Written by: A O’Neill, Licenced Pest Professional

When some people discover they have bed bugs in their home they worry about how quickly they will grow, breed, and spread. As an infestation can quickly get out of hand, having an understanding of what bed bugs look like during different stages of their life cycle can help in identifying and searching for them if you think you have them.


A bed bug’s cycle of life consists of 7 stages starting with the egg. Once the nymph has hatched from the egg it grows through 5 molting periods, taking a blood meal between each molt before finally maturing to the last stage which is adulthood, when they can mate and reproduce their own offspring.

Bed bug life cycle
Bed bug cycle of life


Male bed bugs become particularly interested in mating after a blood meal and will seek out other female bed bugs to mate with.

As bed bugs are not asexual both a male and female are needed to reproduce, and this mating process is called traumatic insemination.

It’s considered traumatic because the male uses his needle-like reproductive organ, called a paramere, to pierce the spermalege, which is a specialized organ on the right side of the female’s abdominal cavity.

When the male has pierced the abdominal area, he then releases his sperm, and over the course of a few hours, it travels to her ovaries for fertilization.

Unfortunately for other recently fed males and nymphs, they are often mistaken for a female and the male bed bugs try to mate with them. The males and nymphs can be severely wounded when their abdominal area is pierced because they don’t have the specialized spermalege organ that protects the females.

However, the males and nymphs are able to excrete an alarm pheromone sending out an alert signal to prevent a mating attack from the unwanted male.

Once fertilization has taken place, the female will now begin laying her eggs, and she can lay around 200 eggs during her lifetime, as long as she has regular access to a blood meal and when temperatures are between 70-80°F (21° – 26°C).


  • A single female bed bug lays approximately 5 eggs a day for 10 days after a single blood meal and could lay between 200-250 during her life cycle.
  • The female will mate again once she has run out of sperm and has fed.
  • 97% of eggs laid will be viable and hatch successfully with an equal ratio of 1:1 of male and female bed bugs produced.
  • Under ideal temperature conditions of 70-80°F, on day six 60% of the eggs will hatch, and around 90% by day nine.
  • Under these ideal conditions and with regular access to a blood meal, the bed bug population size will double in only 16 days.


The bed bug life cycle starts the same as many other insects, and that’s with the egg.


Photo of a cluster of bed bug eggs laid on  cardboard
Cluster of hidden bed bug eggs

Bed bugs don’t have nests, so after mating, the female will move and hide somewhere secluded where she can lay her eggs undisturbed, but she makes sure she’s still close enough to a host so she can feed.

The eggs can be laid in clusters or individually and are laid mainly around the bed frame, mattress, and box spring areas where the host sleeps.

The eggs are laid close to a host because newly emerged nymphs cannot travel far, so if the eggs were laid too far away the nymphs would die of dehydration before they could get anywhere near a blood meal.

The eggs are sticky so they can adhere to cracks and crevices and surfaces such as wood, fabrics, baseboards, and under floorboards. They will also be hard to dislodge so a stiff brush is recommended to remove them.

Read our comprehensive step-by-step guide on how to get rid of bed bugs.

  • Bed bug eggs are oblong and tiny at around 1/16″ (1-1.5 mm) in length, about the size of two grains of sand. They are translucent-white without any indentations making them very difficult to see, especially on light-colored surfaces.
  • Bed bug eggs hatch within 7-10 days (7 days under ideal conditions).
  • Eggs have a red spot after 5 days which is a developing eye.
Close up picture of a cluster of hatched bed bug eggs.
Close up picture of hatched bed bug eggs and nymphs. Image credit: Mohammed El Damir,

When the immature bed bug or nymph has hatched it leaves behind its eggshell which is almost see-through with a round opening at one end (and sometimes a small flap is attached), as can be seen in the picture above and also here for more bed bug images.


Once the nymphs have hatched they will go through 5 molting stages called instars, where they get progressively bigger until they become adults.

