Identifying cockroaches

German cockroach

The German cockroach is the one most homes have. It is small, light brown or tan, and the two dark stripes behind its head are the giveaway. It breeds fastest of the common species, on a six to eight week cycle, and lives in kitchens, bathrooms and behind appliances.

It likes warmth and moisture. Look behind the fridge and cooker, under the sink and around dishwasher pipes. Small ones seen at night are often young and mean breeding is under way.

Because it multiplies so quickly, a German cockroach is the species where waiting costs most. See cockroach control for what treatment involves.

Oriental cockroach

The oriental cockroach is larger, 20 to 25 mm, and dark brown to black with a glossy body. It prefers cooler, damp places such as basements, drains and utility rooms, and often arrives from outside or from a drain.

It is slower to multiply than the German cockroach, taking six to twelve months per generation. A single large dark cockroach in a ground-floor kitchen at night is often this species. If you find several, check drains, gaps around pipes and any damp, cool areas near the building.

Signs of an infestation

You may see the signs before the insects. Look for:

• droppings like coarse ground black pepper
• egg cases about 8 mm long
• shed skins
• a musty smell
• dark smears along walls and skirting

Seeing cockroaches in daylight usually points to a large population, because they prefer the dark. Check at night with a torch, and look inside cupboards and behind appliances.

Lookalikes

Several things get mistaken for cockroaches:

• Beetles have shorter antennae and a rounder, harder body. Cockroaches have long antennae and flat bodies.
• Silverfish are silvery and tapering, and move with a wriggle.
• Mouse droppings are 3 to 6 mm and rice-shaped, so they differ from the finer, pepper-like cockroach droppings. See mouse control if you suspect mice.

If you are unsure, take a clear photo and send it to a technician. Naming the species decides what treatment will work.

Where to look

Cockroaches hide in warm, dark, damp cracks close to food and water. Check at night with a torch, since they are most active in the dark. Start with the kitchen: behind and under the fridge, cooker and dishwasher, inside cupboard hinges and under the sink. Then check the bathroom, around waste pipes, and any utility room or cellar.

Look for cockroaches themselves, then for droppings, shed skins and egg cases. The more signs you find, in more places, the bigger the problem. Photograph what you find so a technician can tell you the species before a visit.

Is it a sign of a dirty home?

Not necessarily. Cockroaches spread through shared pipes, walls and voids, so a clean flat can have them if the building does. Poor hygiene helps them thrive, but it is rarely the only cause.

Once you have identified them, the next step depends on the species and scale. Our DIY guide covers a small problem, and the cost guide covers hiring help.