What size are bed bugs and what do they look like? - briefly
Adult bed bugs measure about 4–5 mm in length (roughly the size of an apple seed) and are flat, oval, and reddish‑brown when unfed, turning darker after feeding. Nymphs are smaller, translucent to light brown, and become progressively darker with each blood meal.
What size are bed bugs and what do they look like? - in detail
Bed bugs (Cimex lectularius) are small, oval‑shaped insects. Adult individuals measure approximately 4.5–5.5 mm in length and 2–3 mm in width, comparable to the size of an apple seed. Their bodies are flat when unfed, allowing them to slip between fabric fibers and mattress seams. After a blood meal, they expand to about 6–7 mm long, becoming noticeably more rounded and darker in color.
Key visual traits include:
- Color: Light brown to reddish‑brown when unfed; deep burgundy or almost black after feeding.
- Shape: Broad, dorsoventrally flattened, with a tapered abdomen ending in a pointed tip.
- Surface: Smooth, non‑shiny cuticle lacking wings or noticeable hairs.
- Eyes: Small, bean‑shaped ocelli positioned near the front of the head.
- Antennae: Four segmented, slender, and hidden beneath the head when at rest.
- Mouthparts: Piercing‑sucking proboscis concealed within a groove on the ventral side, adapted for drawing blood.
Nymphs resemble adults but are smaller, ranging from 1.5 mm (first instar) to 4 mm (fifth instar). Their coloration remains lighter throughout development, becoming progressively darker after each blood meal. All stages exhibit the characteristic “shield‑shaped” dorsal plate, which can be observed when the insect is viewed from above.
When examined under magnification, the exoskeleton displays fine punctate markings and a series of tiny bristles (setae) along the legs. The legs consist of five segments, each ending in a claw that aids in climbing smooth surfaces. The dorsal abdomen bears a faint, pale line that runs longitudinally, useful for distinguishing bed bugs from similar insects such as carpet beetles or bat bugs.