Silverfish, booklice or a young cockroach?
| Silverfish | Booklice | Cockroach | |
|---|---|---|---|
| Size | Up to about 15 mm when mature | Tiny, 1 to 2 mm | German adults are 12 to 15 mm; young ones smaller |
| Looks like | Silvery grey teardrop with three thread-like tails | Pale, slightly see-through brown speck, no wings | Flat, brown, fast, with long antennae |
| Moves | Freezes, runs for cover or hops | Slow, in small groups | Runs for the dark |
| Eats | Paper, glue, cotton | Microscopic mould on paper and glue | Almost anything |
Silverfish
They favour humid rooms and they're mostly out at night, so you tend to meet one when you turn the light on or lift a towel. Indoors they may eat starchy things such as wallpaper glue, book bindings and photographs. A few around the bath isn't a crisis. Our silverfish page has more.
Booklice
These look like moving dust on a damp windowsill or on old paper. They feed on microscopic moulds, so a lot of them is really a message about moisture. Dry the room and the numbers usually drop away.
Cockroaches
Health NZ says cockroaches thrive in warm and damp conditions, and that they prefer dark places. Behind the washing machine, around the hot water cylinder and in the gap behind the vanity are the obvious spots. One seen once may be a visitor. Regular sightings call for cockroach control.
White-tails
White-tailed spiders are often found in bathrooms and laundries, and the washing pile suits them. Health NZ says a bite causes pain, swelling and itching that go away with no long-lasting effects, and that they don't cause skin damage or ulcers. Clean a bite with antiseptic or warm soapy water, and read the white-tail page if you're worried. Give towels and clothes on the floor a shake before use.
How they get in
The gaps around the pipes under the basin and behind the washing machine are the usual road from the wall cavity or subfloor. Check where the waste pipe goes through the floor, too. Many of these animals are already living in the house, and they've simply moved to the wettest room.
What to check
- Does the fan actually pull air out, and do you run it long enough?
- Is there mould on the ceiling, or paint lifting near the shower?
- Any slow drip under the basin or behind the washing machine?
- Are there gaps around pipes where they enter the wall or floor?
- Are towels or laundry left on the floor for days?
- Is there cardboard or old paper stored in the laundry?
What helps, and who does it
You can
- Run the fan and open a window after showers.
- Fix drips and dry out cupboards under basins.
- Fill pipe gaps with a suitable sealant.
- Move cardboard and paper out of damp rooms.
- Vacuum along the skirtings.
Leave to a pest business
- Cockroaches that keep coming back.
- A general treatment if numbers of spiders or silverfish stay high after the room dries out.
- A plumber or builder for leaks inside walls.
Is it worth a call?
Often not. If it's silverfish or booklice, give the room a month of dry air and sealed gaps before you spend anything. One white-tail doesn't need a technician either. Cockroaches are the exception: if you're seeing them most weeks, tap Cockroaches and let a pest business find where they're breeding.
Want someone to look at it?
Tell us what you've seen and your postcode, and a local pest business that handles exactly that calls you to talk it through.
