Controlling grey squirrels by trapping and shooting is no doubt helping to keep red squirrels alive. However, this is happening at a local level, around red squirrel colonies, in an effort to keep the grey numbers as low as possible near the reds.
This prevents the greys from monopolising the food in these areas and reduces the risk of them passing squirrel pox to the reds. Beyond these areas, grey squirrels are largely left to prolifically multiply so just keep migrating in to where the remaining red colonies are struggling to survive. Red squirrel conservation groups are fighting a losing battle so some sort of national intervention is desperately needed.
Oral Contraceptive for Grey Squirrel Control
Research and development in to a contraceptive drug to be fed to grey squirrels was began by UK Squirrel Accord back in 2017. The five -year programme was set out in to the following stages: 1. Research and Development 2. Landscape-scale trials 3. Registration 4. Widespread Rollout. Covid delayed the programme by a year, so the landscape-scale trials were delayed until 2024.
Sadly, in 2024 UK Squirrel Accord announce that the oral contraceptive had failed and they estimated that it would take a further ten years of development to get it to work. So, it might be ready by 2034. Maybe earlier if the reds are very, very lucky.
Gene Drive Therapy
In a nutshell, gene editing techniques could be used to cause grey squirrels to only produce infertile females. This genetically altered trait would be ‘driven’ through the population as they bred, so that over time no females capable of producing young will be available and the population will naturally die out. Or, gene editing can be used to cause all offspring to be male, therefore, breeding females will disappear and again the grey population would die out.
Although the technology exists, there are many hurdles to overcome before it could be introduced. In 2024, the Roslin Institute estimated, if funds were ever made available, it would take approximately £10,000,000 and ten years to develop a gene drive therapy for grey squirrels. As of 2025, there are no plans by anyone to start one.
Pine Marten Introductions
Correlations between pine marten population increases, red squirrel population increases and grey squirrel population decreases have been recorded for several years now. Over recent years, red squirrels in Ireland have been making a strong comeback, with the grey squirrel populations declining, and this is mostly attributed to the growing pine marten population. Pine martens are increasing because their persecution is being more strictly policed in Ireland.
Local pine marten reintroductions in to red squirrel areas is a controversial subject. Pine martens also eat red squirrels, so a red squirrel population would need to be big enough to cope with the losses, while waiting for the grey population to be sufficiently affected to the allow the reds the free habitat to increase their numbers. A big question is how many red squirrel populations are left which are big enough to cope!