How Big Are Bed Bugs? (Size Guide)

  • Written By Dan Edwards on January 8, 2018
    Last Updated: December 29, 2020

Bed bugs are tiny little pests that are difficult to see at first glance.

In fact, their size is what makes them so hard to get rid of. You may not even notice them until there’s a full-blown infestation.

They may be tiny, but bed bugs are still problematic. Their bites are irritating, and if you’re not careful, you’ll spread them throughout your home without meaning to.

The bed bugs you find in your home will be in one of three stages of life: adult, nymph or eggs.

How Big Are Adult Bed Bugs?

An adult bed bug is the final part of the life cycle. It will grow to reach the length of an apple seed or around 3/16 to ¼ of an inch long, making it visible to the naked eye.

Bed Bug Size
CC Image courtesy of British Pest Control Association

Their bodies may even look like seeds with legs. Bed bugs are brown with a flat, long oval-shaped body.

When Do Bed Bugs Come Out

However, their bodies change if they have recently fed. Bugs who have been out on the prowl are bloated ovals, almost like little balloons. Their color also changes from a brown to a reddish-brown color.

CC Image courtesy of AFPMB

Why do their shape and color change if they feed regularly?

Bed bugs live on an exclusively blood diet. As they haven’t evolved to eat anything else, they can also go a long time without feeding. If the conditions are right, a bed bug can live on one feed for a few months to up to a year.

Their reddish color comes from the blood they’ve ingested after biting a human, or pet. The bloat also comes from this; they metabolize their food slowly just in case you take a vacation and they can’t eat for a while.

How Big Are Bed Bug Nymphs?

Nymphs are baby bed bugs that have recently hatched but haven’t fed enough to grow into a full-size adult yet.

It’s incredibly hard to see a nymph with the naked eye. They’re even smaller than adult bed bugs and their bodies aren’t brown yet. Instead, they appear almost translucent, which means they blend into their surroundings very well.

Recently-Hatched Bed Bug Nymph – CC Image courtesy of AFPMB

Nymphs only begin to grow into adults when they’ve had their first feed. Yet a nymph doesn’t need to bite right after it hatches. A nymph can wait weeks or even months before it eats for the first time.

CC Image courtesy of louento.pix

Once it eats, it starts to get a bit of color in its body. It will also be slightly rounder.

CC Image courtesy of AFPMB

Nevertheless, they are still hard to see for quite some time.

A nymph needs to feed three to five times before it can become an adult. They could be wandering around your house for up to a year before you even notice them.

Here’s how large nymphs grow with each feed:

  • 1st stage – 1.5 mm
  • 2nd stage – 2 mm
  • 3ʳᵈ stage -2.5 mm
  • 4th stage – 3 mm
  • 5th stage – 4.5 mm

Pictures of a 1st stage nymph having their initial blood meal: 

CC Image courtesy of louento.pix
CC Image courtesy of louento.pix

How Big Are Bed Bug Eggs?

Bed bugs are hatched from eggs laid by adult females. These eggs are almost impossible to see unless they’re right in front of your nose because they only reach the size of a pinhead and females only lay one to five eggs per day.

Bed Bug Eggs
CC Image courtesy of AFPMB

However, one female can lay a total of 500 eggs across her lifespan.

Eggs are only about 1 mm in length and they are white in color. After five days, the eggs will be marked with a small eyespot.

Bed bug eggs – CC Image courtesy of British Pest Control Association

How To Tell a Bed Bug from Other Insects

Understanding how small bed bugs are will help distinguish the difference between bed bugs and other pests found in urban areas.

Knowing the difference is important if you want to get rid of them in a timely manner because different pests require different approaches to extermination.

Here are some other pests commonly mistaken for bed bugs:

Bat Bugs

Bat bugs were the most common insect found in homes prior to the re-emergence of bed bugs in the late 1990s and early 2000s.

