Why Are Bed Bugs Hard to Treat With Shop Sprays?

1. It Goes Where They Are Not

The biggest reason and the least obvious. A bed bug sits in a gap that touches it on both sides — inside a seam, in a countersunk screw hole, behind a headboard, in the fold of a stapled fabric edge.

An aerosol goes where it can be aimed, which is open surfaces: the top of a mattress, the face of a frame, the floor. Those are precisely the surfaces they do not sit on.

So the product arrives everywhere except the twenty or so places that matter, and the fact that it kills bed bugs on contact is not much use when it does not reach any.

2. Contact Kill Versus Residual Effect

Most household aerosols are essentially contact products: they work on an insect they land on. That is fine for a wasp on a windowsill and close to useless for an animal that spends ninety-nine per cent of its life out of sight.

What a bed bug treatment needs is something that stays where it is put and is encountered by insects moving through a harbourage over the following days — which is a different kind of product used in a different way, into the gaps rather than onto the surfaces.

3. Nothing Reaches the Eggs

Eggs are cemented into the tightest part of a harbourage with a shell around them, and they hatch on their own schedule — a week or two at room temperature.

That produces the pattern everybody recognises: a household sprays, things improve markedly for a fortnight, and then it comes back. That is not the product wearing off. It is the generation that was never affected arriving on time.

4. It Disperses Them

The one that actively costs you. Disturbing a harbourage — spraying into it, or repeatedly poking about in it — drives insects out of it and into the next available gap, which is further from the bed and sometimes in the next room.

A room that has been sprayed repeatedly over months is often more widely spread than an equivalent room left alone, and it is harder and more expensive to deal with as a result.

What About Resistance?

Worth mentioning and worth not overstating. Resistance to some insecticide groups is documented in bed bug populations internationally, and it is one of the reasons this is a harder pest than it was fifty years ago.

It is not, though, the main reason a household aerosol fails in a bedroom. The first three reasons on this page would defeat a perfectly effective product used the same way, and they are the ones that apply in almost every case.

The Other Shop Products

• Foggers and bombs. Fill a room with a fine mist that settles on open surfaces. Same problem as the aerosol, with more dispersal and more disturbance
• Powders. Some have a genuine place in professional use, applied into specific voids. Scattered over a carpet by a householder they do very little and create a mess that has to be cleared before anything else can happen
• Plug-in repellers. No
• Sprays sold as natural or plant-based. Mostly contact products with the same limitation, and the same fortnight of apparent success

Maidenhead: If You Have Already Used Something

Most households have and it is not a disaster. What it means is worth saying plainly when you call.

• The population may be more widely spread than the evidence suggests
• Residue on surfaces can affect what is usable on them afterwards
• The evidence may have been disturbed, so the picture is less readable
• The room may need a wider inspection than it otherwise would

All four are manageable when they are known about. None of them is manageable when they are discovered halfway through a visit.