Bed Bug

Cimex lectularius

What does a bed bug look like, stage by stage?

Different enough at each stage that people routinely find one and dismiss it.

The adult is flat, oval and reddish-brown, about the size and color of an apple seed. It has no wings — the small pads on its back are not functional — and it cannot fly or jump. The flatness is the point: unfed, the body is thin enough to slide into a gap you would not think of as a gap. After a blood meal the shape changes completely, becoming swollen, elongated and darker, so a fed insect and an unfed one from the same population look like two different things.

Nymphs pass through a series of stages, each requiring a blood meal before the insect can moult to the next. The earliest are very small and almost translucent — pale straw or nearly colorless until they feed, at which point a dark red mass is visible through the body wall. This is why early infestations get missed. The stage most likely to be present when a problem is new is also the stage hardest to see against a pale sheet.

Eggs are white, roughly the size of a grain of salt, slightly curved, and cemented in place with a sticky secretion. That last detail matters practically: they are glued into cracks, seams and screw holes and cannot be shaken out or brushed away casually.

Cast skins are the shed shells left behind at each moult — pale, papery, translucent, retaining the shape of the insect. They accumulate at harborage and persist long after the population has moved, so finding them tells you a site was used but not necessarily that it is used now.

The characteristic accompanying sign is fecal spotting: digested blood excreted as a dark liquid that dries to a blackish mark. On fabric or paper it bleeds slightly at the edges, which is a good way to distinguish it from a speck of dirt sitting on the surface. On a hard surface it remains a discrete dot. Heavy sites carry a distinctive sweetish, musty odor that experienced inspectors notice before they see anything.

What gets mistaken for a bed bug?

Four things, and each mistake sends the work in a different wrong direction.

Carpet beetle larvae. Small, elongated, distinctly bristly or hairy, often found near carpet edges, in wardrobes, in wool textiles and around windowsills. They shed hairy cast skins that people find alarming. They do not feed on blood, and they can cause a skin reaction in some people that gets attributed to bites — which is exactly how a carpet beetle problem becomes a bed bug scare.

Spider beetles. Rounded, shiny, with long legs and antennae, giving a spider-like impression. They turn up in stored food, in old birds’ nests, in cellars and in accumulated debris. They are roughly bed bug sized, which is the whole source of the confusion.

Cockroach nymphs, particularly the small dark early stages of the German cockroach. Wrong shape once you look — cockroach nymphs are longer and more streamlined, with long antennae and a quicker gait — but at a glance in poor light, a small dark insect near a bed is a small dark insect.

Bat bugs. These are the difficult ones, because they are close relatives and look genuinely similar. They are associated with bats roosting in a structure and they move into occupied space when the roost is disturbed or abandoned. Separating them from bed bugs reliably requires magnification and a look at the length of the fringe hairs on the pronotum. It matters because the correct response involves the bat roost and its exclusion, which is wildlife management work with a seasonal legal framework around it, not a bedroom treatment.

The lesson from all four is the same: a specimen settles it and a description does not. Tape an insect to a card or drop it into a sealed bag rather than photographing it at the limit of a phone camera’s focus, and keep it even if you kill it.

How does the insect actually live?

Hidden, close to the host, and in contact with surfaces on more than one side.

Bed bugs are strongly thigmotactic. Given the choice between an open void and a tight crack, they choose the crack every time, and this single preference explains where they are found. A mattress seam, the piping around a mattress edge, the stapled underside of a box spring, a bolt hole in a bed frame, the joint at the back of a headboard, the gap behind a loose baseboard, the space inside an outlet box — all of these are enclosures with contact on multiple sides.

They are also gregarious. Populations aggregate rather than distributing themselves evenly, which is why one seam can hold a cluster of insects, eggs, skins and spotting while an apparently identical seam a foot away is clean.

