Which bed bug treatment actually works?

On an ordinary pest, effectiveness is judged in days. On Cimex lectularius, that criterion is worthless, for a reason of physiology.

An adult bed bug feeds on blood every five to ten nights when it gets the chance. When it does not, it drops into a waiting state and survives several months without a meal, longer still at cool temperatures. A home left empty to "starve out" an infestation does not starve it: it puts it on pause.

Three consequences, and they govern everything else in this article:

• Silence is not a result. Two weeks without a bite after a spray usually means the surviving individuals have moved away from the bed, not that they have gone.
• A treatment is judged at six weeks, never at forty-eight hours.
• The real indicator is a check of the evidence — black specks, cast skins, live insects at the inspection points — not how the person sleeping there feels.

Finding that evidence follows a set order — seams, bed base corners, the back of the headboard, skirting boards — detailed further down, in the section on the final check.

The timetable of a treatment is not commercial, it is biological. Here are the figures that set it, at the temperatures of a Marrakech home.

• Egg laying. A fertilised female lays a few eggs a day, glued one by one into a crevice — a seam, a split in a bed base, the back of a skirting board. The eggs are white, around a millimetre across, and strongly stuck down: they do not fall out when you shake the mattress.
• Incubation. Roughly six to ten days at twenty-five to thirty degrees, longer when it is cooler. The shell of the egg is the key point of this whole article: it does not let contact insecticides through.
• The five nymphal stages. Each moult requires a blood meal first. The full passage from egg to adult takes something like five to seven weeks at moderate temperatures, and shortens sharply in a warm bedroom.

Hence the interval for the second visit: fourteen to twenty-one days. Late enough for the eggs present on day one to have hatched, early enough that the nymphs from that hatch have not reached breeding age. Treating at three days achieves nothing; treating at six weeks means starting again.

This two-visit principle is not specific to bed bugs: it applies to every species whose eggs are protected, such as the German cockroach and its ootheca.

This is the point supermarket shelves never mention, and it has changed the picture over the last fifteen years or so.

Pyrethroids were the reference family against bed bugs. Their heavy, repeated use, all over the world, has selected populations carrying two resistance mechanisms: a modification of the nerve target site that makes the molecule inoperative, and an overproduction of detoxification enzymes that breaks it down before it can act. A bug from a resistant line walks through a dose that would have killed its ancestors.

On top of that sits a behavioural property few people know about: many of these products are repellent at low dose.

In practice, a domestic spray kills only some of the insects it reaches and drives the rest into partition walls, electrical conduits, the skirting boards of the next room, sometimes the flat next door. The infested area grows, and the professional treatment that follows will be longer and more expensive.

What to take from it:

• a spray bought off the shelf before the call is almost always a worsening, never a saving of time;
• a professional who only sprays a single family of molecules reproduces the problem;
• the answer to resistance is not "a stronger product", it is combining different modes of action, at least one of them non-chemical.

That is the first question to put to any contractor: which modes of action they combine, and why. An answer that boils down to a product name is not an answer.

Against the shell of the egg, contact chemistry fails by design. Temperature gets round nothing: it goes straight through.

The principle is thermal, not chemical. The insect's proteins denature beyond a threshold of a few tens of degrees, and that threshold holds for every stage — egg, nymph, adult.

What matters is not the temperature displayed on a machine, it is the temperature reached at the heart of the hiding place and how long it is held there. A mattress heated at the surface for ten minutes has not been treated: the middle of the padding has not moved.

The limits, said plainly:

• anything heat-sensitive leaves the room first: electronics, candles, aerosols, vinyl records, adhesives, thin plastics, some varnishes and old timber;
• heat leaves no residual effect whatsoever. It settles the moment, not the following week — hence the need for a perimeter treatment that does last;
• it assumes a volume you can control. A bedroom, a mattress, a batch of fabrics: yes. A whole flat open onto a stairwell: no.

That is why thermal and residual approaches are not rivals. The first empties the stock of eggs, the second covers the emergence. Either one without the other leaves a gap.

These are the two most underrated steps of the treatment, and the only ones the occupant can carry out without making anything worse — provided the protocol is followed.

