It is unclear how the rat made its way to Europe due to insufficient data, although a land route seems more likely based on the distribution of European haplogroup "A".

[12] However, recent studies have called this theory into question and instead posit humans themselves as the vector, as the movements of the epidemics and the black rat populations do not show historical or geographical correspondence.

[13][14] A study published in 2015 indicates that other Asiatic rodents served as plague reservoirs, from which infections spread as far west as Europe via trade routes, both overland and maritime.

[15] The black rat originated in India and Southeast Asia, and spread to the Near East and Egypt, and then throughout the Roman Empire, reaching Great Britain as early as the 1st century AD.

[18] Black rats are thought to have arrived in Australia with the First Fleet, and subsequently spread to many coastal regions in the country.

[20] In urban areas, they prefer to live in dry upper levels of buildings, so they are commonly found in wall cavities and false ceilings.

Their nests are typically spherical and made of shredded material, including sticks, leaves, other vegetation and cloth.

Black rats are considered omnivores and eat a wide range of foods, including seeds, fruit, stems, leaves, fungi, and a variety of invertebrates and vertebrates.

They are generalists, and thus not very specific in their food preferences, which is indicated by their tendency to feed on any meal provided for cows, swine, chickens, cats and dogs.

They are also a threat to many farmers, since they feed on a variety of agricultural-based crops, such as cereals, sugar cane, coconuts, cocoa, oranges, and coffee beans.

[26] Through the usage of tracking devices such as radio transmitters, rats have been found to occupy dens located in trees, as well as on the ground.

Rats appear to den and forage in separate areas in their home range depending on the availability of food resources.

[25] Research shows that, in New South Wales, the black rat prefers to inhabit lower leaf litter of forest habitat.

A number of bacterial diseases are common to rats, and these include Streptococcus pneumoniae, Corynebacterium kutsheri, Bacillus piliformis, Pasteurella pneumotropica, and Streptobacillus moniliformis, to name a few.

In addition to agility, the black rat also uses its keen sense of hearing to detect danger and quickly evade mammalian and avian predators.

For example, research conducted by Hoffman et al. indicates a large impact on 16 indigenous plant species directly preyed on by R. rattus.

In many cases, after the black rat is introduced into a new area, the population size of some native species declines or goes extinct.

This is because the black rat is a good generalist with a wide dietary niche and a preference for complex habitats; this causes strong competition for resources among small animals.

This has led to the black rat completely displacing many native species in Madagascar, the Galapagos, and the Florida Keys.

By eradicating the black rat populations in Australia, the diversity of fungi would decline, potentially doing more harm than good.

[38] Large-scale rat control programs have been taken to maintain a steady level of the invasive predators in order to conserve the native species in New Zealand such as kokako and mohua.

[39] Pesticides, such as pindone and 1080 (sodium fluoroacetate), are commonly distributed via aerial spray by helicopter as a method of mass control on islands infested with invasive rat populations.

[42] Eradication projects have eliminated black rats from Lundy in the Bristol Channel (2006)[43] and from the Shiant Islands in the Outer Hebrides (2016).