Cockroaches

What does a cockroach nest look like?

Cockroaches do not build nests, they gather in warm cracks. What a German cockroach harbourage looks like, where it hides in a kitchen or wall, and what to do next.

The short answer

Cockroaches do not build a nest. What people find is a harbourage, a tight, warm, dark gap where German cockroaches gather in numbers, marked by droppings like ground pepper, dark smears, pale shed skins, egg cases and small dark nymphs. In an Auckland kitchen it is usually behind the fridge or the dishwasher kickboard, or inside an appliance, and finding it is the first step in treating German cockroaches.

At a glance

Cockroach signs by species

Cockroach signs by species
Sign	German	American	Gisborne
Adult size and look	13–16 mm, tan, two dark bars behind the head	35–40 mm, reddish brown	20–30 mm, black, pale side stripes
Droppings	Tiny, like ground pepper, with dark smears at crack edges	Larger, cylindrical pellets	Rarely noticed indoors
Egg case	About 6 mm, light brown, carried by the female until a day or two before hatching	About 9–10 mm, dark, glued to a hidden surface	Rarely seen indoors
Where you find them	Fridge motor, dishwasher, oven sides, sink cabinet, hinges	Drains, floor wastes, subfloors, grease traps	Bathrooms and laundries at night
Shed skins seen?	Often, around the harbourage	Sometimes, near drains	Rarely
Breeds indoors?	Yes, rapidly	Yes, in wet voids	Not usually

Do cockroaches make nests?

Not in the way ants, wasps or birds do. Cockroaches build nothing. They gather where conditions suit them, drawn together by an aggregation pheromone in their own droppings, and they prefer gaps tight enough that a surface touches them above and below. Once a few have settled in a crack, the droppings they leave pull in more, which is why one spot becomes heavily used while the cupboard next to it stays clean.

So when people say nest, what they have found is that harbourage: a crack, hinge gap or appliance cavity with cockroaches of every age packed into it, plus everything they leave behind.

What a German cockroach harbourage looks like up close

Look for dark specks the size of cracked pepper, often in a line along the edge of a gap, and brown smears where the specks have been rubbed or wetted. Pale, papery shed skins lie around the opening, because nymphs moult several times as they grow. Egg cases are light brown, purse shaped and about 6 millimetres long, and you may see empty ones split along the top. Then the cockroaches themselves: adults with two dark bars behind the head, and small, wingless, darker nymphs.

There are no photographs on this site, so the table above sets the German, American and Gisborne signs side by side in measurements instead.

Where to look in a kitchen, room by room

Search after dark with a torch, about half an hour after the lights go off, because German cockroaches are nocturnal and the harbourage is easiest to find while they are out. Start with heat and water. Pull the fridge forward and look at the compressor and the warm plate behind it, then take off the dishwasher kickboard, check the sides of the oven and the cabinet under the sink, and lift the kettle, toaster and microwave to look at their bases.

Then the small gaps: cabinet hinges, the join where the benchtop meets the wall, and the back corners of drawers. In a bathroom, look behind the vanity and around the pipes. Everything here can be checked without tools except the kickboard and, sometimes, the fridge.

Cockroaches in a wall cavity

A cockroach nest in a wall shows itself at the openings: droppings and smears at power points, at the holes where pipes come through, and along skirting gaps, with cockroaches appearing from the same points at night. German cockroaches use those cavities to move between rooms and, in apartments, between units.

American cockroaches are the other wall and floor species, usually coming up from drains through a floor waste whose water seal has dried out. Do not spray into a wall cavity. It pushes German cockroaches further in and spreads them, and in an apartment block it is a building problem that the body corporate has to deal with as one job.

Small cockroaches in the kitchen at night

Small cockroaches in a kitchen at night are almost always German cockroach nymphs, and nymphs mean breeding is happening in that kitchen. They will not go away by themselves, and a fly spray will only scatter them. Find the harbourage using the list above, and treat it with gel bait placed into the gap rather than with a spray across the surface.

Meanwhile, cut off water: dry the sink at night, fix any drip under it, and do not leave pet water bowls out overnight in the kitchen.

Gisborne cockroaches: the big ones with no indoor nest

Gisborne cockroaches look alarming but are not a problem in the way German cockroaches are. They are an Australian species that lives outdoors around timber, bark and garden mulch, they wander in on warm nights looking for moisture, and they do not usually infest a house or its food. One in the shower is a visitor. A door seal, a bead of sealant around a pipe and moving bark chips back from the walls are the answer.

Questions

Cockroach nest questions

What attracts cockroaches into a house?

Warmth, water and shelter more than mess. German cockroaches settle where an appliance motor keeps a cavity warm and a drip or condensation keeps it damp, and food crumbs are a bonus. Many arrive already living in a second-hand appliance or a cardboard box, so a spotless kitchen can still end up with them.

Do cockroaches nest in fridges?

Around them, yes. The motor compartment at the back and the insulation and gaps around it are warm, dark and rarely cleaned, which makes them one of the most common German cockroach harbourages we find. The inside of a working fridge is too cold for them to live in, so cockroaches seen inside it have come from the cavity behind.

Where do cockroaches lay their eggs?

German cockroaches do not lay eggs loose. The female carries a single egg case, with 30 to 40 eggs inside, on the end of her body until a day or two before it hatches, then drops it in the harbourage, so the eggs end up in the same warm cracks as the adults. American cockroaches carry theirs for a few days and then glue it to a hidden surface near their shelter.

Is there anything that kills cockroach eggs instantly?

Not in practice. The egg case is tough and shields the eggs from sprays, which is why eggs laid before a treatment still hatch two or three weeks later. The answer is timing rather than strength: bait the harbourage, then treat again inside the hatch window so the nymphs are caught as they emerge.

Does one cockroach mean there is a nest?

It depends on the species. A single large Gisborne cockroach has almost certainly walked in from the garden. A single small German cockroach, especially one seen in daylight, usually means a harbourage nearby with many more in it, because they hide by day and only show themselves when crowded or disturbed.

Are cockroach droppings harmful?

They can be for people with asthma or allergies. Cockroach droppings, saliva and shed skins carry allergens that can trigger asthma, especially in children. Clean up with a vacuum fitted with a HEPA filter rather than a broom, and if a member of the household has asthma, have someone else do it. See your doctor if asthma gets worse while cockroaches are around.

If you need someone

Treating the cockroaches you have found

Cockroaches

Cockroach Control

The species decides the treatment.

Read about it

More advice

Other things worth knowing

Identification