The three reliable diagnostics
- Two parallel dark stripes on the pronotum (the shield directly behind the head) — the single most reliable identifier. Present in adults and larger nymphs. No other common BC cockroach species has this marking combination.
- Size 12–15 mm for adults — distinctly smaller than American cockroaches (35–40 mm), roughly comparable to brown-banded cockroaches at maturity but differentiated by stripe pattern and habitat preference.
- Light brown body color — neither the deep reddish-brown of American cockroaches nor the very dark colour of Oriental cockroaches. Adults are pale brown; nymphs grade from near-black (early instars) to light brown (later instars).
| Feature | German | American | Oriental | Brown-banded |
|---|---|---|---|---|
| Size (adult) | 12–15 mm | 35–40 mm | 25–30 mm | 10–14 mm |
| Colour | Light brown | Reddish-brown | Dark brown/black | Light brown |
| Pronotum markings | 2 dark parallel stripes | Pale figure-8 pattern | No distinctive markings | No distinctive markings |
| Wings | Present, rarely flies | Present, occasional short flights | Vestigial in female, short in male | Present |
| Preferred habitat | Warm/humid kitchens, high-rise voids | Sewers, boiler rooms, large buildings | Cool/damp, drains, sewer lines | Warm/dry, electronics, upper cabinets |
| Ootheca size | 7 mm, 30–40 eggs | 8 mm, 14–16 eggs | 8–10 mm, 16–18 eggs | 5 mm, 14–18 eggs |
| Metro Van frequency | Very common (dominant) | Occasional (commercial) | Uncommon | Rare |
Identifying nymphs — the stage most people miss
German cockroach nymphs are frequently overlooked or misidentified because they look markedly different from adults. First-instar nymphs are approximately 1.5–2 mm long, nearly black, and wingless. At this stage the parallel stripe pattern is already present if you look closely, but the small size causes most people to mistake them for small beetles or other insects. As nymphs progress through six instar stages over 60–100 days, they progressively lighten in colour — early instars are dark, mid-stage nymphs show the brown beginning to appear, and late instars are close to adult colour. Wingpads (small undeveloped wing cases) appear in later instars but do not function until the final adult molt. If you see what looks like a very small cockroach without wings, that is almost certainly a late-instar German cockroach nymph. Nymph sightings are significant: they indicate active reproduction in the unit, not just adult migration. A population with visible nymphs requires more thorough treatment than one with only adult sightings.
Oothecae (egg cases) — the survival structure
German cockroach oothecae are 7 mm long, brown, rectangular capsule-shaped structures with a finely ridged surface. Each ootheca contains 30–40 eggs arranged in two rows. The female carries the ootheca attached to her abdomen for most of the egg development period — approximately 28 days under warm conditions. She deposits the case in a protected harborage approximately 24 hours before hatching. This carrying behaviour is diagnostically useful: if you see a female cockroach with a brown capsule protruding from her rear, that confirms an actively reproducing German cockroach colony. The ootheca's hard case provides substantial resistance to contact insecticides — this is one of the key reasons surface spray protocols fail to achieve lasting control. Gel-bait plus IGR protocols address this by either reaching the reproducing female via horizontal bait transfer, or by disrupting development via IGR before nymphs can mature to reproductive adults.
How to confirm an active vs. historic infestation
If you've moved into a unit with visible cockroach evidence, the first question is whether the infestation is active or historic (the previous tenant dealt with it, remaining evidence is residual). Deploy three to four sticky monitor traps at likely activity sites — behind the refrigerator, under the stove, inside cabinets near plumbing. Leave them for 48–72 hours. Live captures confirm active infestation; no captures with 72-hour exposure and no new droppings in clean areas strongly suggests historic evidence. Even one live capture in 48 hours warrants a professional assessment in a multi-unit building, because the population may be in adjacent units with only occasional visitors entering yours. See [cockroach signs in your Metro Vancouver apartment](/guide/cockroach-signs-in-apartment) for the full evidence guide.
When the ID changes the protocol
American cockroach sightings (large reddish-brown, 35–40 mm) in a Metro Vancouver residential building usually indicate a sewer-connected ingress problem — these cockroaches enter from building drains, not from adjacent units. The control approach is different: drain covers, sewer-line investigation, perimeter exclusion, and a trap-monitoring program rather than the gel-bait + IGR suite that dominates German cockroach work. Oriental cockroaches in a basement or ground-floor unit indicate similar sewer/drainage ingress. Brown-banded cockroaches — if confirmed — require treatment in different locations than German cockroaches (upper cabinets, electronics rather than kitchen low-level) and respond to gel bait but in different placement patterns. Accurate identification before treatment is one of the reasons the BC IPM Act mandates an inspection component for all commercial pest control work.