You’ve just brushed your dog and collected a fluffy handful of fur. Instead of tossing it away, you leave it out for the birds, thinking you’re giving nature a helping hand. But what if that well-meaning act is actually harming the very wildlife you’re trying to help?
WE ALL WANT TO HELP WILDLIFE
As urban development takes hectare after hectare from nature, wild animals are forced to adapt. You might be familiar with the case of birds opening milk bottles to get at the cream1, or gulls and foxes making a mess while helping themselves to our rubbish. Yet, while these activities can be a source of conflict between humans and wildlife, many of us crave a connection to the wild in one form or another. So, we plant wildflowers, install bee hotels and bird feeders, build ponds, and when our pets shed fur, we hang it outside in the hope that birds will use it to line their nests. There is no denying, our hearts are in the right place! But sometimes, good intentions aren’t enough.
BEE-KILLING PESTICIDES STILL USED ON PETS
Fipronil and imidacloprid might sound like characters from a sci-fi film, but they’re two real-life villains in this story. Originally hailed as a wonder pesticide and a promising new way of controlling crop pests, these chemicals became widespread across farms in the 1990s. However, by 2018, both had been banned throughout EU agriculture after studies revealed they were having devastating effects on wildlife.
Sadly, the chemicals were not only killing pests, but pollinators and other wildlife too! For example, as insect-eating birds consumed the sprayed insects, the chemicals started to build up in the food chain, causing chick deformities and death.2,3
So, you would assume with all of this evidence, our wildlife and birds would now be safe from fipronil and imidacloprid! But, unfortunately that’s not the case because the ban only applies to farms. These chemicals are still widely used in pet flea treatments. So, unlike wild animal fur, pet fur is often laced with insecticides designed to linger for weeks or even months. So, when you hang that fur outside, you might also be offering birds a dose of poison.
SCIENTISTS TEST NESTS FOR HARMFUL CHEMICALS
To confirm whether veterinary flea treatments might be inadvertently harming our garden birds, a research team comprising of scientists from the University of Sussex and the University of Neuchâtel (Switzerland) examined 103 nests made by blue tits and great tits to tested them for traces of 20 different insecticides.
To do this, the team took 25mg of fur from each nest and mixed the samples with solvents, which would reveal the presence of any chemicals.
SCIENTISTS’ FEARS CONFIRMED
The results confirmed the teams’ fears: each nest contained between 2 and 11 insecticides, and overall, 17 different insecticides were detected!
Equally, despite the agricultural ban having been in place for years, fipronil was found in every nest, and imidacloprid in more than 80%.
But what impact was this having on birds?
Well, thanks to the team of volunteer citizen scientists who had collected the nests, the researchers already knew some information about the nests, like where the nests came from, how many unhatched eggs and dead chicks had been observed in the nests before they were collected, and whether the nests were from blue tits or great tits.
From this they could tell that the great tit nests with higher numbers of insecticides present had significantly higher numbers of dead chicks and unhatched eggs, with a similar trend observed among blue tits. Similarly, nests found in urban areas were associated with higher concentrations of insecticide and higher chick mortality than those in rural areas, suggesting that proximity to high numbers of household pets did indeed pose a threat to breeding birds.
Importantly, the team also noted that both blue tits and great tits tend to clean dead chicks and eggs from the nest to keep the other chicks healthy, meaning that the impact of insecticides could be even greater than recorded.
THE PICTURE IS CLEAR
Fipronil and imidacloprid have not been used in agriculture since 2013 and 2018 respectively, but their presence in pet treatments still harms our precious wildlife.
However, pet fur is not the only way these chemicals can be spread! Insecticides make their way into our rivers when water from your pet’s bath is not purified properly, or when your dog takes a swim in that lake you always walk by. In fact, just one dose of monthly flea treatment for a large dog is enough to kill 25 million bees!4
Moreover, the presence of these chemicals in our homes and freshwater means that we are also constantly exposed to them at low levels, which research has suggested can make us more prone to cardiovascular diseases and other medical conditions.5,6
These findings remind us that even our smallest acts of care, like hanging out pet fur for nesting birds, can ripple through ecosystems with unintended consequences. Taking the time to rethink these habits is a simple but powerful step toward living in true harmony with nature.
HOW CAN WE FIND ANOTHER WAY?
What can we do to stop fipronil and imidacloprid from harming our wildlife, our pets, and ourselves? Avoid letting your pets play in waterways or washing them in the days following flea treatment, and increase the intervals between medications, especially during the low-risk winter season. Alternative ways to deliver the treatment are also an option, with both oral and injectable flea treatments already available, and less likely to leach into the environment. You can also try alternative flea treatments, including home remedies and herbal spray (please consult a vet before trying). Of course, the most important step, and one we can all take part in, is to press for a ban to rid this country of fipronil and imidacloprid once and for all.
Article written by Giulia Checchi
Primary paper:
Tassin de Montaigu, C. et al. (2025) ‘High prevalence of veterinary drugs in bird’s nests’, Science of The Total Environment, 964, p. 178439. doi:10.1016/j.scitotenv.2025.178439.
Other references:
- Fisher J., and Hinde, R.A. ‘The opening of milk bottles by birds’. (1949). Available at: https://www.cabidigitallibrary.org/doi/full/10.5555/19520402565 (Accessed: 08 May 2025). doi:
- Rigal, S. et al. (2023) ‘Farmland practices are driving bird population decline across Europe’, Proceedings of the National Academy of Sciences, 120(21). doi:10.1073/pnas.2216573120.
- Lóbez, I.M. (2020) ‘Lethality of imidacloprid and fipronil on apis mellifera: A retrospective analysis on the French case’, Journal of Agricultural Science and Technology A, 10(3). doi:10.17265/2161-6256/2020.03.002.
- Dunning, H. (2023) ‘Toxic pet flea and tick treatments are polluting UK freshwaters’, Imperial News: Imperial College London. Available at: https://www.imperial.ac.uk/news/243875/toxic-flea-tick-treatments-polluting-uk/ (Accessed: 08 May 2025).
- Perkins, R. A. (2024). ‘The environmental fate of fipronil and imidacloprid used in pet parasiticides’. Doctoral dissertation, University of Sussex.
- Gibbons, D., Morrissey, C. and Mineau, P. (2014) ‘A review of the direct and indirect effects of neonicotinoids and fipronil on vertebrate wildlife’, Environmental Science and Pollution Research, 22(1), pp. 103–118. doi:10.1007/s11356-014-3180-5.
All images taken from Canva
