Robot grass cutters are mowing down wildlife

Robot lawn mowers are injuring hundreds of protected hedgehogs in Germany, and nearly half of those sliced by the machines are killed or die as a result of their wounds.

Autonomous mowers, first developed in the 1990s, are now readily available throughout the world and retail between $1200 and tens of thousands of dollars. Most are unable to detect hedgehogs without physically touching them.

Researchers from Germany’s Leibniz Institute for Zoo and Wildlife Research collected data on hedgehog injuries caused by robot mowers over 16 months, finding 370 animals were injured, 175 of which did not survive. More than 10% of injured hedgehogs were nestlings or juveniles.

West European hedgehogs (Erinaceus europaeus) are small, solitary and nocturnal animals, attracted to household gardens. The species is in long-term decline across Europe due to habitat loss, declining food sources, human activities and climate-related effects. 

In 2024, the hedgehog was named Wild Animal of the Year by the German Wildlife Foundation.

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Robot mower cutting high grass / Fokusiert / iStock / Getty Images Plus

The study follows a significant increase in reports of cutting injuries by garden equipment at wildlife care centres, alongside a rapidly expanding global market for robot lawn mowers. 

Robot mowers are quieter, work unattended, and often run at night – a time when hedgehogs are active. 

Hedgehog injuries often go unnoticed due to the autonomous nature of the machines and lack of supervision. The study shows at least 60% of injured animals were found more than 12 hours after the accident.

“There is not a single day of the week on which hedgehogs suffer cuts particularly rarely or particularly often. This is a clear indication that robotic lawn mowers – whose sales figures are increasing year on year – are often the cause of these injuries, as these devices are the only ones that can legally be used on a Sunday,” says Dr Anne Berger who led the study.

Igel mit schnittverletzungen hedgehog with cut injuries photo editha schneider
Hedgehog with cut injuries found in a German private garden / Credit: Editha Schneider

A second study explains the threat, revealing 19 models of commercially available robot mowers are unable to detect hedgehogs without physically touching them.

Researchers tested robot mowers on hedgehog carcasses, positioned in 6 common poses based on a third study. Damage was recorded on a scale from 0: no physical contact, through to level 4: “the robotic lawn mower fails to detect the presence of the hedgehog and continues to drive across it”.

In multiple tests performed across the 19 models, there was only one incidence of damage category 0, a result that could not be replicated by repeating the test. Every other instance included contact with the hedgehog. The majority of mowers recorded level 4 injuries on some tests. 

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Smaller hedgehogs are more at risk / iStock / Samoilov / Getty Images Plus

The position of the hedgehog did not significantly affect the outcome. Larger hedgehogs were less likely to be injured.

The tests were carried out according to standard product testing protocols with the aim of designing a hedgehog safety test for the garden appliances. The researchers propose a standardised safety test, and are working on designing a hedgehog ‘crash test dummy’.

The third study explores common reactions of 50 live hedgehogs to a disarmed robotic lawn mower, identifying 7 responses. The most frequent response (43%) was to stand “completely still, as if they are in a frozen state, often in an upright position with the snout pointing inwards”. In only 15% of cases, the hedgehog ran away.

The three studies on robot mowers and hedgehogs are published in Animals.

Hedgehog crash test dummy
A 3D printed prototype hedgehog crash test dummy developed by the researchers / Credit: Sophie Lund Rasmussen

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