Brown rat
Rattus norvegicus
Llygoden mawr
Status:
Common rat, Norway rat, Sewer rat
Thought to be widespread in Snowdonia, associated with farm buildings, towns and villages and coastal habitats. The brown rat is a non-native species, with its origins in central Asia, it spread across Europe and into the British Isles during the 18th Century, accidentally transported in the cargo of boats and ships. It is also known by the names of: common rat, Norway rat and sewer rat.
The species has no legal status in the UK and is still classed as vermin. In fact, it is almost universally hated and reviled by humans throughout its range being considered as a pest of crops and stored food and as a vector for human diseases. In the UK, Leptospirosis is possibly the most common disease transmissible to humans but elsewhere they can carry plague, typhus, Q-fever and Hantavirus.
There are an estimated 6.79 million pre-breeding brown rats across the UK. Numbers fluctuate from year to year depending on where the rats are found and the availability of food. Prolonged and severe winter conditions are known to knock back the numbers of rats living entirely outdoors, whereas those associated with urban areas and farm buildings may continue to thrive. In sheltered locations with an abundant supply of food the brown rat will breed all year round. In more rural situations the species has a distinct breeding season from June – October. As a rodent they are short lived (rarely surviving more than 2 years) but are highly fecund with a single female producing an annual litter rate of 5 with a mean litter size of 9 babies. The population therefore has an annual increase to peak numbers each October.
In Snowdonia the species has almost certainly been under-recorded and surveys targeting farms and outbuildings, rubbish tips and towns and villages would produce more records.