Feeding happens when a host is still and asleep. The insect locates a person by cues rather than by sight: exhaled carbon dioxide at distance, then the thermal gradient of a warm body, then chemical signals from skin. It walks to the host, feeds for a period measured in minutes rather than seconds, injects saliva containing anticoagulant and anaesthetic compounds while it does so, and then leaves. It does not stay on the person. That is a meaningful difference from lice or fleas, and it has a direct consequence: bed bugs are moved around in objects — bags, cases, clothing that has been set down, furniture — far more often than on the body.

Timing is behavioral rather than a strict response to darkness. Activity concentrates in the hours before dawn in a normal household, but insects feeding on a night-shift worker who sleeps by day adjust accordingly. Leaving a lamp on is not a strategy.

Between meals they digest, defecate around the harborage, and wait. Adults can persist for months without feeding, and survival extends further in cool conditions because metabolism slows. That is the fact that defeats most amateur attempts at starving them out, and it is why a vacant apartment is not a clear apartment.

Development requires blood at every nymphal stage, so a population’s growth rate is tied to how regularly a host is available. A room slept in every night supports faster growth than a spare room used twice a month — which is why a guest room infestation can smoulder at a very low level for a long time and then accelerate when someone moves in.

Is there a season?

Not biologically, but there is a calendar, and it is a human one.

The insect lives indoors at room temperature and breeds year-round. What varies is the rate at which populations are introduced and moved, and in New York that follows a fairly predictable annual rhythm.

Late spring through summer is the heaviest travel period, and travel is the most common introduction route into a home. Hotel exposure, holiday accommodation, and cases set down on luggage racks all feed residential caseloads from June onward.

Summer into early autumn is the moving season in New York City, and it is the biggest single driver of building-to-building spread we see. Furniture in a van that has carried an infested load, boxes stored in an affected apartment, mattresses left on a sidewalk and taken by someone else, and belongings moved in a hurry all distribute the problem across the city in a matter of weeks. September and October reporting reflects what happened in July and August.

Autumn and the start of the academic year move student belongings back into shared and multi-unit housing.

Winter produces its own pattern. Heating raises indoor temperatures, which speeds development, and people spend more continuous time in their homes, which increases feeding opportunity. A population that was tolerable in October becomes obvious in January without anything having been introduced.

There is one weather-related effect worth naming for landlords and managing agents. Cold outdoor temperatures do not clear an infestation, and there is a persistent folk belief that putting furniture out on a fire escape or a terrace in January will kill them. Sustained cold well below freezing, held for long enough throughout the item, does have an effect, but the conditions that actually achieve it are more demanding than a cold night, and in the meantime the item is being carried through the building’s common areas.

What is genuinely at risk?

Health at the margins, sleep centrally, and — in rented and shared housing — money and legal exposure.

Physically, the reaction to a bite is an immune response to proteins in the saliva, and it varies enormously. Some people develop itchy welts within hours; some take days, which destroys the intuitive link between a mark appearing on Tuesday and an exposure on Monday night; and a significant proportion show no visible response at all while being fed on regularly. Sensitivity also changes with repeated exposure, so a resident who reacted mildly at first may begin reacting strongly weeks later — often misread as a sudden worsening when it is a change in the person rather than in the population. Secondary infection from scratching is the most common actual medical consequence. There is no established role for this insect in transmitting disease to people.

Psychologically, the toll is real and it is regularly underestimated by everyone except the person living with it. Disrupted sleep, anxiety about carrying them to work or to a relative’s home, reluctance to have visitors, and the stigma of being blamed for something that has nothing to do with cleanliness. That stigma has an operational cost as well as a human one: residents who expect to be blamed delay reporting, treat privately with retail products, and sometimes move belongings into other rooms and other apartments — every one of which makes the eventual job larger.

Financially and legally, in a multi-unit New York building the exposure sits mostly in the response. Owners of multiple dwellings carry obligations relating to bed bugs, including disclosure requirements to prospective tenants about a building’s recent history, and any board or managing agent will eventually need to demonstrate what was inspected, what was found and what was done. In hospitality, the gap between a guest’s report and the operator’s action is where liability accumulates. The program structures for those settings are covered under co-op and condo pest control and hotel and hospitality pest control.

