PPDL Picture of the Week

January 21, 2020

German cockroach, photos are rare!​

Tim Gibb, Extension Entomologist, Purdue University

A cockroach is not very photogenic, at least I rarely have photos sent to me here in the pest diagnostic laboratory.  I can think of several reasons why a roach may not be photographed very often.   'Flat out ugly' is probably the biggest single reason but the unpleasant living conditions where they thrive is also reason for lack of photos. Nobody want a photograph of that.

Cockroaches require only food, water and a warm place to harbor in between regeneration events. They masters at being able to to eat whatever food becomes available to them. They commonly forage on stored foods, pet foods and table scraps that may be lying around but also on uncleaned dishes or in dirty garbage receptacles. 

Cockroaches are sneaky. They usually only come out at night when no one is around, which does not endear them to most people. But their signs are unmistakable and they emit a uniquely unpleasant smell if they have been around a while. So again, with such a disgusting life style who would possibly want a photo, especially of one feeding in your kitchen where you live. The fact is that most people typically go to excessive lengths to avoid them and if found, eradicate them from their homes. 

The German cockroach one of several species that can be found inside homes but it is the species that gives all other cockroaches a bad name. It occurs throughout the world primarily in association with humans and often plagues multifamily dwellings in the United States. Because it does not directly harm people by biting them, it is considered a filth pest, and the action threshold for this insect depends upon the tolerance of the people living in the infested dwelling. That is why infestations in multifamily dwellings are so common. The building is subject to the highest common tolerance level. If one apartment remains home to a large infestation, the entire building remains infested -regardless of control efforts in other areas.

The German cockroach has three life stages, typical of insects with incomplete metamorphosis: egg, nymph, and adult.  Adult German cockroaches are generally about 5/8 inches in length, are light brown except for the shield behind the head that is marked with two dark stripes running lengthwise to the body. They have long antennae and can run in short bursts very quickly. Eggs are enclosed in capsules that are light tan and usually yield about 36 young. Young roaches are wingless and nearly black with a single light stripe running down the middle of the back.

The entire life cycle is completed in about 100 days and, under ideal conditions, population growth has been shown to be exponential – another reason why they gross people out.

Many classes of insecticides, including organophosphates, carbamates, pyrethroids, amidinohydrazones, insect growth regulators, inorganics, microbials, and botanicals, are available for controlling German cockroaches. These come in a wide variety of formulations including baits, sprays (emulsifiable concentrates, wettable powders, microencapsulates), dusts, and powders.

Baits and baiting technology have recently been improved such that roach infestations can be eliminated rather than just reduced in many buildings. Homeowners should also consider the following tactics.

  • Nontoxic and low toxic alternatives for German cockroach control are readily available to homeowners.
  • Sticky traps can be used to monitor or reduce population size. 
  • Improving sanitation by eliminating food, water sources and clutter can have a significant impact on reducing populations.
  • Exclusion practices such as sealing cracks and crevices will reduce harborage space and thus infestations.

Often a combination of the above tactics are required to effectively manage an existing roach infestation. After the roaches are eliminated, sanitation and exclusion techniques usually are sufficient but should be continued to keep them at bay.

A nicely cleaned, uncluttered and healthy kitchen area is the goal. That is when a photo is warranted.


​Click image to enlarge

German cockroach