Moisture Bugs: How to Identify the Species and Eliminate the Problem
A silvery insect in the bathtub, little grey bugs rolling into balls in the basement, tiny white specks hopping around your houseplants? You are probably dealing with moisture bugs, also called humidity insects. They are among the most common household pests in Quebec, especially in poorly ventilated rooms or areas prone to water infiltration. The good news: in most cases, identifying the species and fixing the humidity problem is enough to solve it for good, without harsh chemicals. Here is how to recognize them, where and why they show up, how to get rid of them and when to call a professional.
Identifying your moisture bugs
Before choosing a solution, you need to know what you are dealing with. These are the species most often found in Quebec homes.
Silverfish
Silverfish are silvery grey, wingless and about 1 to 2 cm long. They move very fast with a fish-like wriggle and avoid light. You will find them in bathrooms, basements and kitchens where humidity runs high. They feed on starchy materials (paper, glue, textiles) and can damage books, wallpaper and clothing if left unchecked. They are not a health hazard.
Earwigs
Earwigs have a long, reddish-brown body with pincers at the tip of the abdomen. They are nocturnal and like dark, damp spots: basements, bathrooms, gardens and under mulch. They are harmless to people, but seeing many indoors means there is too much moisture; chewed leaves on houseplants are often the first sign. Our guide on how to get rid of earwigs covers the solutions in detail.
Sowbugs and pillbugs
Sowbugs are not insects but land-dwelling crustaceans, related to lobsters and crabs. Their oval, segmented body is slate grey, and pillbugs roll into a ball when threatened. They live in basements, bathrooms, garages and under sinks, feeding on decaying organic matter. They are harmless to you and your home, but they are a clear sign that indoor humidity is too high.
House centipedes
With its long body, many legs and startling speed, the house centipede makes plenty of people jump. Yet it is an ally: it hunts spiders, cockroaches and other small pests at night. You will mostly see it in the basement and bathroom. It is not dangerous to people; if you keep seeing it, it mainly means its prey are living in the house too. Slow, round-bodied millipedes are also common near foundations and just as harmless.
Book lice (psocids)
Book lice are tiny, barely visible, soft-bodied and pale. They live in very damp, mouldy spots: basements, attics, damp walls. Because they feed on mould, their presence often points to hidden mould. They are harmless to people but can damage books and papers stored in damp areas.
Springtails
Springtails are tiny white or grey insects that jump using a forked tail folded under the abdomen, which is why they are often mistaken for fleas. They live in soil, leaf litter, houseplant pots and very damp areas such as bathrooms, feeding on fungi, algae and decaying matter. Harmless, they become a nuisance when they show up by the hundreds.
Carpenter ants and cockroaches: two special cases
Carpenter ants, large black or bicoloured ants, are drawn to damp or damaged wood around windows, roofs, sinks and foundations. They do not eat wood; they hollow it out to nest, which can weaken the structure. Watch for fine sawdust, rustling in the walls and winged ants in spring.
Cockroaches are the biggest health concern on this list. They thrive in damp kitchens, bathrooms and basements, can carry pathogens and contaminate food. Look for small black droppings, egg cases (oothecae) and a persistent musty smell. Both of these pests almost always require professional treatment.
| Pest | Size | Where you find it | Harmful? |
|---|---|---|---|
| Silverfish | 1–2 cm | Bathroom, basement, kitchen | No, damages paper and fabric |
| Earwig | 1–2 cm | Basement, garden, bathroom | No |
| Sowbug | 1–2 cm | Basement, garage, under sinks | No |
| House centipede | 2–4 cm | Basement, bathroom | No, eats other pests |
| Book louse | under 1 mm | Basement, attic, damp walls | No, sign of mould |
| Springtail | 1–2 mm | Plants, bathroom, soil | No |
| Carpenter ant | 6–13 mm | Damp wood, windows, roof | Yes, structural damage |
| Cockroach | 1–4 cm | Kitchen, bathroom, basement | Yes, health risks |
Where you find them and why: room by room
Where you spot the bug is often the best clue to identify it and track down the moisture source.
In the bathroom
The bathroom is the most vulnerable room: the shower, tub and sink produce steam that collects in grout, behind tiles and under cabinets when ventilation falls short. Silverfish, sowbugs and house centipedes are the usual suspects. Run the exhaust fan during every shower and for at least 20 minutes after, and check the caulking around the tub and shower: cracked or blackened caulking lets water straight in.
On the walls
Bugs crawling on walls, especially at night, usually mean there is moisture inside the wall: water infiltration, a thermal bridge causing condensation or a hidden plumbing leak. Silverfish and house centipedes are the most common culprits. If dark stains appear at the same time, it may be mould: have the area inspected before treating.
In the basement
In direct contact with the ground, basements are prone to rising damp and seepage through the foundation, often with poor ventilation. They are home to sowbugs, earwigs, house centipedes, springtails and book lice. A properly sized dehumidifier and sealing foundation cracks are the first two steps.
Tiny bugs that are hard to identify
No bigger than a grain of sand? They are most likely springtails or book lice. Both appear in large numbers all at once, often after a very humid spell or a leak. Springtails jump when disturbed; book lice do not. Either way, the fix is the same: lower the humidity and remove sources of mould.
