What do domestic bed bugs look like, and where do they hide?

Understanding Bed Bugs

Visual Identification of Adult Bed Bugs

Size and Shape

Domestic bed bugs are small, wing‑less insects that typically measure between 4 mm and 5 mm in length when unfed, expanding to about 6 mm–7 mm after a blood meal. Their bodies are roughly 2 mm wide, giving a compact, flattened profile that facilitates movement through fabric seams and cracks.

Key characteristics of their shape include:

Oval, elongated form with a rounded anterior and a slightly tapered posterior.
Dorsal surface covered by a hardened exoskeleton (hemelytra) that protects the abdomen.
Six legs positioned midway along the body, each ending in a claw for gripping fibers.
Antennae consisting of five segmented rods, visible from a lateral view.
After feeding, the abdomen becomes markedly distended, giving a more bulbous appearance while retaining the overall flatness.

These dimensions and structural traits enable bed bugs to hide in mattresses, box springs, headboards, and upholstery, where narrow spaces and tight folds provide concealment.

Coloration

Domestic bed bugs (Cimex lectularius) display a distinctive coloration that aids identification. Adults are oval, flat, and range from reddish‑brown to deep mahogany when unfed. After a blood meal, the abdomen expands and the color becomes a brighter, almost brick‑red hue. Nymphs progress through five instars, each retaining a lighter, amber‑tan shade that darkens with successive molts. The head and thorax are consistently darker than the abdomen, creating a two‑tone appearance. Eyes are small, dark lenses, and the antennae and legs are pale, matching the body’s overall brown palette.

The insects’ coloration blends with common hiding sites, making visual detection challenging. Dark, concealed environments such as mattress seams, box‑spring crevices, and upholstered furniture cushions provide backgrounds that mask the reddish‑brown body. Light‑colored bedding or furniture edges can reveal the contrast between the bug’s darker dorsal surface and its surroundings, especially after feeding when the abdomen brightens. Effective inspection relies on recognizing the color shift from dull brown in unfed stages to vivid red in engorged adults, and focusing on typical harborages where this contrast is most apparent.

Unique Features

Domestic bed bugs exhibit a set of morphological traits that enable reliable identification. Adults measure 4–5 mm in length, display a flat, oval body, and possess a reddish‑brown hue that darkens after feeding. Their thorax bears two small, curved wing‑like structures called hemelytra, which are non‑functional for flight. Six antennae segments taper to a point, and each leg ends in a claw that grips fabric fibers. The abdomen features a pronounced “c‑shaped” fold, visible when the insect is viewed from above.

Key physiological characteristics include:

A soft, flexible exoskeleton that allows the bug to flatten under mattresses and into tight crevices.
A pair of scent glands that release a distinct, musty odor when the insect is disturbed.
An ability to survive prolonged periods without a blood meal, remaining viable for months.
Rapid molting cycles; nymphs progress through five instars, each stage retaining the same general shape but increasing in size.

Hiding behavior reflects these features. Bed bugs preferentially select flat, protected surfaces that accommodate their flattened body and enable close contact with hosts. Common concealment sites are:

Mattress seams, tags, and box‑spring voids.
Bed frame joints, headboard cracks, and upholstered furniture cushions.
Wall baseboards, picture frame backs, and electrical outlet covers.
Luggage folds, clothing folds, and suitcase interiors during travel.

These distinctive physical and behavioral attributes simplify detection and inform targeted control measures.

Recognizing Immature Bed Bugs (Nymphs)

Nymphal Stages and Appearance

Domestic bed bugs pass through five nymphal instars before reaching adulthood. Each stage can be distinguished by size, coloration, and the presence of blood meals.

First instar: approximately 1.5 mm long, translucent to pale yellow, no visible eyespots, abdomen flat. Often found near eggs, hidden in seams of mattress covers or behind baseboard molding.
Second instar: 2 mm long, slightly darker yellow, faint red–brown spotting after a blood meal. Frequently located in mattress folds or behind picture frames.
Third instar: 2.5–3 mm, deeper amber hue, distinct reddish‑brown spots if fed. Commonly hides in cracks of headboards, wall voids, or under upholstered furniture.
Fourth instar: 3.5 mm, marked by a more pronounced reddish abdomen and visible eyespots. Typically concealed in box‑spring seams, behind electrical outlets, or within wall cavities.
Fifth instar: 4–5 mm, coloration approaching that of the adult—brown‑red with a lighter abdomen after feeding. Occupies larger refuges such as the underside of bed frames, behind curtains, or inside luggage compartments.

