The rise of rats in Hong Kong

Scurrying in the shadows, lurking in sewers or hiding in caves, you can be sure that there are almost certainly rats anywhere there are people.

Known for their fierce survival instincts, brown rats prefer to build their burrows in urban sewers and the dwellings of humans, eating one-fifth of foodstuffs planted yearly, but contaminating far more. In major cities like London and Birmingham, some experts say there are as many rats as there are people, while more conservative estimates put the ratio closer to one rat for every four humans. To fully understand how the rise of the rats has happened, you must understand the staggering rate at which rats can reproduce.

How fast can rats reproduce?

Rats are indeed prolific breeders, and their ability to reproduce quickly is one of the reasons they are formidable pests. Here's an updated and sourced overview of their reproductive capabilities, focusing on the Norway rat (Rattus norvegicus), which is one of the most common species encountered in many parts of the world.

Key Takeaway:

• Rats have 7–8 young per litter, and between 3–6 litters a year.
• The gestation period is about 3 weeks (21-23 days).
• It only takes 10–12 weeks from birth to reach sexual maturity. 
• The lifespan of a rat is about 1 year. 

Taking into account the survival rate of the offspring, the actual number of descendants from a single pair of rats can vary. However, if we assume a high survival rate and that all offspring are able to reproduce, the number of rats descended from a single pair could grow into the hundreds within a year, and potentially into the thousands within a few years, assuming no constraints such as food scarcity, predation, disease, or human control efforts.

How many pups will rats breed each time?

1. Sexual Maturity: Norway rats typically reach sexual maturity at about 5 weeks of age, but they may not breed until they are 3 months old or more, depending on environmental conditions.

2. Gestation Period: The gestation period for a Norway rat is around 21 to 23 days.

3. Litter Size: A female Norway rat can give birth to a litter of 6 to 12 pups, although larger litters are possible.

4. Frequency of Litters: A female rat can breed throughout the year if conditions are favorable, and can produce up to 5 litters per year. After giving birth, a female rat can come into estrus and mate again within 48 hours.

5. Annual Reproduction: Given the gestation period and the time it takes to wean pups, a female rat could have around 5 litters per year under optimal conditions. With an average of 8 pups per litter, this could theoretically result in 40 new rats per year from a single breeding pair. 

Click to know more about rat species and their habit.

Why don’t rats outnumber people?

The speed at which rats can breed is frightening, but there are many factors that help to stop a population from exploding out of control. In a real-world scenario, the death rate usually increases as the size of the rat population grows. Whenever food or space is limited, mortality is higher, which partially keeps the rate of population growth in check. 

The main reasons for rat population reduction:

• Lack of food and shelter
• Disease
• Predation
• Pest control
• In-fighting
• Cannibalism

How many rats are there in Hong Kong?

New York City has one of the highest populations of brown rats in the U.S. Researchers from New York estimated that there are approximately 3 million rats in the city as of 2023, finding that the number had increased by 42 percent in the past decade.

Given the human population of New York City is 8.468 million in 2021, if we assume the rat-human population ratio is the same in Hong Kong, there are approximately 2.5 million rats in Hong Kong. 

Which businesses are most likely to be affected by rats?

Based on over 100 enquiries made to Rentokil.

Worried about rat infestation?

Found signs of rat infestation at your premises? Don't worry. At Rentokil, we can offer industry-leading effective rat pest control solutions including rat tracking, rat proofing, rat baiting, and pest disinfection.

Call Rentokil Hong Kong today on +85229546888 for your home or business or contact us to schedule an on-site inspection to get rid of rats safely and effectively as required depending on the situation.

Why Rentokil Initial?

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