We used to think the oriental cockroach (Blatta orientalis) was rare. In fact, to naturalists it was of interest to encounter this species rarely.

It was recorded in 1955 by Guido Lanfranco, and since then a handful of records are available. We have managed to find the species in one locality in Gozo and in another in Comino, but the data was based on single individuals. In 1997, stable populations lived in Għadira where the occasional individual was found.

As from 2014 our studies and records from customer services shows that the species is on a steady increase in the north of Malta, especially in the Mellieħa, and it seems the species is replacing the common nuisance pest, the American cockroach, where the latter species is thriving.

The oriental cockroach, also known as the waterbug, is a large species of cockroach; adult males range between 18 and 29mm and adult females are 20 to 27mm long. It is dark brown to black in colour and has a glossy body. The female looks different from the male, appearing to be wingless at first glance, but it has two very short, useless wings just below its head.

The oriental cockroach tends to travel slower than other species. They are often called waterbugs since they prefer dark, moist places. They can often be found around decaying organic matter and in sewers, drains, damp basements, porches, and other damp locations. They are major household pests in parts of England and the US.

Originally endemic to the Crimean Peninsula and the region around the Black and Caspian Seas, its distribution is now cosmopolitan. In order to thrive, the cockroaches need places to hide and prefer warm and relatively humid places; they also need a source of food and liquid.

The optimum temperature for oriental cockroaches is between 20°C and 29°C.

It seems the species is replacing the common nuisance pest, the American cockroach

It can be elusive in that a casual inspection of an infested dwelling during the day may show no signs of roach activity.

The species is also harder to get rid of than other roaches. Adults cannot be controlled by normal application of residual insecticide, and since they live in wet areas the insecticides can get washed away, and two months later females can hatch new nymphs.

Besides this species, 10 other are known to exist in the Maltese islands, two of which are recorded as new locally while two others are new to science.

The other recorded species are the American cockroach (Periplaneta Americana – Wirdiena Ħamra), German cockroach (Blattella germanica – kokroc tal-faxx), the brown-banded cockroach (Supella longipalpa – kokroc isfar, the Egyptian cockroach (Polyphaga aegyptiaca – wirdiena sewda, the field cockroach (Loboptera decipiens – wirdiena ta’ l-għelieqi) and the wood cockroach (Ectobius kraussianus – wirdiena tal-Buskett).

If left unchecked in urban areas, this species of cockroach may be problematic. Oriental cockroaches can be a source for many food-borne pathogens, including E. coli, Salmonella and others. Due to their dietary preference for garbage and decaying organic matter, oriental cockroaches can carry these patho­gens on their legs and bodies from contaminated areas and then transmit them onto clean surfaces.

Arnold Sciberras is a pest entomological consultant and Jeffrey Sciberras is a pest botanical consultant. For further information call Fort Pest Control on 9999 1123 or e-mail info@fortpestcontrol.com.

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