GERMAN COCKROACHES – The Public Health Pest in Your Home

Written by Anthony O’Neill – Licensed Pest Management Professional

German cockroaches are filthy pests that carry harmful bacteria which they leave on our food, countertops and anywhere else they crawl across. And if that’s not bad enough, they are prolific breeders and produce hundreds of nymphs in just one year!  Here is everything you need to know about this public health pest. 

What is a German Cockroach?

The German roach (Blattella germanica) is a public health pest and is the world’s most common species of cockroach to infest homes, workplaces, restaurants, and multi-family housing.^[1] 

This roach is synanthropic (associated with humans) so it lives alongside us in our homes and pretty much anywhere humans are.  It thrives in warm, moist environments like the kitchen, and spends around 75% of the time hidden away in cracks and crevices close to food and water sources. 

German cockroaches are omnivorous and eat a variety of things, including food, paper, hair, glue, soap, and other dead roaches.  This pest is not only filthy, but it can also cause allergies and asthma.

What Do German Cockroaches Look Like?

German roaches belong to the group known as small cockroaches and are mainly identified by the two dark parallel stripes on the pronotum.  The following are their overall identifying features:

Adult German Roaches

• They are about ½” – ⅝” (12.7 – 16 mm) long when fully grown.
• They have flattened, oval-shaped bodies with six spiny long legs and two long antennae
• Adults are light brown to tan in color
• They have two dark parallel stripes on their pronotum (the shield-like area behind their head), as does the Asian cockroach so they look almost identical. 
• Adult males have narrower bodies than the females
• Female adult German roaches have a rounded, wider abdomen so they can carry the protruding egg case.
• Females are slightly darker than the males
• They have fully developed wings, but do not fly

German Cockroach Nymphs

• Nymphs are about ⅛” (3 mm) long when they emerge from the egg case or ootheca.
• Baby roaches are white and their bodies are soft when born and also after each molt, but turn dark brown to black in color once their exoskeleton hardens.
• They have dark-colored stripes that extend down their back.
• Nymphs do not have wings.

German Cockroach Life Cycle

In comparison with other cockroach species, the German roach has a much higher reproductive rate and it takes considerably less time for them to grow from nymph to adult, especially when compared to the American cockroach for example. 

However, as with all cockroach species, this roach also undergoes the same three stages of incomplete metamorphosis, which are: egg, nymph, and adult.

German Cockroach Eggs

The light brown purse-shaped egg sac is 1/4 – 3/8″ (6.35 – 9.5 mm) long and 5/64″ wide (2 mm) and contains between 30 – 48 eggs.

The female carries the egg case or sac (ootheca) partially inside her abdomen for around 28 days and drops it somewhere safe and hidden away from predators a day or two before it hatches. This makes it difficult to spot them, especially in the early stages of an infestation.

Additionally, carrying the ootheca helps to also prevent dehydration since the female supplies the egg case with moisture. Having the ootheca protected, together with the increased number of eggs per egg case, is the reason why the German roach has the highest reproductive capacity out of all pest cockroach species.

However, if the female drops the egg case before the nymphs are ready to hatch, they will not emerge and will die of dehydration.

Baby German Roaches

What do baby cockroaches look like?  A baby German roach looks like the adults except for their size which is obviously smaller. The other difference is the lack of wings.

I took the photo of roaches below when treating a heavily infested property and you can see the adults and the nymphs, which are of various sizes hiding in a cabinet door hinge.

When the nymphs hatch from the ootheca they have soft, white bodies and are tiny in size at about 1/8″ (3 mm) as mentioned above.

After a few hours, their bodies harden and change to a dark brown/black color. They have two dark parallel stripes on their pronotum that also extend down the back.

These juvenile roaches are hungry and soon go looking for food. At room temperature and with enough food and moisture, baby roaches develop and reach adulthood in around 54 – 100 days under the right conditions.

During that development time, they go through 5 to 7 nymphal stages (instars) where they shed their exoskeleton every time so that they can grow. When a cockroach nymph molts, it seeks out a protected area where it can hide from predators.

As well as looking like a white roach when they are born, they are also white after each molt (aka ecdysis) but become darker over a few hours once pigmentation is restored.

During molting, nymphs must take in large amounts of air to inflate themselves so they can split and shed their outer cuticle.

Juvenile roaches become adults when the final molting stage takes place. The newly emerged adults have wings and can now mate and will reproduce at an alarming rate.

