Can a Hot Car Kill Bed Bugs?

No, not reliably, and not in Toronto for most of the year. Killing bed bugs by leaving a car in the sun is repeated everywhere as advice because the two numbers involved look compatible. Bed bugs die at around 45 degrees. A parked car on a clear summer day can reach 68. Case closed, apparently.

The problem is that those two numbers describe different places. The 45 degrees is measured at the insect. The 68 is measured in the cabin air. Nobody has published a measurement of the temperature inside a seat seam, under a seat or in a foam cushion core, which is where the insects actually are, and that gap is the whole argument.

This part is well established. In work published in PLOS ONE, bed bugs held at 45 degrees showed a median lethal time of 14.3 minutes and 99 per cent mortality at 23.2 minutes. A 22 minute exposure produced complete mortality of adults and of fourth and fifth instar nymphs. Practical field treatment generally targets 50 degrees or higher with sustained exposure, because a professional heat treatment has to account for the same penetration problem a car does.

The same research tried to breed heat resistance into a colony and could not. The selected line died out before the eighth generation. So the threshold is stable and it is not going to shift on you.

You will see a figure of 90 minutes quoted in a lot of the online advice, including in the answers Google itself is currently surfacing. That number is more conservative than the published research, and it comes from heat treatment equipment vendors rather than from the entomology. Either way it makes the same point: this is a sustained exposure at a specific temperature, not a hot afternoon.

Also well measured, and higher than most people expect. Research published in the International Journal of Biometeorology recorded maximum cabin temperatures between 41 and 76 degrees, averaging around 68 on clear summer days and 61 on clear spring days. Cloud cover took roughly 10 degrees off the top.

Work published in Pediatrics measured how fast it happens. The cabin rises about 3.2 degrees Fahrenheit every five minutes, 80 per cent of the total rise occurs within the first half hour, and the average peak sits 41 degrees Fahrenheit above the outside air. That study also tested the thing everyone assumes helps, and found that cracking the windows made no significant difference.

So on a clear July afternoon in Toronto, cabin air in a closed car is comfortably past the lethal threshold within an hour. If the insects were sitting on the dashboard, this would work.

They are not on the dashboard. Bed bugs are flat, they avoid light, and they sit in exactly the places heat reaches last. Inside a stitched seat seam. Under the seat, shaded by the seat itself. In the foam core of a cushion, behind several centimetres of upholstery. In the seatbelt buckle housing. In the trunk, which is separated from the cabin entirely and gets a fraction of the direct sun the windscreen delivers.

Every one of those is an insulated pocket, and every one of them lags behind cabin air. How far behind is the question that decides whether any of this works, and we have not been able to find a single published measurement of it. Not in the entomology literature, not in the automotive literature, and not in the pest control industry protocols, which describe the harbourage points confidently and cite nothing.

That is an unusual thing to be able to say about advice this widely repeated. The claim that a hot car kills bed bugs rests on an assumption that the inside of a seat reaches the same temperature as the air above it, and that assumption has never been tested.

It is also the reason professional heat treatment is expensive and slow. A company treating a room does not heat the air to 45 degrees and leave. They run it higher for hours, with fans moving air into voids, and they place sensors at the harbourage points to confirm the temperature reached them. A car in a parking lot has none of that.

Those cabin figures come from clear summer days. Toronto gets a narrow window where this is even arguable. A cloudy August afternoon takes about ten degrees off, which moves the cabin from comfortably lethal to marginal before you even ask about the seat foam. From roughly October through May the question does not arise.

There is also a practical problem with the advice that nobody mentions. To do this you have to leave the car closed and unused through the hottest part of a day, repeatedly, without knowing whether it is working, while the thing you are trying to fix may be reproducing. Bed bug eggs hatch in five to seven days at 25 degrees. A few failed afternoons is enough time for the population to grow rather than shrink.

The winter version of this advice is more confident and less supported. Bed bugs held at zero degrees largely survived regardless of how long it went on. At minus five for three weeks, mortality reached 54 per cent in nymphs and 79 per cent in adults, which means a substantial proportion were still alive after three weeks of hard cold. Complete mortality took roughly three weeks at minus seven to minus 10 degrees held constant. At minus 10 for a single week, nymph mortality stayed under 20 per cent.

Now the detail that matters for a vehicle. In the same research, fluctuating temperatures produced lower mortality than constant ones. Cold kills through sustained exposure, and anything that lets the insect warm up periodically resets the clock.

A car parked outside through a Toronto winter is the definition of a fluctuating environment. It warms when you drive it, warms again when the sun hits the glass, and drops overnight. That is close to the worst case for cold kill rather than the best one, which is the opposite of what the advice assumes.

Very little, and it is worth saying so given how confidently this gets discussed. Ask whether bed bugs live in cars and you will get a confident yes from most of the internet, but we have not found a peer reviewed study of bed bug survival, establishment or population growth in passenger vehicles. The guidance that exists comes from pest control industry protocols that describe harbourage points without citing research behind them.

What is established comes from work on how infestations spread generally. Bed bugs move passively, carried on people and their belongings, rather than travelling any distance under their own power. In one documented case a single frequent traveller had 551 insects trapped in their apartment over four weeks without being aware of any of them. Somebody in that situation getting into a car is the mechanism, and it does not require anything unusual.

Whether a vehicle then sustains a population the way a bedroom does is genuinely open. A car has no sleeping occupant to feed on for hours each night, which argues against it. Adults survive months without a blood meal, with controlled starvation studies recording survival past 140 days, which argues that a vehicle can carry them a long way regardless of whether they are breeding.

The honest position is that a car is more likely to be a vector than a habitat, and that neither claim has been measured properly.

Find out whether anything is actually there before you spend a summer on a method that may do nothing. That is not a sales line, it is the order the problem has to be solved in. A vehicle is a small sealed space, which means a canine sweep takes ten to twenty minutes with the doors and trunk open, and you get an answer that afternoon rather than a theory you cannot test.

If something is found, the useful output is the location, because a pest control operator can treat a named seam or buckle housing properly rather than fogging an interior and hoping. If nothing is found, you have stopped paying attention to a problem you do not have, which for a rideshare or taxi driver is worth more than the inspection costs in a single day of not taking the car off the road.

The one thing that is worth doing regardless, and costs nothing, is to stop the passive transfer. Keep bags out of the cabin and in the trunk where you can. Vacuum seams rather than surfaces, and empty the canister outside the vehicle. Neither of those solves an infestation, and neither is claimed to.