Brown Rat (Rattus norvegicus) vs. Black Rat (Rattus rattus) — How to Identify Them Correctly and Why It Matters

In everyday language, the terms "rat" and "brown rat" (or "sewer rat") are often used interchangeably. In reality, however, they refer to two different species of the genus Rattus with distinct morphology, ecology and behaviour. Correct identification is essential for choosing effective preventive and control methods.
In this article, we explain the most reliable identification features, describe the situation in the Czech Republic, and advise what to do if rodents are detected.

Why correct identification matters (common confusion and language issues)

Many people use the terms "rat" interchangeably when referring to different species, which often leads to confusion in practice — both in communication and in the selection of appropriate pest control measures.

Additional confusion arises from English terminology. In English, the general term "rat" is commonly used for both species and is then further specified by descriptive names:

• brown rat / Norway rat = Rattus norvegicus

• black rat / roof rat = Rattus rattus

However, this distinction based on "colour" is not entirely reliable. Individual animals may vary considerably in appearance depending on environment, age, or genetic variability, and their actual coloration does not always correspond precisely to the common name.

For this reason, professional and scientific texts recommend always including the Latin species name, which provides a clear and unambiguous identification.

Which species dominates in the Czech Republic?

In the Czech Republic, the more adaptable brown rat (Rattus norvegicus) has almost displaced the black rat (Rattus rattus), not only from urban environments. The occurrence of black rats is therefore rather local today, with reports more frequently coming from the northern parts of the country.

Brown rats live in close proximity to human settlements — typically in basements, sewer systems and food storage facilities. They are thus the most common pest problem in both agricultural operations and urban residential areas.

The presence of the black rat (Rattus rattus) is less common in the Czech Republic and is usually associated with specific local conditions, such as warmer areas, old wooden or poorly maintained roofs, barns, or historic buildings. Populations of black rats typically form loose social groups that may consist of several dozen individuals. These groups lack a clearly defined social hierarchy, and relationships between individuals, including breeding pairs, tend to be unstable and short-term.

From a dietary perspective, the black rat is omnivorous; however, under both natural and anthropogenic conditions it often prefers plant-based food sources. A significant part of its diet consists of fruit, vegetables, and various agricultural crops, which makes it a notable pest, particularly in agriculture and in storage and warehouse facilities.

In practice, most reports from family houses, apartment buildings and warehouses are therefore assumed to involve brown rats (Rattus norvegicus), unless the presence of black rats is clearly confirmed.

How to reliably distinguish them — a detailed overview of key features

Body structure and size

• Brown rat (R. norvegicus): robust, heavy-bodied animal with a broad chest and strong build; appears more "stocky".

• Black rat (R. rattus): slimmer and lighter build; adapted for agility and climbing, usually smaller than the brown rat.

Head, snout and ears

• Brown rat: blunt, broader snout; relatively small ears held close to the head; eyes smaller in proportion to the head.

• Black rat: distinctly pointed snout; larger, thinner ears (often almost translucent) that protrude noticeably — a very useful identification feature at close range.

Tail — a key identification feature

• Brown rat: tail shorter than the combined length of head and body; thicker, clearly scaly, sparsely haired and often appearing almost "bare".

• Black rat: tail longer than the body; slim, flexible, with finer scaling.

The tail is one of the most reliable features for identifying a live specimen.

Fur coloration

• Brown rat: grey-brown to brown-grey upper body with a lighter underside (grey-beige).

• Black rat: darker, often dark grey to black, usually uniformly coloured without a clearly lighter belly.

Note: Colour variations exist, especially in domesticated brown rats. Colour alone should therefore not be used as a sole identification criterion.

Behaviour and habitat preference

The brown rat is primarily a "ground-dwelling" species — it digs burrows, lives in basements, around building foundations and in sewer systems. It prefers moist environments, is an excellent swimmer and requires regular access to water. Dirty or contaminated surroundings do not deter it, and during winter it often enters buildings.

Brown rats are highly social rodents living in large colonies with a clearly defined hierarchy. A single colony may consist of dozens of individuals that cooperate in food searching, information sharing about risks and territorial defence.

A characteristic trait is their exceptional caution towards new food sources. New food is typically sampled in small amounts by less dominant individuals, often younger or weaker ones. Other colony members then observe their behaviour and health. If no adverse effects are observed, the food is considered safe and is consumed by higher-ranking individuals as well.

This phenomenon is known in professional practice as bait shyness. For this reason, second-generation anticoagulant rodenticides with delayed action, such as bromadiolone or brodifacoum, are used in professional rodent control. These substances do not cause immediate symptoms and significantly reduce the risk of bait avoidance developing within the colony.

Reproduction in brown rats (Rattus norvegicus) is not tied to a specific season and, given sufficient food and suitable shelter, can occur almost year-round. Females may produce multiple litters within a single year, with a gestation period of approximately just 21 days. A single litter can consist of up to 14 offspring, although the average number is usually lower. This combination of a short gestation period and a high reproductive rate is the main reason why brown rat populations can increase extremely rapidly, even in a geometric progression.

The black rat, by contrast, is a predominantly "climbing" species. It frequently inhabits attics, roofs, beams and wooden structures. It is an excellent climber, capable of moving along cables, trees and ladders. It prefers drier and cleaner environments (hay, barns, attics) and does not require water as frequently as the brown rat.

These behavioural differences strongly influence both the placement of baits and the choice of preventive measures.

Practical field identification checklist

• Check the tail — shorter than the body (brown rat), longer than the body (black rat).

• Determine the location of activity — basement/sewer vs. attic/roof.

• If possible, take close-up photographs of the head and tail.

• Observe droppings and tracks — their size and shape can be indicative.

• If in doubt, consult a pest control professional.

Implications for rodent control — why it matters to the client

Correct species identification has a direct impact on the choice of bait, placement of bait stations and preventive measures.
While roof and attic infestations require inspections at height and secure fixation of bait stations, basement and technical areas focus on sealing entry points, treating sewer connections, securing ventilation openings and protecting stored food.

Conclusion — key takeaways

• In the Czech Republic, the brown rat (Rattus norvegicus) clearly predominates; black rats occur only sporadically and locally, more often in northern regions.

• The most reliable identification features are the tail length, head shape, ear size, behaviour and habitat.

• If rodent activity is detected near agricultural facilities, in basements, or if burrows are found near sewer lines or tree roots (e.g. walnut or plum trees), the species involved is most likely the brown rat.