Nymphs retain the same flattened, oval body shape as adults, allowing them to squeeze into narrow crevices. Their exoskeletons are soft until the final molt, after which the cuticle hardens and darkens. Identification relies on measuring length, noting translucency versus pigmentation, and observing the presence of recent blood stains, which turn the abdomen bright red for a short period after feeding. Recognizing these characteristics helps locate the insects in typical hiding places throughout residential environments.

Color Changes During Development

Domestic bed bugs undergo a series of color transformations as they progress from egg to adult, a pattern that directly influences their visual identification and the sites where they are most likely to be found.

Egg: Translucent white, barely visible against fabric or paper.
First‑instar nymph: Light amber, often mistaken for a speck of dust.
Second‑instar nymph: Darker amber, gaining a faint brown hue.
Third‑instar nymph: Medium brown, more conspicuous on light‑colored surfaces.
Fourth‑instar nymph: Dark brown, approaching adult pigmentation.
Adult: Reddish‑brown to mahogany, with a glossy, flattened body.

The progressive darkening coincides with increased blood intake and exoskeleton hardening. Early instars, being paler, blend into white or cream linens, making detection difficult in sheets, pillowcases, and mattress tags. Mid‑stage nymphs, with their medium brown tone, contrast against light fabrics but remain camouflaged on darker upholstery, baseboards, and cracks in wall paint. Fully developed bugs, characterized by a deep mahogany color, are readily visible on light surfaces yet become less noticeable when concealed in crevices, behind wallpaper seams, or within mattress seams where shadows mask their hue.

Understanding these color shifts enables precise inspection: focus on pale, translucent spots for eggs; search for light amber specks in seams and folds; examine darker brown insects in hidden cracks and under furniture. Accurate identification at each developmental stage reduces the risk of overlooking a growing infestation.

Bed Bug Eggs

Description of Eggs

Bed bug females lay tiny, oval eggs that measure approximately 0.5 mm in length and 0.3 mm in width. The shells are smooth, translucent to whitish, and become slightly opaque as the embryo develops. Each egg contains a single embryo and is attached to a substrate by a minute, adhesive stalk.

Eggs are deposited in locations that provide protection from disturbance and temperature fluctuations. Common sites include:

Crevices in mattress seams and box‑spring frames
Edges of headboards and footboards
Behind baseboard molding and wall cracks
Folds of upholstered furniture cushions
Inside luggage compartments and suitcase zippers

These microhabitats keep the eggs concealed and maintain the humidity needed for successful incubation. The placement strategy aligns with the insect’s overall preference for tight, dark spaces near host resting areas.

Common Locations for Eggs

Domestic bed bugs deposit their eggs in locations that provide protection from disturbance and easy access to a blood meal. Female insects lay clusters of 5‑10 eggs, each about 1 mm long, and conceal them where movement is minimal.

Seams and folds of mattresses, especially along the inner edges of the fabric.
Box‑spring interiors and the stitching that joins the fabric to the frame.
Cracks, joints, and hollow spaces in bed frames, headboards, and footboards.
Crevices of upholstered furniture, including sofa cushions, chair backs, and recliner mechanisms.
Baseboard gaps, wall–floor junctions, and behind loose wallpaper or wall hangings.
Behind picture frames, mirrors, and decorative wall art where the backing creates a narrow cavity.
Luggage compartments, suitcase seams, and travel bags that have been stored near infested areas.
Electrical outlet covers, switch plates, and wiring cavities that remain undisturbed.
Underneath floorboards, carpet edges, and in the voids of removable floor tiles.

These sites share the characteristics of limited airflow, darkness, and proximity to human hosts, allowing eggs to develop safely until the nymphs emerge.

Hiding Places of Bed Bugs

Common Infestation Zones

Sleeping Areas

Domestic bed bugs are small, oval insects about 4–5 mm long when unfed and 6–7 mm after a blood meal. Their bodies are flat and wingless, colored reddish‑brown, with a lighter, almost ivory abdomen that becomes more engorged after feeding. Six legs end in tiny claws, and the antennae are short and segmented. This morphology allows the pest to move easily into narrow crevices.

