Blattella germanica (Linnaeus, 1767)

German cockroach

A small, fast-breeding indoor cockroach, the most common cockroach found in Ontario homes and restaurants.

Order: Blattodea
Family: Ectobiidae
Group: Cockroaches
Ontario status: Established, indoor obligate; cannot overwinter outdoors

Why it matters

Can carry germs such as Salmonella on its body, and is a major indoor allergen, cockroach allergens are an established trigger for asthma, especially in children.

Origin

Despite the name, not from Germany, likely Southeast Asia in origin, now worldwide via human trade and shipping.

Behavior

Nocturnal; hides by day in tight cracks and comes out at night to feed. Gathers in groups using scent signals, where you see one, many are usually hidden nearby.

Living conditions

Strictly indoor in Ontario; cannot survive winter outdoors. Needs warmth (25-33 °C), moisture, and tight cracks near food, behind fridges, inside wall voids, under sinks.

Signs of presence

Small dark droppings like ground pepper near food areas
Musty, oily odor in heavy infestations
Oval brown egg cases (oothecae) - carried by the female until ~1 day before hatching, so intact cases are rarely found
Live insects scattering when lights turn on at night

Weaknesses

Cannot overwinter outdoors in Ontario, indoor-only
Nymphs dry out fast without humidity
Needs accessible food, water and harborage, remove all three and populations collapse

Myths and facts

Myth Seeing one cockroach means there is only one.
Reality German cockroaches aggregate; a visible one usually means many hidden nearby.
Myth They bite people.
Reality They do not bite; the health concern is contamination and allergens, not bites.

Research notes

Morphology

Adults 13-16 mm, pale brown with two dark parallel stripes on the pronotum. Wings fully cover the abdomen in both sexes; rarely flies. Nymphs wingless, dark brown to black with a pale longitudinal band.

Diagnostics

Confirm by pronotal stripes + adult size 13-16 mm + female carrying ootheca. Nymphs: dark with pale band, no wing pads in early instars.

Easily confused with

Asian cockroach, Blattella asahinai Nearly identical; Asian cockroach is a strong flier attracted to light outdoors, German cockroach is indoor and rarely flies.
Brown-banded cockroach, Supella longipalpa Brown-banded shows two pale transverse bands across the back; German shows two dark stripes on the pronotum.

Life cycle

Adult: Lifespan ~100-200 days; females produce 4-8 oothecae in a lifetime.
Egg: Ootheca containing 30-40 eggs, carried by the female until ~24 hours before hatching.
Egg to adult: 50-60 days at 30 °C; markedly slower below 25 °C
Generations per year: 3-4+ indoors (continuous breeding)
Nymph or larva: 6-7 nymphal instars; wingless; dark with pale band.

Development

Incomplete metamorphosis: egg → nymph → adult.

Reproduction

30-40 eggs per ootheca, 4-8 oothecae per female, a single female can seed hundreds of descendants within months.

Distribution

Global: Cosmopolitan, worldwide in human buildings
Native range: Likely Southeast Asia
Ontario: Established provincewide indoors; cannot overwinter outdoors

Ecology

Thigmotactic, prefers tight cracks and crevices. Aggregates via aggregation pheromone deposited in feces. Foraging range small (a few metres from harborage); omnivorous scavenger.

Resistance

Widespread pyrethroid resistance via kdr target-site mutations; metabolic resistance (elevated cytochrome P450s, esterases) documented in North American populations.

IPM implications

Monitoring should target tight harborages near warmth, moisture and food (sticky traps placed in cracks and voids, not open floors). Reproduction is continuous and rapid, so monitoring intervals must be short and any visible count assumed to underrepresent the true population. Documented resistance means susceptibility cannot be assumed, resistance management (mode-of-action rotation) applies.

Chemical ecology

Aggregation pheromone in feces drives clustering at harborages; cuticular hydrocarbons mediate kin and nestmate recognition.

Genetics and DNA

Genome sequenced 2018 (~2.0 Gb), one of the largest insect genomes; expanded chemoreception and detoxification gene families (Harrison et al., Nature Ecology & Evolution).

Taxonomy

Order Blattodea, family Ectobiidae (formerly Blattellidae). Described by Linnaeus, 1767.

Open questions

Precise contribution of the Blattabacterium endosymbiont to insecticide tolerance; population genomics of Ontario infestations.

References

Harrison et al. 2018, Nature Ecology & Evolution (genome)
Ebeling, W. Urban Entomology, UC Riverside
Mallis Handbook of Pest Control