releases a foul-smelling fluid.
- Ground beetle: shiny black, fast, comes out at night and is attracted to light; it naturally feeds on other insects.
- Dung beetle (scarab): black and rounded, found near gardens, compost and animals.
Why do they come indoors?
- Lights at doors and windows at night.
- Moisture after watering or rain, or leaks around the house.
- An adjoining garden with piled leaves, stones or compost.
- Gaps under doors and cracks in outer walls.
- Extreme heat, which sends them looking for a cooler, damp place.
Are large black beetles harmful?
- They usually do not bite people or spread disease.
- They do not eat wood or furniture.
- The fluid some species release can mildly irritate skin and leave a smell, so do not handle them.
- Large numbers mean there is a place where they live close to the house.
How to keep them out and get rid of them
- Fit a brush strip or rubber seal under outside doors.
- Reduce lighting at entrances at night, or use yellow bulbs that attract fewer insects.
- Clear the garden of leaves, stones and wood piled near the wall.
- Fix leaks and reduce watering near the house foundations.
- Spray a residual insecticide as a band around the house outside, at doors and cracks.
- Place glue traps inside doors to monitor entry.
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Large black beetle FAQs
Do black beetles bite?
Very rarely. Most species do not bite, and a ground beetle may nip if you pick it up, but it does not attack.
Why do beetles give off a foul smell?
It is a defence mechanism: they release fluid from the rear when disturbed to drive off attackers.
Are small black beetles the same as large ones?
No. Small beetles indoors are usually carpet or pantry beetles and need different treatment. See Small Black Bugs in the House.