No. Plug-in ultrasonic repellers have not been shown to clear mice, rats or cockroaches from a house. Rodents get used to the sound within a short time, and the sound cannot reach the wall cavities, roof voids and cracks where pests actually live. In controlled trials, cockroaches, ants and bed bugs showed no response to the devices at all.
What do these devices claim to do?
Most units plug into a power point and give off a high-pitched sound above the range of human hearing. Some also claim to give off electromagnetic pulses. The idea is that the noise irritates rats, mice and insects until they leave the building.
Australia's consumer regulator has tested those claims before. In 2004 the Australian Competition and Consumer Commission (ACCC) said a group of companies selling plug-in pest devices had advertised that they created an "ultrasonic barrier", drove pests out of a home and disrupted nests inside walls. More than 240,000 units had been supplied since 1997. The ACCC said there was little evidence the devices worked to the extent claimed, and the companies gave court-enforceable undertakings to stop the claims and offer refunds.
What happens when rats and mice hear the sound?
They adjust to it. A rodent control manual written for Australian poultry farms through AgriFutures Australia says rats and mice quickly get used to ultrasonic noise, a process called habituation. A University of Arizona Cooperative Extension review of the research describes the same pattern: rats and mice showed a mild dislike of the sound that faded over time, especially once they found food near the device.
The AgriFutures manual also points out that ultrasonic waves cannot pass through solid objects or travel around corners, and that commercial units only cover a short distance. That matters inside a house. The Victorian Department of Health rodent pest control page says roof rats are good climbers that nest in buildings and roof voids, and that house mice live inside buildings and gnaw holes up to 20 millimetres wide in walls, partitions and floors. A unit plugged in at skirting level sends sound across one room. It does nothing for a nest behind the plasterboard or above the ceiling.
Grays Point sits beside the Royal National Park, and wildlife such as possums and sugar gliders lives in the suburb. A family there who plugged a repeller into the hallway and still hear scratching above the bedrooms every night has an animal in the roof the device never reached. Booking rat and mouse control in Grays Point lets a technician confirm whether it is a rat or native wildlife before anything is placed. The Victorian health page lists lockable bait stations as one way to keep baits away from children, pets and wildlife.
Do they keep cockroaches away?
No. The Arizona review describes a study that tested nine devices on German cockroaches. Just as many cockroaches walked into rooms with the sound switched on as into rooms without it. A later trial used a device built to produce a wide range of ultrasonic frequencies and still found no response from German cockroaches.
The Victorian health page on cockroaches says German cockroaches are found under sinks, in and under cupboards and drawers, and around appliances such as refrigerators, and that they hide in cracks and crevices during the day. That is often exactly where a repeller gets plugged in, a few centimetres from the cockroaches it is meant to drive out.
Como sits on the southern bank of the Georges River. A Como kitchen where cockroaches still run out from behind the fridge at night, with a repeller glowing in the power point beside it, needs cockroach control in Como aimed at the cracks, cupboard hinges and appliance gaps where they shelter during the day.
What about ants and bed bugs?
The same review reports that three devices tested on three ant species failed to repel them in field and laboratory trials. One device seemed to deter ants briefly in the laboratory before it stopped having any effect. In a test of four devices against bed bugs, roughly equal numbers of bed bugs settled near the devices as on the side with no sound.
Taren Point is a small waterfront suburb on the Georges River near the mouth of Botany Bay. If ant trails keep crossing a Taren Point benchtop while a repeller hums in the corner, the colony is nesting somewhere the sound never travels. Ant control in Taren Point should start by tracing where the trail enters the house.
Why is waiting on a repeller a problem?
Because the pests keep breeding while you wait. The Victorian health guidance says house mice reach breeding age at about six weeks and a female can have 6 to 10 litters a year. Roof rats have 4 to 5 litters a year, with 6 to 8 pups in each. A month of trusting a device that is not working gives a small problem time to become a much larger one.
Rodents also gnaw through a wide range of materials and spoil food with their droppings, according to the same guidance. The longer they stay, the more of the pantry and stored boxes they reach.
Miranda is the Shire's main retail and commercial centre, with shops on both sides of the railway line. Someone in a Miranda unit near the shops who finds fresh droppings in the pantry each morning, despite two repellers in the kitchen, should book quick mouse and rat control in Miranda before the mice settle further into the wall cavities.
Before you book
Write down what you have seen and heard: droppings and their size, gnaw marks, scratching and the time of night, or cockroaches and where they run when the light goes on. Note where any repellers are plugged in and how long they have been running, because that tells the technician how long the pests have been left to breed undisturbed. Send those details to our Sutherland Shire pest control team: call Sutherland Shire Pest Control Pro on 02 8360 3033 or email [email protected].