Adult Blatella Germanica

German roaches have the highest rate of reproductivity of all the common roach types, and they certainly produce a lot of offspring.

As said above, after mating the adult female produces an egg capsule containing 30-48 eggs. The female roach can procreate throughout the year in a humid environment with an average temperature of 80°F (27°C). At this temperature, there will be a new egg capsule every 6 weeks from this same female, resulting in 6-8 egg cases annually.

It has been reported that a single female and her offspring can produce over 30,000 individuals in a year.^[2] This rate of reproduction explains why an infestation can grow so quickly as it comprises around 75% nymphs and only 25% adults.^[3]

How Long Do German Roaches Live?

The average life span of both adult male and female german roaches is between 100 – 200 days (males typically around 130 days and females around 150 days)^[4]. It doesn’t sound like a long time but it is enough for them to create a rapidly growing infestation.

German Cockroach Infestation Signs

These pests thrive in areas where there is heat, humidity, and moisture.

In the early stages of an infestation, German roaches will usually only be found in the kitchen and bathrooms because these provide access to water and moisture through leaky taps and pipes, and warmth from heat-producing appliances, such as a refrigerator.

As the cockroach population grows or if sanitation is poor, they will spread out to other areas of the home, especially if these other areas have what attracts roaches the most – food, water, and shelter. 

Here are some telltale signs of a roach infestation to look out for:

Cockroach Droppings

As these small roaches look for food and scurry across your kitchen countertops and inside your cabinets and drawers at night they leave behind their droppings (frass).

German roach droppings are easily identified because they look like coffee grounds or ground specks of black pepper. In fact, roach poop looks similar to bed bug feces. At first, most people are unaware it’s roach feces because it’s unlikely you’ll see these pests during the day unless, of course, you have a large infestation.

The following image I took shows where they have congregated as there are plenty of droppings and fecal stains.

Smear Marks/Fecal Staining

Another sign to look for is any dark staining or smear marks in corners of the walls, in and around cracks in walls, under the refrigerator, on the tops of doors, and in other areas where they cluster.

These areas are marked with an aggregation pheromone found in their droppings which attracts other roaches to cluster in these areas.

Egg Cases

As you know, German roach egg cases are tiny but you can find these light brown, oblong-shaped casings if you look carefully. Places to check are anywhere there is a crack or crevice, such as in the walls, in drawers, and door hinges and trims.

The nymphs inside the case will split it open and emerge leaving the empty egg casing in place.

Seeing Roaches In The Daytime

If you see a roach scurrying around your kitchen or bathroom during the day, then this is a good indication that the population levels have grown significantly. These pests usually only come out during the day if their hiding areas have become overcrowded and they need to find somewhere to shelter.

As their population grows, it becomes harder for them to easily access food and moisture so they have to come out and search for them in other areas.

Other indications of a heavy infestation also include finding dead roaches and shed skins left behind during a molt.

Can You Smell German Cockroaches?

Can you smell a cockroach infestation? Some people notice an unpleasant odor when the infestation is fairly big, but others don’t detect a cockroach smell at all.

The odors are produced by several things including decomposing dead cockroaches. When a roach dies, its body produces oleic acid which is a foul-smelling odor that other cockroaches stay away from.

Other roach smells are caused by pheromones produced in the fecal droppings. These secretions are used as forms of communication to aggregate other roaches to an area or to attract a mate.

The best way to probably describe the smell is as pungent and offensive that has a heavy, sweet, oily, musty odor. But as I said there isn’t always a noticeable smell.

Where Do German Cockroaches Hide?

I’ve mentioned before that I always look and find an infestation behind the refrigerator. The other place where I usually find them is on cupboard door hinges.

German roaches tend to congregate within 12 feet of where there is food and water and they need water on a daily basis to survive, so their harborage areas tend to be in the kitchen and bathroom.

As well as being nocturnal, they are also highly thigmotactic, which means they need to hide in confined spaces that will touch the top and underside of their bodies. An adult German cockroach can fit into a crack that is only 3/16″ (4.7 mm) wide, and nymphs can fit into even smaller cracks.^[5] This explains why they hide inside cracks and crevices, and in corrugated cardboard boxes.

They prefer porous surfaces such as wood and cardboard instead of surfaces like metal. I find many cockroaches hiding in kitchen appliances, drawers, and cabinets.

