A large species of cockroach detected for the first time in Finland – thrives in human surroundings

A cockroach measuring over three centimeters in length was found in early December in the Oulu region and was delivered to Marko Mutanen, the senior curator at the University of Oulu. He identified the individual as a smokybrown cockroach, scientifically known as Periplaneta fuliginosa. This shiny dark brown cockroach species has not been previously identified or reported in Finland.
Periplaneta fuliginosa eli savutorakka
The smokybrown cockroach is approximately three centimeters in length. There's no need to worry about a single individual, but if you find another, it is reason to suspect that the smokybrown cockroach has successfully reproduced (photo Marko Mutanen).

Finland is home to two native cockroach species, and indoors, the German cockroach is most commonly encountered nowadays. Globally, there are several large cockroach species that live in association with humans, and occasional individuals are encountered in Finland, especially the American or brown-banded cockroach.

The smokybrown cockroach is a relative of the brown-banded cockroach, and it has become a nuisance in human dwellings in some parts of the world. Especially in Japan, Australia, southern North America, and some parts of South America, the smokybrown cockroach has spread to human habitations, where it thrives, particularly in the damper and warmer areas. Like other cockroaches, it feeds on a variety of organic waste, including human food. Similar to other cockroaches, the smokybrown cockroach contributes to unhygienic conditions, spreads diseases, and causes allergic reactions and asthma. However, it is not considered a direct threat to buildings. "The smokybrown cockroach does not seem to be a harmful invasive species, as it does not threaten native species, but it can be classified as a pest species," Marko Mutanen assesses.

The smokybrown cockroach has likely arrived in Finland through human activities, most likely through international transportation. The presence of the smokybrown cockroach in Finland exemplifies a significant global issue where globally transported goods carry unwanted species at an accelerating pace. With climate change, newcomers can survive and adapt to Finnish conditions. Recently, there have been reports, for example, of the rapid spread of the paper silverfish (also known as gray silverfish or long-tailed silverfish) in Finland, a species that was able to adapt worldwide through transported corrugated cardboard.

"To date, there are only a few observations of the smokybrown cockroach in Europe, but in reality, it may already be widely distributed as a companion species to humans, especially in Southern Europe," Mutanen estimates. The species has not yet been able to effectively spread to cooler regions.

"There always seem to be suitable conditions for different species in human dwellings," Mutanen reminds. The smokybrown cockroach could thrive, for example, in large building complexes, cities, and sewer networks. "The smokybrown cockroach is a conspicuous creature and is easily found. There's no need to worry about a single individual, but if you find another, it is reason to suspect that the smokybrown cockroach has successfully reproduced," Mutanen advises.

The composition of species accompanying humans changes rapidly as some species disappear and others thrive, depending on how human living conditions vary and develop in different regions. In Finland, many species that were once common in residences, such as the German cockroach, have become rare as others take over.

At one time, Swedish cockroaches were present in Finnish residential buildings everywhere. However, the brown rat was an effective predator of the Swedish cockroach, and as a result, the Swedish cockroach practically disappeared, after which the German cockroach took over. Rats remain a companion species to humans in Finland. The natural enemies of the smokybrown cockroach are rats, viruses, and parasitic nematodes that infest cockroaches.

Ecology and Genetics Research Unit at the University of Oulu

Last updated: 8.12.2023