Robot mowers, hedgehogs and wildlife: safety and schedules

Short answer: robot mowers can hurt hedgehogs, mostly at night. Run yours in daylight only, check the lawn before the first run of the day, and don't treat any obstacle detection as a guarantee. That single change to the schedule is the most effective thing an owner can do.

Hedgehogs have declined sharply in Britain and are a species of conservation concern, so this isn't a niche worry. The good news is that a robot mower's schedule is entirely under your control, and a lawn cut little and often in daylight can be good for wildlife.

Why hedgehogs are at risk

Three habits make hedgehogs vulnerable to robot mowers:

• They're nocturnal. Hedgehogs forage at night, often on lawns, which are good hunting grounds for worms and beetles. Robot mowers are often scheduled to run overnight precisely because nobody is using the garden.
• They curl up instead of running. A hedgehog's defence is to roll into a ball and stay put. That works against a fox; it doesn't work against a machine that keeps coming.
• They're small and low. A curled-up hedgehog is roughly the size of a grapefruit, brown, and sits in long grass or at the lawn edge, which makes it hard for sensors to recognise.

Other wildlife, including frogs, toads, slow-worms and young birds, faces similar risks, especially near ponds and long-grass borders.

What the research found

The most useful work on this comes from Dr Sophie Lund Rasmussen, known as "Dr Hedgehog", at Aalborg University and the University of Oxford's Wildlife Conservation Research Unit. Her team tested robot mowers against hedgehog carcasses (from animals that had already died in rescue centres) to see how different designs behaved on contact. Hedgehog Street's summary of the research and the University of Oxford's announcement of a hedgehog safety test set out the main points:

• Robot mowers can injure hedgehogs, and the severity varied widely between models.
• Some design features, such as pivoting blades, front-wheel drive and skid plates, were linked with less harm.
• The mowers tested needed physical contact to detect a hedgehog; none reliably spotted one in advance.

The researchers have been working towards a standard test so that mowers could one day be certified as hedgehog-friendly. At the time of writing we're not aware of a certification scheme that UK buyers can use to compare models, so be sceptical of any product described as "hedgehog-safe" without evidence behind it.

These studies tested the mowers available at the time. Many newer mowers use cameras, LiDAR or both, and some may detect small animals better. But no manufacturer we know of publishes independent hedgehog test results, so the safe assumption is that any mower can cause harm.

Daytime-only schedules

Hedgehog Street, the campaign run by the British Hedgehog Preservation Society and People's Trust for Endangered Species, advises running robot mowers only in the day and checking the lawn for wildlife before you start. How to do that in practice:

• Start after sunrise and finish before dusk. Leave an hour or so either side. In a UK summer that still leaves a long mowing window; in spring and autumn it's shorter, but the grass grows more slowly too.
• Revisit the schedule as the seasons change. A 7pm finish is fine in June but falls after dark in October. Some apps let you set seasonal schedules, but many don't adjust automatically.
• Turn off night mowing features. Some mowers offer a quiet or night mode. Leave it off.
• Don't use "mow when rain stops" at night. Rain delay features can shift a session into the evening. Check how your mower handles a missed session.
• Check before the first run. A quick look along borders, under hedges and in long grass takes a minute. Hedgehogs sometimes sleep in compost heaps and under sheds by day, and occasionally in long grass at the lawn edge.

A daylight-only schedule is also friendlier to neighbours, and most mowers can still cover their rated area in daytime hours. If a mower can only keep up with your lawn by running all night, it's too small for the garden.

What obstacle detection can and can't do

Robot mowers detect obstacles in several ways, and it helps to know what each one is good for:

• Bump sensors detect contact. Every mower has them, and they're the basic safety system on wired models such as Flymo's EasiLife range, which Flymo lists with collision, lift and tilt sensors. Contact is exactly what you're trying to avoid with a hedgehog.
• Ultrasonic sensors can spot larger objects ahead, but may miss small, low, soft ones.
• Cameras and AI vision can recognise objects. Some manufacturers make specific claims: eufy says the C15's vision system detects small animals and pets. Husqvarna's V-series NERA models, such as the Automower 430V NERA, add an AI camera that Husqvarna says has infrared for night use.
• LiDAR measures shapes and distances and is good at walls, trees and furniture. Small, low objects in grass are harder.

These are manufacturer claims, and they generally refer to obstacles such as toys, shoes and pets. None of them is an independent assessment of hedgehog safety. A mower that avoids a football in daylight hasn't been shown to avoid a curled-up hedgehog in the dark. Treat detection as a second line of defence behind a daylight schedule, not a reason to mow at night.

Physical design matters too. The research above found pivoting blades were associated with less harm than rigid ones. Most robot mowers use small pivoting razor blades, but not all; our blade guide explains the types.

Making the lawn safer for wildlife

A few small changes help hedgehogs and other wildlife beyond the mowing schedule:

• Leave a wild strip. A border of longer grass, excluded from mowing as a no-go zone, gives insects and the animals that eat them somewhere to live. Keep an eye on its edge, which is where hedgehogs tend to shelter.
• Keep the mower off pond edges. Frogs and toads gather there, especially in spring. A no-go zone or a wire island round the pond does the job.
• Create a hedgehog highway. A gap of about 13 cm by 13 cm at the bottom of a fence lets hedgehogs move between gardens. Hedgehog Street explains how to make one. It doesn't interfere with a robot mower, but make sure your boundary doesn't route the mower through it.
• Check before strimming too. Strimmers and brush cutters injure hedgehogs in long grass and hedge bottoms, often more severely than mowers. The same check-first advice applies.
• Store the mower in its dock, not on the lawn. A mower left stranded on the lawn overnight is one more obstacle, and if it restarts after dark the risk returns.

If you find an injured hedgehog

If a hedgehog has been hurt, act quickly. Pick it up with thick gardening gloves, put it in a high-sided box lined with a towel and keep it somewhere quiet and warm. Don't give it milk. Then call a local hedgehog rescue or the British Hedgehog Preservation Society, which runs a helpline and keeps a list of rehabilitators across the UK. A hedgehog out in the daytime is also often unwell and worth reporting.

Choosing a mower with wildlife in mind

Wildlife safety isn't a spec you can sort by yet, but you can make sensible choices:

• Pick a mower with enough rated area to finish your lawn in daylight hours with room to spare.
• Make sure the app lets you set a precise, easily changed schedule, including seasonal changes.
• Prefer pivoting blades and a design that keeps the blades well inside the body.
• Look for camera or LiDAR obstacle detection as a bonus, not a replacement for the schedule.
• If a manufacturer claims its mower is safe for hedgehogs, look for published, independent evidence.

For more on how the different sensors work, see how robot lawn mowers work and RTK vs vision vs LiDAR.