In sleeping environments, bed bugs exploit the numerous micro‑habitats that provide darkness, warmth, and proximity to a host. Typical concealment sites include:

seams, tufts, and tags of mattresses and box springs
folds and joints of headboards, footboards, and bed frames
cracks in wall plaster, baseboards, and behind wall hangings
interior of nightstands, dressers, and other bedroom furniture
under loose floorboards, carpet edges, and area‑rug underlays
behind electrical outlets, light switches, and wiring conduit

These locations remain undisturbed for extended periods, allowing the insects to hide during daylight and emerge at night to feed. Regular inspection of the listed areas, combined with vigilant monitoring of bed bug physical traits, provides the most reliable means of early detection in sleeping quarters.

Seating Areas

Domestic bed bugs are small, oval insects about 4–5 mm long, flat-bodied, and reddish‑brown after feeding. Their bodies become more elongated and lighter in color when unfed. Eyes are absent; they rely on antennae and sensory pits to navigate. These traits enable them to infiltrate tightly woven fabrics and narrow crevices found in residential furniture.

Seating areas provide numerous microhabitats that accommodate the insects’ need for darkness, warmth, and proximity to a blood source. Typical refuges include:

Cushion seams and folds where fabric overlaps
Underneath seat cushions and behind removable covers
Inside sofa or chair frames, especially at joints and screw holes
Recliner mechanisms, gear boxes, and pivot points
Under armrests and along side‑panel stitching
Gaps between legs and floor, particularly when furniture rests on carpet

Inspection should begin with visual examination of these zones, using a bright light and magnification if possible. Detectable signs are live or dead insects, rust‑colored fecal spots, and translucent shed skins. When an infestation is confirmed, isolate the affected seating, launder removable fabrics at ≥ 60 °C, and apply approved residual insecticide to hidden structures. Vacuuming the entire seating set removes eggs and nymphs, reducing population rebound. Regular monitoring of the identified locations prevents reestablishment.

Wall Structures and Furniture

Domestic bed bugs are tiny, flat, oval insects measuring 4–5 mm when unfed and expanding to about 7 mm after a blood meal. Their bodies are reddish‑brown, fading to a lighter hue after feeding. Six legs end in tiny claws, and the abdomen displays faint, pale stripes visible under magnification.

In wall assemblies, bed bugs exploit any narrow opening. Typical concealment points include:

Cracks in plaster or drywall
Gaps behind baseboards and molding
Electrical outlet frames and switch plates
The voids behind wallpaper or wall‑papered panels
Wall cavities accessed through damaged studs or unfinished seams
The backs of picture frames, mirrors, and wall‑mounted shelves

Furniture offers numerous microhabitats. Common locations are:

Mattress seams, especially around the stitching and tags
Box‑spring folds and the underside of the fabric cover
Headboard joints and the space between the headboard and wall
Upholstered chair cushions, particularly where the fabric meets the frame
Wooden bed frames, focusing on drilled holes, dowel joints, and loose slats
Sofa or recliner frames, especially the internal webbing and spring coils

Bed bugs move readily between these sites, using their flattened bodies to infiltrate tight spaces. Regular inspection of wall cracks, outlet covers, and furniture joints is essential for early detection.

Less Obvious Hiding Spots

Electronics and Appliances

Domestic bed bugs are small, oval insects about 4–5 mm long, flat-bodied, and reddish‑brown after feeding. Unfed individuals appear lighter, nearly tan, with a distinct, elongated shape and no wings. Their antennae are short, and each segment bears a pair of tiny, hair‑like bristles.

Electronic devices and household appliances provide warm, protected micro‑environments that mimic the crevices near beds and furniture. Heat generated during operation, combined with limited disturbance, creates ideal conditions for the insects to develop and reproduce.

Common items that harbor infestations include:

Bed‑frame wiring and power strips
Television and computer chassis
Vacuum cleaners and portable fans
Refrigerators and freezers (especially seals and insulation)
Washing machines and dryers (gaskets and drum interiors)

Inspection procedures:

Power off and unplug the equipment before examination.
Use a bright flashlight to view seams, vents, and interior cavities.
Look for live insects, shed skins, or dark fecal spots resembling pepper grains.
Apply a fine‑toothed brush to dislodge hidden specimens for visual confirmation.
If evidence is found, isolate the device, treat it with approved insecticide, and wash removable components at high temperatures.

Personal Belongings

Bed bugs are small, wingless insects about 4–5 mm long when fully engorged. Their bodies are oval, flattened, and reddish‑brown, becoming more swollen and darker after feeding. Nymphs resemble adults but are lighter in color and lack the distinctive orange‑red abdomen. Their heads are hidden beneath the thorax, and they have six legs and two short antennae.

