Dealing with rat infestation
Rat infestations in the UK have been increasing in many areas in recent years. The causes are manifold - environmental, infrastructural, behavioural, and biological - so mitigating them also requires a multi-pronged approach.
One of the causes of increased rat infestations is that warmer winters reduce rat mortality, enabling more individuals to survive through the colder months. Higher than average temperatures can extend breeding seasons.
And there is abundant food waste, poor waste management and a takeaway culture. The presence of more restaurants, takeaways, food delivery, and disposable food packaging leads to more food waste in public bins, streets, and back alleys, which rats exploit. Overflowing or poorly sealed bins, irregular or infrequent waste collection, and litter or fly-tipping provide easy food sources.
Rats exploit faults in sewers, damaged drainage systems, unsealed joints, disused pipework, and open manholes to access buildings or move underground. Much of the UK’s sewer network is old (some from Victorian or early 20th century), with materials or joints that degrade over time, giving rodents more ingress routes.
Rats reproduce quickly: multiple litters per year, with many offspring, and sexual maturity reached early. This allows populations to expand swiftly if conditions are favourable. In some areas, rodent populations are becoming resistant to common rodenticides, making control more difficult.
Cuts to street cleaning, delayed bin collections, fewer pest-control staff or fewer proactive measures can create local hotspots. Some councils no longer offer pest control or charge fees, making responsiveness uneven.
Some individuals, households, or businesses may not follow best practices (e.g. leaving food out, poor waste containment, neglecting repairs). Even if the majority do well, a few poor practices in a given area can undermine the collective effort, because rats are mobile and will exploit “weak links.”
Because of the multiple causal factors, effective mitigation requires coordinated action at individual, local authority, infrastructure, regulatory, and technological levels. Good food hygiene would include waste management with secure bins, the prompt removal of food waste, and not putting cooked or greasy waste into drains. There would need to be frequent and reliable waste collection to ensure bins in high-risk zones are sufficient and well-maintained
Genetic modification (GM) and related biotechnologies are increasingly being explored as next-generation methods of rodent control, aiming to reduce populations more sustainably and humanely than poisons or traps.
Genetic modification could reduce fertility or reproductive success via engineered genetic elements that spread themselves through a population faster than normal inheritance, ensuring nearly all offspring inherit a chosen gene. Scientists could insert a sterility gene, for example, one that disrupts sperm or egg formation, and attach it to a gene drive so that it quickly spreads through a rat population. Over several generations, this could cause the population to crash naturally as more individuals become infertile.
CRISPR-based ‘X-shredders’ could distort sex ratios by destroying X chromosomes in sperm, producing mostly male offspring, leading to a rapid decline in breeding females. Targeted reproductive gene knockouts might disable key genes like Prdm9 or Zp3 essential for gamete development.
Genetic edits could be used to make populations overwhelmingly male, leading to a natural reproductive bottleneck. This could slow population growth drastically while maintaining ecosystem balance more predictably than eradication methods.
We might engineer rats that could not digest certain food waste types, reducing their success in cities. We could make rats susceptible to specific harmless biocontrol agents, for example, engineered microbes that only affect rats.Introducing genes that reduce aggression or nesting behaviour, would make them less likely to thrive near humans.
GM-based control avoids poisoning, which causes prolonged suffering and risks secondary poisoning of predators. And once released, a gene drive could persist and spread without continual human intervention.
Imperial College London’s ‘Target Malaria’ project uses similar gene drive approaches on mosquitoes; not rats yet, but the science is transferable. CSIRO (Australia) and New Zealand’s Predator Free 2050 programme are investigating gene drives for rodents on islands, where containment is easier.
Genetic modification could, in principle dramatically reduce rat fertility or alter sex ratios, and do so humanely and species-specifically. It offers potential long-term, sustainable control.
While there would be objections, as there are to all scientific progress, the alternative is for an increasing rat population. Humans have accidentally wiped out or limited several species, but doing one deliberately would be an improvement.
Madsen Pirie