Bed bugs are pretty uniform in size, though that size changes dramatically throughout their six- to 12-month lifespan. A baby bed bug, known as a nymph or instar, goes through five growth stages before reaching bed bug adulthood. Bed bugs also expand and change color after they gorge on you—see for yourself with our full guide to what bed bugs look like.
How big are bed bugs when they hatch?
Nymphs (baby bed bugs) are almost transparent when they hatch, so they’re pretty hard to see with the naked eye. According to the Environmental Protection Agency (EPA)’s clearinghouse on bed bugs, a nymph is about 1.5 millimeters—about the size of a pinhead. The nymph will continue to grow but only if it takes a blood meal. After feeding, it will shed its skin (molt) and advance to the next stage. Nymphs grow about a half-millimeter during each stage. If a nymph doesn’t find a host for a blood meal, it will die before advancing to the next stage.
How big are bed bugs?
Adult bugs average around five millimeters (picture an apple seed) long and have a broad-shaped oval body that is flat and brownish to reddish brown. Bed bugs have two antennae, six legs, and an abdomen with 11 sections that expand when they take a blood meal. The tips of the abdomen are usually pointed in males and more rounded in females. Don’t fall for the myth that the bugs are microscopic—or any of these other common bed bug myths.
How big are bed bugs after they bite us?
A bed bug will probe your skin a few times before it finds a good spot to latch on. They’ll feed for about five to ten minutes before releasing. “The bugs change color to a deep, dark red and they will become elongated and change from a flattened bug to quite a large, slow-moving, full, fat bug,” says Jody Green, PhD, an urban entomologist at the University of Nebraska–Lincoln. “They can consume up to three times their body weight in a single feeding, and then they will waddle away to hide, rest, and digest.” Once full, they’ve reached their largest size—up to six millimeters in length, and cylindrical in shape. After a bed bug begins the digestion process back at their harborage (the name for their hiding spot), the bug will start to return to normal and become flat and oval again. Now that you know what bed bugs look like, find out the warning signs you’re about to have a bed bug problem.