The following list also gives you other places you’ll find them:

• Behind and under the refrigerator, freezer, dishwasher, washer and dryer, stove/oven, water heater, kettle, microwave, and other appliances that have a motor to generate heat.
• Look in the dishwasher and stove
• Look under sinks for leaky pipes and where the pipes enter the wall
• Inside, underneath and behind cupboards, cabinets, and drawers and the corners of these
• Cracks around cupboards and drawers
• Cupboard and door hinges and frames
• Oven door hinges
• Behind cracks in baseboards and moldings
• In window frames especially if there is condensation on the windows
• In wall voids behind the sink, dishwasher, or oven
• In electrical equipment such as the TV, clocks, computer, and behind electrical sockets
• In the pantry, grocery boxes, and other food containers
• Trash cans
• Cracks in tiles

As German roaches are so small, they can hide their flat bodies in the smallest cracks and crevices.

These insects prefer warm, dark, quiet places and as long as they have access to the basic requirements of water, food, warmth, and shelter, they will be able to hide during the day undetected.

How Do These Small Cockroaches Get Into Our Homes?

People often think that roaches are only found in unclean homes, but this is not always the case. Having said that, good sanitization is vital when trying to keep your home cockroach-free.

However, it might not matter how clean you keep your home if you live in an apartment building because roaches can spread to nearby units through gaps around pipes and along utility lines.

German roaches are good at hitchhiking and usually enter your home with your deliveries, in your grocery bags, luggage, cartons, used furniture, and electronics.

What Are German Roaches Attracted To?

This species of roach cannot survive outside in the cold, so our homes provide the warmth and shelter that they need.

But just like other pests, they also need food and water sources to survive and the list is almost endless as to what can be an attractant because these roaches will eat just about anything.

In fact, German cockroaches need water more than food to survive. So limiting access to moisture and water sources should be a top priority.

Below are examples of some of these sources that act as attractants, but make sure you check out my more detailed list of what attracts cockroaches to your home so you can carry out a thorough inspection.

• Dripping or leaking faucet
• Dishes left in the sink overnight to soak
• Food and pet food left out overnight
• Spills not cleaned up
• Crumbs not cleaned up
• Standing water in the bathtub

Can German Cockroaches Make You Sick?

Roaches eat and crawl through all sorts of filth and rotting matter and pick up disease-causing bacteria and viruses on their spiny legs and bodies.

Although German roaches have not been documented to cause an outbreak of an illness, they are still considered a dangerous public health pest as evidence suggests they can spread 33 types of bacteria including E. coli and Salmonella which can cause food poisoning and diarrhea.^[6]

This is no surprise really because this insect will eat almost anything, and that includes other dead roaches, regurgitated food, and their own feces!

What other ways are roaches bad for your health? Well, you can also be allergic to the proteins in their droppings, shed skin, and saliva which can cause an allergic reaction and also trigger an asthma attack.

The allergens can cause:

• Itchy nose and eyes
• Wheezing
• Cough
• Stuffy nose
• Skin rash

Controlling German Roaches

The German cockroach is known as a common household pest and can be hard to treat. You now know that they are prolific breeders and they are the one pest that can cause a huge infestation fairly quickly.

• If you want to do your own cockroach pest control then start by excluding their entry points and hiding areas and eliminating their food and water sources, which you can find out about by reading what attracts cockroaches.

• Sticky traps will help you find where their harborage sites are as well as monitor their population level.

• Vacuuming is good for immediately reducing their numbers and will also remove their eggs and droppings. A vacuum with a Hepa filter is recommended to reduce the amount of airborne roach debris that can cause allergic reactions.

• Cockroach control products such as gel baits can be placed in small amounts directly in their harborage areas and in cracks and crevices. These baits are effective in killing german roach infestations. Again, more detailed information on how to use gel baits can be found by clicking on the link.

On the other hand, it is always best to get a licensed pest control professional to treat the infestation especially if you are seeing roaches in your home during the day. To get a free no-obligation quote, fill out the form below to get started. 

FAQs 

[1] https://www.pctonline.com/article/state-of-the-cockroach-control-market-sponsored-by-syngenta-july-2019/

[2] http://ipm.ucanr.edu/PMG/PESTNOTES/pn7467.html

[3] Pest Control Technology Technician’s Handbook

[4] https://www.cabi.org/isc/datasheet/9408

[5] http://ipm.ucanr.edu/PMG/PESTNOTES/pn7467.html

[6] https://www.pestworld.org/news-hub/pest-health-hub/the-truth-about-cockroaches-and-health/

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