German cockroach: small, light brown, stays near warmth and humidity, reproduces indoors
Native wood cockroach: wanders in from outside in summer, does not establish indoors
Photograph the insect from above if you can – it makes identification far easier
What to do now
Keep food sealed and empty waste more frequently
Note where and at what time you saw it
Do not seal gaps yet – treatment needs to reach the harbourage
Do not deep-clean away all traces before an inspection
Why sprays make it worse
Aerosols kill the individual insects you can see and push the rest deeper into wall voids and neighbouring units. Gel bait works the other way round: it is carried back into the harbourage and reduces the population itself.
Apartment buildings in Zurich
Where kitchens and bathrooms share pipe runs, cockroaches move between flats. Treating one unit while the riser is untouched rarely holds, so the property management should be involved early.