Bat Bug

As a member of the same family as bed bugs, these bugs are also brown and oval-shaped. Like bed bugs, they also reach the size of a small apple seed and bloat after they eat.

Bat bugs typically live in a colony of bats – hence the name. If you have bats in your attic or wall, there’s a good chance these insects live among them.

Sometimes, bat bugs decide to break free of the dark confines of a crawl space and enter the home. In most cases, these migrations occur when the bat colonies they live with are exterminated from your home or when the bats choose to leave temporarily.

Without bats, there are not bat bugs. A lack of bats hanging around means these insects won’t be able to reproduce.

Swallow Bug

Swallow bugs are a parasite that lives primarily among cliff swallows. They are also less commonly found among barn swallows.

Like bat bugs and bed bugs, they’re small (like a seed), round, flat, and brown.

Swallow Bug

You’ll find swallow bugs in your home if swallows have built their nests on your home and enjoy your hospitality for a summer. When the swallows migrate, the bugs remain.

By the time March and April arrive, swallow bugs have been in hibernation all winter. Despite this, the swallows themselves aren’t yet back from their warm winter in southern climates. In these cases, the swallow bugs may enter your home and bite.

Carpet Beetles

Carpet beetles aren’t in the same family as bed bugs, but they’re often mistaken for each other.

Carpet beetle larvae have a segmented body, somewhat like bed bugs. However, unlike bed bugs, they don’t have a discernible head. They do, however, have wings, which is an easy way to tell the difference between the two bugs.

Carpet Beetle
Carpet Beetle


Fleas are small, flat insects with easily distinguishable flat hind legs used to jump great distances. They’re smaller than bed bugs, but they better resemble segmented insects than oval-bodied beetles.

Adult Flea
Adult Flea

Many people confuse flea bites and bed bug bites. This confusion is important because bites are often the first sign that you’re facing an infestation.

Bed bug bites look more like mosquito bites than anything else. They may even be confused with an allergic reaction.

People often find they are more sensitive to flea bites than bed bug bites. Children, in particular, are more likely to suffer a reaction from flea bites.

It’s often difficult to see the difference between the two bites, particularly since you likely won’t have seen the perpetrator yet.

The primary difference is in appearance. Flea bites often occur in clusters of small dots on your arms or legs. Fleas have special jaws used to bite you and it looks less like an inflamed bump and more like you’ve been pricked.

These small clusters might appear in random places. In other words, you might have a small patch on your calf and a small patch on your arm.

Bed bugs swell up and are more likely to turn bright red. Bed bugs also tend to bite in rows on your legs because these are easier to access.


Lice and bed bugs are also often confused with each other. Part of this confusion stems from myths suggesting bed bugs live on your body or in your hair.

The truth is your body is inhospitable to bed bugs. Your temperature is too warm for them. Additionally, they like feeding on areas that are easier for them to access, like your legs, rather than trying to navigate through your hair.

Still, when your scalp itches and you aren’t sure what you’re dealing with, it’s easy to confuse the two.

However, bed bugs are significantly larger than lice. Where bed bugs reach the size of an apple seed, lice won’t grow to more than 3mm in length.


Additionally, you’ll find signs of bed bugs in your home. Exoskeletons, eggs, and even the bugs themselves can be seen with the naked eye. Lice tend to live on your body, so you won’t see much evidence of them elsewhere.


You might think that bugs are bugs – all of them are gross. Yet being able to tell the difference between bed bugs and similar insects is important.

Bed bugs don’t spread diseases and in most cases, their bites are relatively harmless. They also aren’t often associated with other infestations, like bats or birds. In other words, bed bugs are a part of living in a crowded area and there’s not much one can do about them.

Meanwhile, flea bites can get infected and cause allergic reactions in some people. Lice can also be harmful; body lice can lead to fever, shivering and aches and pains if left untreated.

As a result, simply letting it go isn’t enough. You’ll need to treat whatever infestation you find appropriately.