Nymphs are almost identical to the adults except they are smaller and have a thinner cuticle (outer skeleton). They are pale when born but develop their brownish coloring as they develop through the molting stages.

A newly emerged nymph (baby bed bug) will seek out a blood meal and feed. These immature nymphs must molt (shed their exoskeleton) five times so they can reach adulthood. However, they must have a blood meal before each molt takes place.

When the nymphs have access to a blood meal they will stay in that molting stage for about the next 5 days before they molt to the next stage.

If a blood meal is not available they will remain in that molting stage and eventually die. However, research suggests that nymphs that haven’t had their first blood meal can live for up to 4 months.

The 5 molting stages are:

1st stage nymph: newly hatched nymphs are 1 mm (1/16″) in size and resemble a sesame seed. They appear almost see-through because they are so pale and are hard to see, but this changes as their bodies become bright red in color once they have a blood meal, which they go looking for as soon as they hatch.

Picture of Bed bug nymph feeding on human and abdomen filling with blood
Close up picture of Bed bug nymph feeding

2nd stage nymph: once the nymph has initially taken a blood meal it is able to molt to this stage and grows to 2 mm.

3rd stage nymph: after feeding again, the nymph molts to the 3rd stage and grows to around 2.5 mm. It is also becoming progressively darker in color at each stage.

4th stage nymph: once again, the nymph molts to this stage after feeding, and grows to 3 mm.

5th stage nymph: this is the final stage before becoming an adult, and they look just like them with a brownish-red color. They will grow to about 4.5 mm.

The nymphs can actually reach adulthood in approximately 21 days in favorable temperature conditions of between 70-80ºF (21-27ºC), but 5 weeks is the average.


  • Adult bed bugs are between 5-7 mm long, about the size of an apple seed, with oval-shaped bodies
  • Bed bugs can take up to 6 times their weight in blood in a single feed
  • Feeding usually takes between 3-10 minutes in which time the body becomes engorged and elongated
  • The male and female can be distinguished by their body shape, the female has a rounded abdomen and is wider than the male, who has a more pointed, V-shaped abdomen
a picture of a bed bug close up in between apple seed and flax seed
Bed bug in between apple seed and flaxseed for size comparison

Once the bed bug nymphs reach adulthood they can now mate and reproduce and can be responsible for 4 successive generations during their lifetime.

Both male and female adults must have regular access to blood meals to keep reproducing and contribute to what will become an ever growing infestation.

The shape of their abdomen changes according to whether they’ve fed or not. If unfed, the abdomen appears flat and their overall body color is brown, but when fed, their color becomes reddish-brown and the abdomen looks swollen and longer.

Did you know that just one fertilized female can cause an infestation of over 5,000 bed bugs within 6 months? This is possible because she will mate with her own male offspring once they have matured and become adults.


It’s difficult to say what the exact life span of an adult bed bug actually is because there are various factors that can affect it.

For instance, laboratory studies have found that the life span of a bed bug, from egg to death, is typically between 6-12 months, under ideal conditions such as ambient temperature and access to blood.

However, the above conditions are not always the same in homes or hotels, as some homes may be colder than others, humidity differs according to location, and homes or cabins may be left for long periods of time – all of these affect how long they live, which is between 2-6 months if they are not entering diapause.

What we do know is that bed bugs develop more rapidly when temperatures are between 70-80°F.

We also know that the adults can generally go without a blood meal for a year or longer by entering into a type of hibernation called diapause when a blood meal isn’t available or when the temperature drops to 55ºF (12.7ºC) or below.

Bed bugs have adapted so well to our environment and have become extremely resilient that over 80% of all nymphs manage to make it to adulthood.

And if that’s not bad enough, bed bugs are able to create their own ideal micro-habitat by squeezing into the smallest cracks and crevices to maintain an ambient temperature and humidity range, which helps them to survive and not dry out when a blood meal is not available.