Pesticides and Wildlife: Rodenticides, Insecticides, and Secondary Poisoning

Agricultural and domestic pesticide use causes massive but largely hidden mortality in wildlife populations. Understanding the mechanisms and scale of harm is the first step toward reform.

Key Facts

Rodenticide poisoning is the leading cause of death in barn owls in many regions — a 2020 study found over 90% of UK barn owls tested had rodenticide residues in their livers
Second-generation anticoagulant rodenticides (SGARs) accumulate in predator tissues through bioaccumulation, poisoning raptors, foxes, and mustelids that eat poisoned rodents
Neonicotinoid insecticides are systemic — absorbed by entire plant tissue — meaning pollen and nectar contain levels lethal or sub-lethal to bees and other pollinators
The EU banned outdoor use of three key neonicotinoids (imidacloprid, clothianidin, thiamethoxam) in 2018, though emergency exemptions have continued in some countries
Glyphosate affects habitat quality for wildlife by reducing the plant diversity that supports insect communities, with cascading effects on higher trophic levels
Insecticide drift from agricultural spraying kills non-target invertebrates including beneficial insects, earthworms, and aquatic invertebrates in field margins
UK insect biomass has declined by 60% in 20 years — pesticide use is identified as a major contributor alongside habitat loss and climate change

Welfare Considerations

The welfare impacts of pesticide exposure in wildlife are both acute and chronic. Rodenticide poisoning causes slow internal haemorrhage — a painful death that may take days. Sub-lethal rodenticide exposure impairs immune function, reproduction, and behaviour in predators, reducing their welfare and survival without an obvious acute poisoning event. For invertebrates, neonicotinoid exposure causes disorientation, navigation failure, and reproductive impairment in bees — welfare harms that are real even if the moral status of insect suffering remains debated. The systemic, landscape-scale nature of pesticide impacts means that even wildlife populations far from treated fields are affected through food web contamination and habitat degradation. This is a welfare crisis operating at a scale that dwarfs individual animal incidents.

What You Can Do

Avoid using second-generation anticoagulant rodenticides domestically — use snap traps, live traps, or exclusion methods instead
Never use slug pellets containing metaldehyde or methiocarb — they are toxic to birds, hedgehogs, and other wildlife; use ferric phosphate alternatives
Advocate for mandatory rotation of rodenticide applications and use of kill-based evidence before SGAR use on farms
Support the Campaign for Responsible Rodenticide Use (CRRU) standards and advocate for their adoption by farmers and pest controllers
Plant pollinator gardens free from any pesticide treatment — even organic-approved pesticides can harm beneficial insects
Advocate for your local authority to adopt pesticide-free parks and verge management policies
Support neonicotinoid bans and oppose emergency exemptions — the scientific evidence for pollinator harm is robust and consistent