Vacuuming. It removes part of the population straight away: adults, nymphs, cast skins, droppings, and a fraction of the eggs when the nozzle passes close enough to the seam. It has a further benefit that is usually ignored: it abrades the surface wax of the cuticle, which leaves the insect more vulnerable to whatever follows. Three rules:

1. flat nozzle, no rotating brush, passed slowly along seams, piping, folds and grooves;
2. after each zone, the vacuum bag leaves the house immediately, sealed, inside a second bag;
3. never rinse a bagless cylinder in the kitchen sink.

Sealing into bags. Everything sorted, washed or treated has to be isolated in closed plastic bags, marked, and stored outside the bedroom. An open bag left beside the bed is one more harbourage. A sealed plastic bag is not a treatment method — a bug survives in one for a long time — but it is a transport barrier, and transport is the number one mechanism of spread.

Upholstered divan bases and padded headboards call for a treatment of their own, left to the specialist. The mattress itself can be deep-cleaned once the infestation is over: cleaning a mattress at home removes stains and odours, it does not replace a treatment.

Fabrics are dealt with at home, and a good part of the result is decided there. Three routes, three different effects.

• A machine wash at sixty degrees. That is the useful benchmark: above roughly fifty degrees held for long enough, neither the mobile stages nor the eggs survive. A wash at thirty degrees cleans the fabric and does nothing else.
• The tumble dryer on a hot cycle. Often more effective than the machine, because the heat there is dry and sustained. A full hot cycle treats what cannot take sixty degrees in water — a jumper, a throw, a lined curtain.
• Cold. A domestic freezer works, but slowly: it takes several consecutive days at a low, stable temperature to reach the core of an object. Six hours does nothing. This route is for small unwashable items: books, picture frames, shoes.

Two classic mistakes: taking treated items out and putting them back on a bed that has not been treated yet, which recontaminates everything; and piling the bedroom's dirty washing in the corridor before washing it. Treated items go back into a sealed bag and only return to the bedroom after the intervention.

All of this is done by the occupant, in their own home. Whatever goes neither into the machine nor the dryer — padded seating, heavy bedspreads — is for the specialist treating the home. Only after their last visit can sofas, mattresses and rugs be given on-site upholstery cleaning: that is hygiene, not a treatment.

These five situations come round on a loop, and not one of them is a product problem.

1. The second visit never happened. Either it was not in the quotation, or the occupant cancelled it because "things are better". That is cause number one, a very long way ahead of the rest.
2. A room was left out of the scope to bring the quotation down. The sofa in the living room, the child's bedroom, the study with a sofa bed. A bed bug does not recognise the boundaries of a quotation.
3. An untreated piece of furniture or fabric is brought back in between the two visits: a box stored at a relative's, a suitcase fetched up from the cellar, a spare mattress.
4. The treated points have been cleaned. Washing down the skirting boards removes the residual effect exactly where it was supposed to last three weeks.
5. The flat next door is infested and untreated. In a dense building, service ducts and pipe runs are corridors. Treating alone means repeating the operation every six months — hence the value of a collective approach, organised with the managing agent across the whole building.

One last cause, rarer but expensive: misidentification. Fleas, booklice, storage mites and skin reactions of non-parasitic origin produce similar pictures. A serious professional does not treat a species they have not seen.

A treatment closes on a check, not on an impression. Here is what a professional looks at during the second visit, and what you can look at yourself.

• The inspection points identified at the first visit — seams, bed base corners, the back of the headboard, the skirting boards behind the bed — are re-examined under a raking light at the second visit. The aim is to find live insects, not old traces.
• Dry black marks stay visible long after an infestation has ended. On their own they prove nothing: they are past droppings. That is why a serious contractor removes or marks them at the first visit, so it is clear whether new ones appear.
• Monitoring traps placed under the bed legs and behind the headboard give a comparable measure from one week to the next. Zero catches over several consecutive weeks is the only solid signal.
• Time. A focus only counts as extinguished after an observation period covering at least one full development cycle, that is several weeks after the second visit.

What no honest professional issues: a certificate of absence of bed bugs. Nobody can prove an absence in an occupied home. What you should obtain is a dated intervention report, with the area treated, the findings and the recommendations — a different document, and the only honest one. The particular case of premises open to the public is covered separately.