How can I tell the difference between a German cockroach and an Asian cockroach?

The German cockroach (Blattella germanica) is one of the most ubiquitous pests on earth.  Originally thought to have originated in Europe, then Africa, the most recent theories surrounding its indigenous range trace it to Asia.  Today, it can be found on nearly every continent on earth (except Antarctica) and is almost always associated with human dwellings.

The species’ predilection for warm, humid environments make human structures, particularly areas where food is prepared, the perfect habitat for infestation.  Anywhere that humans are found, cockroaches are probably present too.  The Asian cockroach (Blattella asahinai), not to be confused with the Oriental cockroach (Blatta orientalis), has a more recent history of association with humans compared to German cockraoches.  To the casual observer, and even the seasoned pest management professional, the Asian cockroach looks nearly identical to the German cockroach.  They are closely related, but there are some key differences in behavior that make management methods different for the two species.

Asian cockroaches have longer and narrower wings compared to German cockroaches, along with a few other minor morphological differences.  The most obvious difference is the ability of Asian cockroaches to fly.  They are often attracted to lights and are most commonly found outdoors.  In North America, the Asian cockroach is currently known to be established in Florida, Georgia, South Carolina, North Carolina, Alabama, Louisiana and Texas, but has the potential to spread further throughout the United States because it can be established indoors.

I have a commercial customer with a large atrium inside the building.  I have collected multiple immature cockroaches that appear to be oriental cockroaches, but the adults I’ve seen have tan wings. The roaches seem to be living in the planters and mulched areas inside the atrium.  Any ideas what they are?

The insects in question are Surinam cockroaches (Pycnoscelus surinamensis), an exotic species that is established in the Gulf Coast states. In the northern parts of the United States, it is primarily a pest inside greenhouses and indoor atriums.  Adults are approximately 0.75 to 1.0 inch in length with wings that extend past the tip of the abdomen.  The cockroach is uniformly dark brown except for the front and side edges of the pronotum and wings which are light brown in color. The nymphs look a lot like oriental cockroaches, but upon closer inspection you will notice that the last five abdominal segments have a dull, rough appearance in contrast to the glossy sheen of the rest of the body.

Believe it or not, all of the Surinam cockroaches found in the continental United States are females.  It turns out that they reproduce parthenogenetically (without fertilization) resulting in the offspring being clones of the mother. No males have ever been observed for this species.  A closely related species, P. indicius is found in Hawaii and the Indo-Malayan region, and has both male and female forms.

Surinam cockroaches typically prefer to burrow into loose soil, leaf litter or mulch and remain hidden during daylight hours.  After dark, they emerge and feed on plant material, often causing substantial damage to plants in greenhouses and managed interior plantscapes.  Harborage areas are sometimes difficult to identify since these pests are known to burrow three to four inches deep and only emerge under cover of darkness or following heavy watering of potted plants.

When inspecting sticky traps, I noticed two projections off the back end of a brown cockroach.  What are these things and what purpose do they serve?

The projections you saw are called cerci, paired appendages and found on nearly every insect.  In some species, the cerci (singular: cercus) are large and pronounced; while in others they are reduced and hardly visible.  Given the discrepancy in appearance, you could rightly guess that they function differently for different insects.  In cockroaches, especially pestiferous species, cerci provide a valuable service in predator aversion.  Cockroaches love tight spaces, many of which allow cockroaches only to move forward or backward.  In this position, the cockroach can use its antennae and cerci to detect air movement and vibrations from ahead and behind.

The most prominent cerci in the insect world belong to earwigs.  Their cerci, commonly called pinchers, are used extensively in defensive behaviors, and will readily try to ‘bite’ you with them if handled.  The presence and activity of their cerci is most likely a major reason why earwigs are both detested and feared by homeowners.  For those identifying earwigs, this is a major feature used to separate species and even determine gender.  Some are toothed, some smooth, some cross over each other while others do not.