Personal items provide convenient travel and storage sites for these pests. They can be transported in clothing, shoes, backpacks, suitcases, and small fabric accessories. When not feeding, bed bugs seek tight seams, folds, and creases where temperature and humidity remain stable.

Typical hiding spots on personal belongings include:

pockets and interior seams of jackets and pants
linings and zippers of bags and luggage
inside shoe soles and laces
folds of blankets, towels, and scarves
fabric tags and label pockets

Inspecting these areas after travel or storage, and washing or heat‑treating items at 60 °C (140 °F) for at least 30 minutes, reduces the risk of infestation. Regular vacuuming of luggage interiors and using sealed plastic bags for clean clothes further limits the chance of bed bugs establishing a presence on personal possessions.

Cracks and Crevices

Domestic bed bugs are small, oval insects about 4‑5 mm long, flattened dorsally, wingless, and reddish‑brown after feeding. Their bodies expand to a lighter, swollen appearance when engorged, making them visible against light backgrounds.

Cracks and crevices provide the narrow, protected environments bed bugs require. They occupy any gap wider than 1 mm but narrower than 5 mm, allowing the insect to squeeze in while remaining concealed. Common locations include:

seams of mattresses and box springs
joints of headboards and footboards
gaps behind baseboards and crown molding
fissures in wall plaster or drywall
openings around electrical outlets, light switches, and wiring conduits
cracks in furniture frames, especially wooden or upholstered pieces

Inspection should focus on these areas with a bright light and magnification. Look for live insects, translucent exuviae, and dark fecal spots approximately the size of a pinhead. Probing suspicious gaps with a thin instrument can reveal hidden specimens.

Effective control begins with eliminating entry points. Apply silicone or acrylic caulk to seal seams and fissures, replace damaged baseboards, and tighten loose furniture joints. Follow sealing with targeted insecticide treatment or heat exposure to eradicate remaining bugs. Continuous monitoring of cracks and crevices ensures early detection of reinfestation.

Signs of a Bed Bug Infestation

Physical Evidence

Domestic bed bugs are small, oval insects about 4–5 mm long when fully fed, flattening after a blood meal. Their bodies are reddish‑brown, turning paler after digestion, with a distinct “c‑shaped” posture when disturbed. Nymphs resemble adults but are lighter, lack fully developed wings, and increase in size with each molt. Eggs are tiny (≈0.5 mm), white, and adhere to surfaces in clusters.

Physical evidence of an infestation includes:

Live adults or nymphs observed on skin, bedding, or furniture.
Exuviae (shed skins) left after each molt, typically found near hiding sites.
Fecal spots, dark‑brown or black specks resembling pepper, often on mattresses, sheets, or walls.
Small blood stains on linens, pillowcases, or upholstery, usually appearing as faint reddish spots.
Egg clusters, white and difficult to see without magnification, attached to seams or crevices.

Bed bugs select concealed environments that protect them from disturbance and facilitate access to hosts. Common concealment locations are:

Mattress and box‑spring seams, tags, and piping.
Bed frame joints, headboard cracks, and underheadboard panels.
Sofa cushions, especially zippered seams and fabric folds.
Furniture crevices, such as chair legs, drawer slides, and cabinet backs.
Baseboards, wall voids, electrical outlet covers, and behind wallpaper.
Cluttered areas, including piles of clothing, books, or luggage.

Detecting the described physical signs in these specific sites confirms the presence of domestic bed bugs.

Scent Indicators

Domestic bed bugs are small, flat insects, reddish‑brown, approximately 4–5 mm long when unfed. Their bodies become engorged and darker after feeding on human blood. In residential settings, they favor concealed locations close to a host’s sleeping area.

Scent indicators provide a reliable early warning of infestation. Common olfactory clues include:

A sweet, musty odor reminiscent of coriander or ripe strawberries, produced by the bugs’ defensive glands.
A faint, sour, or metallic smell emanating from crushed or dead specimens.
Residual odor from fecal spots, which contain digested blood and emit a characteristic iron‑like scent.

These odors are most detectable near the insects’ refuges. Typical hiding places are:

Mattress seams, box‑spring cavities, and bed frames.
Upholstered furniture, especially cushions and crevices.
Wall voids, baseboard cracks, and behind picture frames.
Luggage racks, closets, and electrical outlet covers.

Professional detection dogs are trained to recognize the specific volatile compounds associated with bed‑bug scent. Their use complements visual inspections, especially in hard‑to‑reach spaces where the insects remain hidden.