How to identify the cockroaches you'll actually find in Auckland

This matters more than almost any other identification question in Auckland pest control, because the answer determines whether you need a $160 perimeter treatment or a $400 baiting programme — or, quite often, nothing at all.

Only one of the cockroaches you are likely to find in an Auckland home breeds indoors and builds a population. The rest are visitors, and telling them apart is the first step in any cockroach control.

Which are the bad cockroaches in NZ?

The German cockroach is the one to worry about. It breeds indoors, spreads through buildings and is the species behind almost every genuine household infestation in Auckland. Health New Zealand names it and the American cockroach as the country's two main pest species; the American is mostly a problem in commercial buildings and drains. The Gisborne cockroach and the native black cockroach look alarming but do not infest homes.

The one that actually matters: German cockroach

Blattella germanica

• Size: 12–15 mm — small, about the length of your thumbnail
• Colour: Light tan to brown
• Key feature: Two dark parallel stripes running lengthwise on the pronotum, the shield behind the head. This is the diagnostic marking.
• Adults and nymphs: Adults have wings covering the abdomen. Nymphs are smaller, darker and wingless. Females are broader than males and often carry a brown egg case protruding from the tip of the abdomen.
• Where: Kitchens and bathrooms — behind and under fridges, dishwashers and ovens, in the void behind kickboards, in hinge recesses, around pipe penetrations
• Behaviour: Hides in tight, warm cavities during the day; you see them when a light goes on at night

This is the species that constitutes a genuine infestation. It breeds indoors, rapidly. A female carries an egg case (ootheca) containing 30 to 40 eggs until shortly before hatching — which is precisely why single treatments so often fail. The eggs are physically shielded from insecticide inside that case, so nymphs continue hatching for up to three weeks after a treatment.

Temperature explains its distribution. German cockroaches depend on heated buildings, and Rutgers University notes that their young stop developing below about 15 °C. That is why they cluster in the warmest spots in a kitchen — fridge and dishwasher motors, the oven surround — and why you do not find them breeding in gardens.

German cockroaches are also the species that spreads through apartment buildings, moving between units via risers, plumbing penetrations and shared wall cavities. If you are in an apartment, this is worth reading.

Gisborne cockroach: the one everybody panics about

The Gisborne cockroach (Drymaplaneta semivitta, te papata o Tūranga) is a large, dark, wingless cockroach that lives outdoors under bark, in woodpiles and in bark-chip gardens. It is native to Australia — Western Australia, specifically — and takes its name from Gisborne, where it was first recorded in New Zealand. It is harmless indoors: it wanders in by accident, does not usually infest food and does not breed inside.

• Size: 20–30 mm — large, and startling to find on a bedroom wall
• Colour: Dark brown to black
• Key feature: Wingless as an adult, so it has no wing covers over the abdomen, unlike the similarly sized American cockroach
• Where: Outdoors — under bark, in woodpiles, bark chips, leaf litter, garden debris. Landcare Research records it across the North Island and in Nelson and Blenheim. Indoors only by accident.
• Behaviour: Fast, usually solitary, often found in the middle of a floor or wall rather than hiding in a cavity

This is what most alarmed late-night phone calls are about, and it is almost always good news. Gisborne cockroaches do not establish indoor populations. They wander in through open doors, gaps under external doors, or on firewood, and then blunder about being conspicuous.

If you are finding one or two occasionally, the answer is usually a perimeter treatment plus tidying harbourage away from the house — moving the woodpile off the wall, clearing leaf litter from against the foundation. A full interior programme is not warranted, and we will tell you that rather than sell you one.

The drain-associated one: American cockroach

Periplaneta americana

• Size: Up to 40 mm — very large
• Colour: Reddish-brown, glossy, with a pale yellowish margin around the shield behind the head
• Key feature: Large, reddish, and capable of flight — which is memorable
• Where: Drains, sewers, grease traps, warm commercial voids, boiler rooms

In Auckland this turns up mainly in commercial kitchens, older buildings and around compromised drainage rather than in ordinary homes. Where we do find it in a residential property, the underlying issue is frequently a drainage fault worth investigating.

Its close relative the Australian cockroach (Periplaneta australasiae) is similar but with distinct pale yellow streaks on the leading edge of each wing.

The native one: black cockroach

Platyzosteria novaeseelandiae

• Size: About 20 mm
• Colour: Glossy black, uniformly, with no stripes or markings
• Key feature: Flightless, with reduced wings; distinctly shiny
• Where: Native bush, gardens, under logs and stones

New Zealand has a number of native cockroach species and they are not domestic pests. They do not breed indoors, do not spread disease in the home and need no treatment. If this is what you are finding — most likely on a bush-edge property in Birkenhead, Henderson or similar — the correct response is to put it back outside.

Manaaki Whenua Landcare Research runs a public identification service if you want an independent opinion on a specimen.

Quick comparison

How can you tell which type of cockroach you have?

Size, numbers and location tell you most of what you need, and you do not need to catch one. A small light-brown cockroach in the kitchen, seen more than once, is a German cockroach until proven otherwise. A single large dark one on a wall or floor is almost always a Gisborne cockroach that came in from outside. These three questions get you most of the way:

1. How big? Under 15 mm points to German. Over 20 mm points to Gisborne, American or native.
2. How many? Multiple sightings, especially in the kitchen, point to German. One or two occasional large ones point to a wanderer.
3. Where? Kitchen and around appliances points to German. Middle of a bedroom floor, bathroom wall or laundry points to a wanderer that came in from outside.

If you can photograph it, do. Email a clear photo and we will identify it before anyone visits — which frequently saves a call-out entirely.

Why identification changes the treatment so much

German cockroaches need targeted gel baiting placed directly into harbourage, usually combined with an insect growth regulator, and a mandatory follow-up at 10 to 21 days to deal with the generation that hatches from protected egg cases. Spraying surfaces achieves very little — it does not reach into the cavities where they actually live, and it can cause them to disperse further through the building.

Gisborne cockroaches need an external perimeter treatment and, more importantly, the removal of harbourage against the building. That is a fundamentally cheaper and simpler job.

Treating the second as though it were the first wastes several hundred dollars. Treating the first as though it were the second guarantees the problem returns. This is the whole argument for identifying before treating — and it is why our cockroach control jobs always start with working out what you actually have.

Frequently asked questions