UK Species of Rats

The Norway Rat - Rattus Norvegicus

The Norway Rat, Brown Rat, or Sewer Rat, whatever you like to call it - even “the common Rat,” is a sly, aggressive and extremely adaptable mammal.

Since the arrival of these Rodents to our shores in the 1700’s arriving on trade ships from the Orient, there has been a human hatred of them ever since, yet still they thrive in all of our villages, towns and cities.

The Norway Rat exists with good success as a feral animal and more successfully as a commensal animal that thrives by living alongside human populations all over the UK and the world.

Rats construct nests in burrow systems just as easily as they can utilize most structural elements of human construction, and are even adaptable to surviving in our sewer system’s at a very high success rate.

When home ranges are short and food sources are in abundance, daily movement for the Brown Rat will be limited. The Brown Rat is an omnivore and is just as happy to be feeding on human foods and waste, or by utilising available natural food including insects, snails and plant foods. 

Where well established colonies exist, mature adult rats will exhibit neophobic behaviour and avoid traps, bait stations, containers and will even avoid new foods that suddenly appear in their environments.


A relatively large Rat, the Norway Rat has course brown fur on its upper body with light to dark grey fur covering its under belly and weighs in at between 300-400g. The average adult measures 41cm from the tip of its nose to the end of its tail although much larger specimens have been reported leading the to the term “Super Rats!” However, if one uses the comparison of a good Fisherman’s tale, the sightings and claimed size of these mythical creatures are usually somewhat exaggerated.

The Norway Rat has a long almost naked scaly tail which is shorter than its body, whereas the Roof Rats tail is longer than its body, thus allowing professional pest controllers an easy way to separate the two different Rat species.

Life cycle of the Brown Rat

Although there are many factors to consider, the reproductive peaks of the Brown Rat occur throughout the spring and during the Autumn. However, our homes and businesses provide the perfect environment and ideal conditions for breeding to occur all year round. On the other hand, colonies that are established outdoors will see a significant decrease in breeding during cold winters and hot summers.

Following successful mating and a gestation period of about 22 days, the female Rat produces on average litter sizes of between 8-10 pups, although larger litters of up to twelve pups can be produced.

Naked and totally blind at birth, the female Rat tends to her young for a period of about nine to fourteen days before their eyes open and are weaned for the following ten to fifteen days. Once weaned the young Rats begin to take short exploratory trips out of the nest learning from their mother through imitation as a means to discover their surroundings, memorise pathways to food sources, hiding places and burrow entrances for example. The young Rats reach sexual maturity in eight to twelve weeks.

Female Rats can come into heat every four to five days and mate within days of a litter being born. Although litter sizes depend highly on the availability of food sources and other key factors, the female can ultimately wean more than twenty offspring if she survives for a year or more. However, wild Rats living in our towns and cities normally live on average between five and twelve months, whereas Rats in captivity have an average lifespan of between three to four years.

The Roof Rat, or Black Rat - Rattus Rattus

The Black Rat was once the dominant Rat species currently known in the UK and was once a very important pest thriving in many UK coastal cities and ports. Upon the arrival of the Norway Rat, Black Rat populations plummeted whilst Brown Rat populations grew rapidly and have thrived ever since.

Although numbers of Back Rats are much lower today than they were many years ago, they can still be found in and around UK coastal settlements, and, where professional pest control is concerned, they are still considered a serious pest. As the name suggests, the ‘Roof Rat’ prefers to dwell in and around the upper reaches of industrial buildings, treetops and our homes. Living as a creature of the night, this sleek, agile, extremely efficient climber and navigator of overhead wires and ledges can often go unnoticed for long periods due to its secretive and elusive nature.

The Roof Rat is also known to frequent loft’s and attic’s in coastal urban areas where lush vegetation and fruits are found. They easily travel in order to establish nests above normal human perspective living amongst the cover of bushes, trees and other thick vegetation and are as equally adapted to man’s environment as they would be living outdoors feeding on slugs, insects, wild fruits and plant materials. However, when the constant food source and more favourable living conditions offered by humans is available, the Black Rat would inevitably choose this option.

The Roof Rat is a highly intelligent creature with Neophobic tendencies on a much higher level to that of the Brown Rat, and as such, baits, bait stations and traps may be avoided for long periods.


The Roof Rat has typically black to tawny brown fur covering its upper body and lighter fur covering its underbelly and weighs in between 150-250g. The average adult measures about 41cm in total length from the tip of its nose to the end of its tail. This is approximately the same length as the Norway Rat. However, the Roof Rats tail, measuring about 11cm, is longer than its body, whereas compared with the larger robust Norway Rat whose tail is shorter than its body. The Norway Rat also has shorter ears and a blunt snout.

Life cycle of the Roof Rat

As with the Brown Rat, the Roof Rats success and reproductive potential is highly dependent on available food sources, harbourage and other key factors.

Slightly less prolific that the Brown Rat, the female Roof Rat can produce 3- 4 litters with an average of four to eight pups per litter. After a period of about 4-5 weeks, the young Roof Rats will forage outside of the nest and are sexually mature in approximately 12 weeks. Breeding peaks are much the same as the Brown Rat, occurring in the spring and Autumn, and again, as with the Brown Rat, under good conditions Roof Rats will breed all year round. Although key factors have a significant part to play, most adults live between five months to one and a half years.

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