Why humidity attracts these pests
Moisture bugs need water to survive and breed, and several feed on the mould that grows in damp spots. When relative humidity regularly tops 60%, your home becomes ideal for them, and for mould. Health Canada recommends keeping relative humidity between 30% and 50% to prevent mould; it is also the best target against these pests.
So the bugs are rarely the real problem: they are a symptom of water infiltration, a leak or poor ventilation. Treating the bugs without fixing the moisture is like bailing out a boat without plugging the hole.
Home remedies to get rid of them
For most moisture bugs (cockroaches and carpenter ants aside), simple remedies do the job, as long as you deal with the humidity at the same time.
Diatomaceous earth
This natural powder, made from fossilized algae, damages the outer shell of insects that crawl through it and dries them out. It works on silverfish, earwigs, sowbugs and springtails. Dust a thin layer along the walls of affected rooms, into cracks and near entry points. It stops working once it gets wet, so pair it with a dehumidifier in very damp rooms.
White vinegar
A 50/50 mix of white vinegar and water cleans off the mould and algae that springtails and book lice feed on. Its smell also disrupts ant scent trails. Use it on window sills, around sinks and in bathroom grout.
Homemade earwig trap
Fill a shallow dish with soy sauce and a few drops of olive oil. The soy sauce attracts earwigs and the oil keeps them from climbing out. Set it where you see them, empty it every morning and repeat until they become scarce.
Essential oils, as a complement
A few drops of peppermint, lavender or tea tree oil diluted in water and sprayed near entry points repel some species, mainly ants and silverfish. The effect stays limited if the humidity is not fixed.
| Remedy | Target pests | Effectiveness |
|---|---|---|
| Diatomaceous earth | Silverfish, earwigs, sowbugs, springtails | High |
| White vinegar | Springtails, book lice, ants | Medium, mostly preventive |
| Soy sauce trap | Earwigs | High for this species |
| Essential oils | Ants, silverfish | Low to medium, complement only |
Prevention: reduce humidity at the source
Improve ventilation
In bathrooms and kitchens, always run the exhaust fan while producing steam and for at least 20 minutes after. A fan that is too old or too noisy to use regularly is worth replacing. Basements and attics may need extra vents or mechanical ventilation.
Use a dehumidifier
In basements and poorly ventilated rooms, a dehumidifier is often essential, especially during Quebec’s hot, humid summers. Choose a unit sized for the space (an undersized one will not keep up), empty the tank regularly or connect it to a drain. A hygrometer from the hardware store lets you track humidity room by room.
Fix leaks and infiltration
Plumbing leaks and seepage through the foundation are the main causes of excess moisture. Regularly inspect visible pipes and the connections under sinks and around the toilet. Any stain or discolouration on a wall or ceiling deserves a quick look. Seal foundation cracks with a suitable product.
Take care of the outside
Keep gutters clear and direct water away from the foundation. Remove dead leaves, compost and firewood piled against the house: they hold moisture and shelter several moisture bugs. Trim vegetation close to the walls to let air circulate, and if your lot slopes toward the house, regrading can cut infiltration significantly.
When to call a professional
For most moisture bugs, home remedies and fixing the humidity are enough. Call a certified technician if:
- you see cockroaches: they breed fast and need targeted treatment (see our cockroach extermination service);
- you suspect carpenter ants: structural damage is possible (see how to get rid of a carpenter ant infestation);
- the problem keeps coming back despite your efforts: the moisture source has not been found;
- mould is visible: combined with bugs, it points to a serious moisture problem;
- the bugs seem to come out of the walls: a moisture meter or thermal camera may be needed to locate the source.
A technician can inspect your whole property, spot risk areas you cannot see and recommend a treatment suited to your situation, for homes and businesses alike.
Frequently asked questions
I have a tiny bug in my bathroom: what is it?
If it is very small, white or translucent and jumps when disturbed, it is probably a springtail. If it is a bit bigger, silvery and very fast, it is a silverfish. Either way, the cause is the same: too much humidity. Improve ventilation, check the caulking and dust diatomaceous earth near the affected areas.
Why do I have bugs on my walls?
Bugs on walls, especially at night, often signal moisture inside the wall: a plumbing leak, a thermal bridge or infiltration. Silverfish and house centipedes are the most common. If dark stains appear at the same time, have the area inspected to rule out mould.
Are moisture bugs dangerous?
Most of them (silverfish, sowbugs, earwigs, springtails, house centipedes) are harmless: they do not spread disease or cause structural damage. Cockroaches, however, are a real health risk, and carpenter ants can damage structural wood. Both call for professional treatment.
Why do moisture bugs keep coming back?
Because the moisture source has not been fixed. Measure humidity with a hygrometer: if it regularly exceeds 60%, install a dehumidifier and improve ventilation. Also check caulking, pipes and the foundation for a leak or infiltration.
What humidity level should I keep to prevent bugs?
Aim for relative humidity between 30% and 50% throughout the house, as Health Canada recommends. Above 60%, conditions favour most moisture bugs, and mould.
Moisture bugs that keep coming back?
If the bugs persist despite your efforts, a technician can find the moisture source and deal with the problem at the root. We work across Greater Montreal, from Laval to Longueuil. Call us at 514-677-7526 or request a quote.
