German cockroach (Blattella germanica) in New Zealand

The German cockroach is sometimes jokingly called the “five star cockroach” due to its close association with restaurants and hotels.

Despite its name, it is not native to Germany. Recent evidence suggests it emerged in south east Asia.

Invasive

Found worldwide and throughout New Zealand.

German cockroaches are only found around humans and in areas of human activity – they are truly domestic cockroaches. Although they are found worldwide, they can only survive in heated buildings in colder climates.

They typically harbourage in cracks and crevices in kitchens and food preparation areas, but also bathrooms and laundries – they need access to water and food. In kitchens they will hide behind and under cupboards and crevices, in cupboard hinges, in dishwashers (including control panels, in and under microwaves and toasters, in extraction fans and more.

As they travel only small distances, their harbourage will be within 1-2 m of a food source.

German cockroaches live in aggregations – cockroaches of all ages (young nymphs to adults). Whereas the cockroaches don’t activity co-operate as a community, the young cockroach nymphs, which tend not to leave the harbourage, benefit from this arrangement as they feed on the droppings and vomit of older cockroaches.

Due to their small size they are able to live in large numbers in the smallest of spaces.

Typically, field populations consist of 80% nymphs and 20% adults.

Adults:

Colour: Tan to dark brown, with two dark stripes running the length of the pronotum (shield behind the head)

Size: Up to 15 mm

Males: Thin and slender

Females: Short and stout (wider than tegmina – leathery outer wings)

Nymphs:

Colour: Dark brown to black with distinct dark parallel lines running the length of the pronotum.

Size: From 3 mm

Eggs: 30-40 eggs per ootheca (egg case). Ootheca carried until just before hatching – sometimes hatching before the ootheca is deposited.

Number of nymphal stages/moults to adult: Varies, but most frequently 6.

Length of life-cycle (Egg to adult): 100 days

Life span of adult: Up to 6 months

Cockroaches will eat everything! They are scavengers that will eat any organic matter – A wide range of food and non-food items. They will even eat their dead nest mates!

• German cockroaches only travel 1-2 m from their harbourage to feed and young nymphs do not leave their harbourage at all
• The female carries her ootheca (egg case) until just before hatching, ensuring a high level of survival and that the nymphs are placed in a suitable harbourage
• The droppings from German cockroaches are small brown spots, which may be seen in the corners of cupboards and on door hinges
• It is sometimes confused with the brown banded cockroach. However, the brown banded cockroach lacks the vertical dark bands on the pronotum (shield behind head) and instead has two diffuse dark horizontal bands across the thorax.
• It is very similar to the closely related Asian cockroach. However, the Asian cockroach is attracted to light and flies like a moth, unlike the German cockroach

Cockroaches are viewed as “dirty” insects, mainly due to their association with sewers and human waste. Indeed, they have been shown to carry a wide range of different diseases, in particular gastro bacteria such as Salmonella and E. coli, as well as a number of parasitic worms. When they move across food preparation surfaces and feed on any exposed food, there is always the potential to transfer these diseases to humans.

The spent skins and droppings of the German cockroach contain allergens that can trigger allergic reactions and asthma attacks. German cockroach infestations in inner city tower blocks in the US are considered one of the major causes of childhood asthma.

Good hygiene is key to preventing a cockroach infestation:

• Keep food preparation areas clean – clean up food spills and clear away dishes after meals
• Make sure the dishwasher is run regularly
• Regularly clean cooker, grill, extraction fan, dishwasher and refrigerator (especially underneath)
• Don’t leave unfinished pet food out overnight
• Fix any leaks and areas of moisture
• Fill any cracks and crevices, that would allow cockroaches easy access from the outside
• Ensure rubbish is put into sealed containers