What is not at risk: the building itself. This insect damages nothing structurally and has no relationship to housekeeping standards. Clutter makes an infestation harder to inspect and harder to treat because it multiplies the harborage, but it does not cause one.

Where do you look, and how do you actually inspect a bed?

Outward from the sleeping surface, slowly, taking things apart.

Start with the mattress. Run a flashlight beam along every seam at a low angle, so that spotting and skins stand out from the fabric rather than being flattened by direct light. Check the piping, the tags, the handles and the quilting stitch lines.

Then the box spring. This is the highest-yield surface in most bedrooms and the one most often skipped, because the evidence is underneath. The stapled dust cover on the underside has to be lifted or removed. The internal frame, the corner blocks and the staple lines are classic harborage.

Then the bed frame. Joints, bolt holes, the inside of hollow metal tubing, the recesses in a slatted base, and the underside of every horizontal member. Turn the frame over if you can.

Then the headboard, particularly the back face and the wall-mounting hardware. In hotel rooms this is consistently one of the most productive points in the entire room.

Then the immediate surroundings. Nightstands, including drawer runners and the underside of the carcass. The carpet edge along the wall, and the tack strip concealed beneath it. Baseboard joints. Outlet and switch plates. Curtain hems and rod ends. Pictures and anything hanging near the bed.

Then seating. Sofa and armchair seams, under and between cushions, the recesses of the frame, and the mechanism of a recliner. Where a resident has moved to the sofa because the bedroom is uncomfortable, they have usually moved part of the population with them, and the sofa is now the primary site.

Then, in established infestations, the wider room. Behind loose wallpaper, in built-in cabinetry joints, in books, in stored clutter, in curtain folds, inside small appliances and electronics near the bed.

Interceptors under the legs of beds and seating are the most useful low-cost tool available. They catch insects moving to and from the host, they cost very little, and unlike a single inspection they gather evidence over weeks. In a building with a history, standing interceptors in the units adjacent to a confirmed case is a rational monitoring measure rather than an expense.

How does a building move them between units?

Through the same voids that carry everything else, and slowly but reliably.

Apartments are separated by assemblies that are continuous in more places than they appear. Plumbing chases run vertically behind stacked kitchens and bathrooms. Electrical conduit penetrates walls, and back-to-back outlet boxes in a shared wall are effectively a short tunnel between two rooms. Radiator and riser penetrations through floors are frequently open annuli, especially in pre-war buildings where a steam riser passes through a hole nobody ever closed. Party walls in brownstones and attached houses have joist pockets. Dropped ceilings create horizontal voids running past unit boundaries. And the perimeter gap where finish flooring stops short of the framing provides a continuous edge route around a room.

An insect whose whole preference is for tight, contact-rich spaces finds this congenial rather than difficult.

Movement through the structure is slow relative to how fast people move them, but over weeks it is enough to establish a population next door. Two things speed it up considerably. One is displacement: a badly executed or aggressively repellent treatment in one apartment pushes survivors along exactly those routes, which is a common mechanism by which a building’s problem worsens immediately after a resident treats their own unit. The other is human traffic — shared laundry rooms, refuse rooms, elevators, hallway carpet and communal seating all handle infested items, and a resident carrying bedding down to the basement seeds a route everybody uses.

The structural response is sealing: pipe penetrations at every floor, gaps at outlet and switch boxes, the perimeter gap at flooring in affected units, and chase openings. It does not eliminate a population and it is not a substitute for treatment. What it does is stop the building redistributing the problem faster than the treatment resolves it. That work is described in general terms under structural exclusion.

How is an infestation treated?

With a combination, chosen for the room, the contents, the occupants and whether the building has activity elsewhere.

