German cockroach is active at night and hides in appliance motor cavities, structural gaps, and compressed material during the day. By the time you see cockroaches, a colony has typically been established for weeks. These are the signs that tell you an infestation is present — before you see a single live cockroach.
Frass (droppings)
Primary indicatorGerman cockroach frass: dark, cylindrical pellets 1–2mm long — similar in appearance to black pepper or coffee grounds. Found in clusters at harbourage points: motor cavity undersides, skirting board junctions, under-appliance surfaces. Fresh frass is dark; old frass lightens. Volume of frass indicates population size — heavy accumulation indicates an established colony.
Where to look
Egg cases (oothecae)
Established breeding confirmedGerman cockroach oothecae are brown, purse-shaped capsules approximately 8mm long, containing 30–40 eggs. A female carries the ootheca for most of its incubation period, depositing it close to the harbourage shortly before hatching. Finding egg cases — especially multiple cases — confirms an established, breeding colony. Empty egg cases (split along one edge) indicate the population has already hatched and is growing.
Where to look
Grease marks and smear trails
High-traffic route indicatorCockroaches leave grease and moisture deposits as they move along surfaces repeatedly. In high-traffic route locations — along the edge of a motor cavity, at a gap entry point, along a pipe run — a dark grease smear accumulates over time. This mark is the compressed result of hundreds of nightly foraging trips along the same route. Grease marks at unexpected locations (inside a riser void, along a plumbing pipe) indicate the migration route from the source population.
Where to look
Cast skins (exuviae)
Population staging indicatorCockroaches moult (shed their exoskeleton) 6–7 times during development. Cast skins are translucent, complete cockroach-shaped husks, ranging from 2mm (early instars) to 10mm (late instars). Finding multiple sizes indicates the population spans multiple developmental stages — the colony has been established for weeks or months, not days. A predominantly small-instar population indicates a recent hatch; predominantly large instars indicate a mature, established colony.
Where to look
Oily or musty odour
Large or long-established colonyA large or established German cockroach colony produces a detectable oily, musty odour from pheromone secretions and frass accumulation. The smell is strongest near the primary harbourage — inside the motor cavity, behind the refrigeration unit, in a sealed structural gap. If you detect a distinctive musty-oily smell in a kitchen or bathroom without seeing live cockroaches, it is a reliable indicator of a hidden but significant colony. The smell is often most detectable first thing in the morning before the space has been ventilated.
Where to look
Live cockroaches during the day
Severe — overcrowdingGerman cockroach is primarily nocturnal. Seeing live cockroaches during daylight hours almost always indicates overcrowding: the harbourage population is too large to contain during the night, forcing individuals into the open during the day. Daytime cockroach sightings in a kitchen are one of the clearest indicators of an established, high-density colony that requires immediate intervention. This is not an early-stage infestation.
Where to look
The combination of signs present determines severity and therefore the treatment approach required.
| Level | Indicators |
|---|---|
| Early | Occasional sighting at night only; minor frass at one location; no egg cases |
| Moderate | Regular nighttime sightings; frass at 2–4 locations; 1–2 egg cases found |
| Established | Multiple egg cases; multiple harbourage points with heavy frass; detectable odour |
| Severe | Daytime sightings; very heavy frass accumulation; odour strong; multiple rooms affected |
You can conduct a basic harbourage inspection yourself in under 15 minutes. Pull the refrigerator forward and inspect the compressor housing at the rear. Pull the dishwasher forward and look at the motor area and drain hose junction. Check the gap between the built-in oven and the adjacent cabinet at the base. Inspect the inside of under-sink cabinet lower corners. These four zones contain the core German cockroach harbourage in the majority of residential kitchen infestations.
If you find frass, egg cases, or live specimens in any of these zones, the infestation is established and a professional programme is required. Surface spray applied to visible areas will not reach these locations — see why spray reach is the fundamental limitation for harbourage-based infestations.
False positive
Cockroaches from neighbours?
Six indicators that a treated property is being repopulated from an adjacent unit rather than a surviving internal harbourage.
Case study
11 harbourage points — Somerset West
How a diagnostic inspection found what 3 previous treatments missed.
Methodology
Cockroach treatment
Harbourage-led bait programme: the approach that resolves established colonies.
A professional harbourage inspection identifies what the signs indicate and addresses every confirmed point. Early intervention before an established colony develops is significantly faster and lower-cost.
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