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Researchers to explore contraception for grey squirrels to tackle Lyme disease

Posted on 23 November 2023

Researchers will explore the effect of contraception on grey squirrel populations in a bid to control numbers and tackle the growth of Lyme disease around the UK.

A wild Grey Squirrel

Researchers will explore the effect of contraception on grey squirrel populations in a bid to control numbers and tackle the growth of Lyme disease around the UK. 

The study aims to discover if grey squirrels, which carry young ticks and are considered most responsible for Lyme disease transmission to humans, can be sustainably managed by using lethal and non-lethal methods.

It is part of a programme called ‘One Health approach to vector-borne diseases’being delivered by the Natural Resources Institute at the University of Greenwich, which has recently won a £1.25m grant from UK Research and Innovation (UKRI) and its partners, which include the University of York. 

Native species

Grey squirrels are one of the most common small animals present in woodland and are host to both ticks and Lyme disease. The grey squirrel is an invasive species in the UK which displaces the native red squirrel and costs the economy £37 million per year by bark stripping trees. Efforts to protect red squirrel populations by controlling grey squirrels are under way in many parts of the UK and have wide public support.

Caused by a bacterial infection, early symptoms of Lyme disease include a rash, fever and pain. The infection can seriously damage the nervous system if left untreated. Lyme disease is well established in the north-eastern parts of the United States, and is growing in the UK and across many parts of Europe.

People acquire the disease from the bite of infected ticks searching for a blood meal. Ticks feed on a range of wild animals but also on humans walking through the countryside and the woodlands. Ticks don’t fly, so they wait for animals to walk by, jumping on to anything that disturbs the vegetation they are waiting on. Adult ticks often feed on deer, but younger stages usually feed on smaller animals, particularly rodents such as squirrels. It is these immature stages of ticks that are the most dangerous in terms of Lyme disease transmission to humans.

Rising cases

The exact woodland locations where the research will take place have yet to be confirmed. 

The programme between UKRI and the Department for Environment, Food and Rural Affairs (Defra) includes Dr Giovanna Massei, a Senior Research Fellow at the University of York and Europe Director of the Botstiber Institute for Wildlife Fertility Control.

Dr Massei said: “Lyme disease is a growing problem in the UK, statistics show cases are rising around the country. Because deer and other wild animals, like squirrels, carry the ticks which spread the disease, we hope this study will help us to understand the interconnections between the health of people, animals and ecosystems.” 


The UK's Net Zero 2050 policy contains bold plans to plant millions of trees each year to expand landcover in woodlands and forests, not only helping to sequester carbon but also contributing to lower local temperatures as the climate changes. This is vital for climate action, but these changes in land use have implications for the spread of non-native species and disease.

This complex issue is at the heart of this research. Dr Massei added: “We want this research to produce evidence-based recommendations for minimising the risks of tick-borne disease which could occur through rewilding and reforestation. I’m proud the University of York can be part of this impact-focused research into squirrel populations, which could transform human health in the years to come.”

Some experts have argued that the removal of grey squirrels by itself could result in a reduction in Lyme disease risk, but this has not yet been proven. This is because ticks can feed on other wild animals and it is not clear what will happen when grey squirrels are removed in terms of disease risk. 

Climate change

This project plans to answer this question by determining what happens when grey squirrel populations are being reduced, and how this affects ticks and diseases. It will also develop models to predict what could happen to grey squirrel populations, and the ticks and diseases they host, as a consequence of increasing woodlands and forests in the UK while the climate is also changing.

The research is headed by Professor Steven Belmain and Dr Dan Bray at the Natural Resources Institute, University of Greenwich and involves a co-investigator team of researchers based at the same university (Dr Dan Bray), University of Salford (Prof Richard Birtles), the University of York (Dr Giovanna Massei), the Animal and Plant Health Agency (Dr Simon Croft) and Forest Research (Dr Harry Marshall).

Prof Belmain said: “Our research aims to build on these ongoing activities to control grey squirrels, helping to understand the role of greys in perpetuating Lyme disease and seeing whether reducing the population of greys can also reduce the prevalence of ticks and Lyme disease. We hope to show that grey squirrels can be sustainably managed in humane ways by non-lethal methods that will lower their population, helping the smaller red squirrel population to recover and expand so that more people can appreciate reds in the wild whilst reducing the chances of catching Lyme disease.”

public engagement 

The team will engage with the public throughout the project, particularly with groups trying to save the red squirrel through grey squirrel control. The project team will also explore the attitudes of the wider public towards squirrels, ticks and infections such as Lyme disease. This is an essential step toward understanding people's concerns about animal control, and how best to protect people from vector-borne disease in a changing environment and climate.

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