Precise application into harborage. Materials placed into the cracks, seams, voids and furniture framework where the insects actually are, in accordance with the product label and applicable regulation. Done well, this leaves residual activity along the routes the insects travel, which matters in a building where reintroduction is likely. Done badly — broadcast across open surfaces instead of placed into harborage — it accomplishes little and can disperse the population. Resistance to certain insecticide classes is documented in bed bug populations, which is why relying on a single mode of action indefinitely is a poor strategy and why results are monitored rather than assumed.

Heat. A room or its contents is brought to a lethal temperature and held there, with equipment circulating air so that voids and the inside of dense contents reach temperature rather than just the thermostat. It kills every stage including eggs and it treats belongings that are otherwise difficult. Its limits are equally real: no residual effect whatsoever, so an insect walking in from next door the following week is unaffected; deep voids, packed belongings and cold exterior walls in winter can shelter insects below the lethal threshold; heat-sensitive items must be removed; and it needs substantial power and equipment access, which older buildings do not always have.

Steam. Kills on contact including eggs, and is well suited to mattress seams, upholstery, carpet edges and furniture joints where a residual application is undesirable. Slow and precise rather than room-scale.

Vacuuming. Immediate mechanical removal of insects, skins and some eggs, with the contents taken out of the building. It reduces the population at once and makes the room more habitable while the rest of the work proceeds.

Encasements. After treatment, sealing the mattress and box spring isolates anything remaining inside and converts a complicated inspection surface into a smooth one. For the life of the encasement, checking the bed becomes a two-minute job.

Laundering and high-heat drying of textiles, followed by isolating the clean items until the work is finished.

Verification runs on the biology, not on the complaint log. Eggs present at treatment may hatch afterwards and the emerging nymphs need time to encounter whatever has been left for them, so follow-up inspection, interceptors left in place, and monitors in harborage over several weeks are what establish a result. A single visit and a same-day clean bill of health is not something the insect’s life cycle supports.

What actually prevents reintroduction?

Habits, encasements and a building that responds quickly. Sealing helps; nothing seals a person’s luggage.

When traveling, keep luggage off the bed and off upholstered furniture, use the rack away from the wall or the hard surface of a bathroom, and check the mattress seams and the back of the headboard before unpacking. On returning, deal with the contents rather than the case: textiles straight into a hot dryer cycle, and the case itself stored away from the bedroom.

Second-hand furniture deserves real caution, particularly upholstered items and anything with a frame full of joints. Discarded mattresses on a New York sidewalk are frequently there precisely because they were infested.

Keep the encasements on. They are cheap, they last for years, and they turn the most complicated surface in the room into the simplest one to check.

Keep interceptors under the legs. Ongoing, passive evidence costs almost nothing and it turns “I think it might be back” into a fact one way or the other.

Reduce clutter around the bed, not because it causes infestations but because it is the difference between an inspection that means something and one that does not.

In a building, report early and respond without blame. This is the single highest-leverage measure available to a board or an agent. A building where residents report a suspicion the same week, and where the response is prompt and unaccusing, has a materially smaller problem than one where people conceal it for three months. The insects are the same; the delay is what costs the money.

Do not spray anything yourself. Retail aerosols for crawling insects are frequently repellent, and applying them to harborage scatters the population into voids and adjoining rooms. There is also a real fire risk in the use of flammable materials against bed bugs, and it has caused serious harm. If you suspect them, the correct first action is to stop and get the identification confirmed.

Related work

Treatment methods, preparation requirements, building-wide programs and verification are covered in full under bed bug treatment, the parent service for this profile.

Two other library entries share the pathways rather than the biology. The German cockroach travels the same chases, conduit and outlet boxes between apartments, and a building that surveys one usually answers questions about the other. The house mouse uses the same joist pockets and riser penetrations at a larger scale, and the sealing work that addresses one addresses both.

If you have found spotting on a seam, a cast skin, or an insect you cannot identify, get in touch and keep the specimen. Tell us the building type and how many units are involved if you know. The buildings we work in across the city and Long Island are listed under locations.

Treatment for this pest is covered under Bed Bug Treatment.