Signs of a Cockroach Infestation: How to Know if You Have Cockroaches

Cockroaches are nocturnal and secretive. For every cockroach you see, there are likely dozens — sometimes hundreds — you don’t. By the time most people notice they have cockroaches, the infestation is already well established.

Knowing the signs means you can act before the problem grows.

Species in London

Two cockroach species are commonly found in London properties:

German cockroach (Blattella germanica): The most common indoor cockroach species. 12–15mm long, light brown with two dark stripes behind the head. Prefers warm, humid environments — kitchens, bathrooms, behind appliances. Does not fly, despite having wings. Produces the largest populations.

Oriental cockroach (Blatta orientalis): Larger (20–25mm), darker (almost black), and slower moving. More commonly found in cooler, damper areas — basements, drains, underfloor spaces. Less common than German cockroaches but associated with older housing.

Sign 1: Live Cockroaches

Seeing a cockroach during the day is a significant warning sign. Cockroaches are photophobic — they avoid light and are primarily active at night. A cockroach visible during daylight hours suggests the population has grown large enough that competition for harbourage is driving individuals into the open.

If you switch on a kitchen light at night and see movement — cockroaches disappearing into gaps around appliances or under units — that’s strong evidence of an established population.

Sign 2: Droppings

German cockroach droppings look like dark pepper or coffee granules — 1–2mm, black or dark brown. They’re typically found in concentrated areas close to harbourage: behind and underneath appliances, in drawer runners, along skirting boards, in the corners of cupboards.

Oriental cockroach droppings are larger — cylindrical, 3–5mm — and tend to appear in damper areas.

The quantity of droppings gives a rough sense of population size. A fine dusting suggests early-stage; dense accumulations across a wide area suggest a serious infestation.

Sign 3: Egg Cases (Oothecae)

Cockroaches produce distinctive egg cases called oothecae. German cockroach oothecae are 8–10mm long, brown, and capsule-shaped. Each contains 30–40 eggs. After hatching, the case remains and is often found in harbourage areas.

Finding egg cases is confirmation of breeding activity — meaning the population is self-sustaining and will continue to grow without intervention.

Sign 4: Shed Skins

Cockroaches moult as they grow, passing through several nymph stages before reaching adulthood. Shed skins — translucent, cockroach-shaped husks — accumulate in harbourage areas. Multiple skins indicate a substantial, active population.

Sign 5: Smell

A large cockroach infestation produces a distinctive musty, oily odour caused by the insects’ pheromones and aggregation chemicals. If your kitchen has an unpleasant smell that you can’t attribute to food waste or drains, cockroaches are worth investigating.

Sign 6: Damage to Food and Packaging

Cockroaches are omnivores that will eat almost anything — food, cardboard packaging, grease, soap, paper, adhesives. Irregularly chewed food packaging or smear marks on food containers can indicate cockroach activity.

Where to Look

If you suspect cockroaches, inspect with a torch in the following locations:

• Behind and underneath the fridge and dishwasher
• The motor compartment at the back of the fridge (warm and dark)
• Beneath and behind the cooker
• Inside cupboards, particularly at the back and in corners
• Drawer runners
• Behind loose skirting boards or tiles
• Around pipes where they enter or exit the building
• In drain traps and beneath sinks

What to Do if You Find Signs

Do not delay. German cockroaches in particular breed rapidly — a single female and her offspring can produce 30,000 cockroaches in a year under ideal conditions. Early-stage infestations are contained to one area and require fewer visits. Established infestations spread through wall voids and can affect multiple rooms.

Don’t use shop-bought foggers. They disperse insects rather than kill them, spreading the infestation and making professional treatment harder.

Contact a professional immediately. Professional treatment uses gel baits, insecticide sprays, and dust formulations targeted to cockroach behaviour — placed in harbourage areas the insects actually use, not sprayed across open surfaces.

We carry out cockroach control across all 33 London boroughs. Treatment typically requires 2–3 visits. Request a quote online for same-day advice and attendance.