Close the
way in.
American and oriental cockroaches come in from outside: up the drains, under doors, around pipes. Closing those gaps takes away routes and hiding places, and bait works better because they gather where you put it.
Behind sinks
and pipes
Cockroaches hide and travel through gaps behind sinks, around pipes and along skirting boards. The fix is gap and crack sealant: a paintable sealant from a cartridge with a fine nozzle.
It is in the plans for oriental cockroaches (gaps at floor level, around pipes and drains), silverfish (around baths, skirting and pipes), ants (the gap at the end of their trail) and spiders (around windows, doors and vents).
Clean and dry the surface first: sealant only holds without grease. Cut the nozzle small, since a small bead fills a small gap neatly. Let it cure as long as the cartridge says. Never seal over bait.
Under
outside doors
The gap under an outside door lets in cockroaches, ants and draughts. A brush door sweep closes it while the door still opens freely.
Measure the door width and the gap to the floor with the door closed. Cut the strip to width and screw it to the inside face, so the brush just touches the floor or the threshold. Close the door and look for light at the bottom.
It is in the plans for American cockroaches, spiders, and mice and rats.
Floor drains
American and oriental cockroaches often come up through floor drains from the sewers. A fine mesh drain cover lets water through and keeps them out.
Measure the drain first. Clear the grate and set the cover flat, with no gap at the edge. Rinse it weekly: hair and debris slow the water.
Pour water into unused drains now and then. A dry trap lets smells and insects through.
After sealing
Seal first, then bait
Seal the entry points and gaps you can reach, then bait where they still hide. Keep bait and sealant apart.
Dry it out
Fix leaks and ventilate cellars and bathrooms. Oriental cockroaches and silverfish need damp.
Outside too
Mesh under sheds and decks, fence holes fixed, animal feed stored sealed. Fewer rodents also means fewer for snakes to hunt.
Kids and pets
Any bait you add after sealing goes out of reach of children and pets. The label decides how much and where.
Renting?
Ask first.
Ask your landlord or agent before you seal, drill or screw anything on. In many places the landlord handles pests, but it depends on your country and contract.
Send a photo of the gap and of the bug, with the date. Dates and photos help if the problem comes back.