One monthly imidacloprid cat or dog flea treatment could kill up to 25 million bees

The Times reports today, March 21, 2023, that a popular cat, dog, rabbit flea treatment containing imidacloprid could kill millions of bees when the toxin is washed into waterways according to researchers at Imperial College London, UK. The pesticide is used in 138 pet treatment sold in the UK alone. God only knows how many products there are worldwide. It is FDA approved in America but clearly approval of insecticide in a flea treatment does not include assessing its damaging environmental impact to pollinating bees which are vital to ecosystems.

Imidacloprid in pet flea treatments can and does kill millions of bees

Imidacloprid in pet flea treatments can and does kill millions of bees. Infographic by MikeB at PoC.

For example, they state that “one monthly flea treatment for a large dog contains enough imidacloprid to kill 25 million bees. In aquatic ecosystems, insect larvae are particularly at risk, such as mayflies and dragonflies.”

American brands

My research reveals that imidacloprid is a common insecticide in different brands of flea treatment in various countries. For example, VCA hospitals in America answer the question: “What flea treatments contain imidacloprid?” The answer: brand names include: K9 Advantix®, Advantage II®, Advantage Multi®, Seresto®, Advocate®). At labeled doses, its use in cats, dogs, and ferrets is FDA – approved, the add.

Some brands actually use the name of the chemical to name the flea treatment as seen in the infographic.

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The researchers reviewed 160 scientific papers and the impact of this toxin on aquatic ecosystems. Mayflies and dragonflies are important food for bats, birds and fish.


Garry Woodward, an ecologist said that “if you start pulling those species out [it is] like playing Jenga with the food web”. What is saying is that if you pull out a central part of food chains you break the food chain network. There is an enormous knock-on effect.

Huge increase in use

In the decade up to 2019, sales of products containing this toxin rose by 152% in veterinary clinics in the UK. In 2019 2,500 kg of the chemical was sold for veterinary use compared to 4,000 kg in 2014 for agricultural and veterinary use combined.

Entering waterways

The toxin enters waterways when owners flush some of the product as waste down the lavatory as well as washing their hands after applying it to their pet.

Even if the amount of toxin is so small as to not kill invertebrates, they slow down their growth and reproduction rates. This serves to deprive fish and bats of food.

In the UK, the Environment Agency assessed 20 rivers which showed that imidacloprid was present in two thirds of the samples taken. In 52% of those samples, they decided that the chemical posed a “moderate to high” risk to freshwater species.

A researcher at Imperial, Leon Barron, said that invertebrates “filter out chemical pollution [and] if you’re knocking them out, things get out of whack, and your river starts to decline”.

The European Union banned the sale of imidacloprid for farm use in 2018 when the UK was a member of the EU. But it is sold in large quantities in the European Union and the UK.


Andrew Prentice, a visiting fellow at Imperial, suggested that pet owners should only use flea treatments when their pets had fleas rather than as a preventative.

Better assessment needed

This is yet another example of how chemicals in the home can both be toxic to cats and dogs and other species. In this instance, it is clear that the regulators are only looking at whether this insecticide is dangerous to pets which is surely shortsighted. All flea treatments use pesticides and pesticides are highly toxic to any living creature including humans.

It is ironic that humans wash their hands after putting a spot-on treatment containing this pesticide on their cat because they are fearful that it might injure them. Rather strange, I think. And in doing so they are potentially killing millions of bees. I hope this article helps people to consider using these products less often.


One issue is that vets want to sell the product and push it on clients. Vets are not considering the wider picture and damage the product causes.

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Note: sources for news articles are carefully selected but the news is often not independently verified.

Michael Broad

Hi, I'm a 74-year-old retired solicitor (attorney in the US). Before qualifying I worked in many jobs including professional photography. I love nature, cats and all animals. I am concerned about their welfare. If you want to read more click here.

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