Does Sunlight Kill Bed Bugs?

Bed bugs hate light exposure and extreme heat. That’s why so many people decide to leave infested items outside during the hottest summer months, aiming to kill bed bugs through sun exposure. It seems like a cost-effective way of getting rid of bed bugs without hiring a pest control company.

Sunlight won’t kill bed bugs on contact. Also, the sun won’t raise temperatures to the 117-120 degrees needed to kill off bed bugs. It’s not possible to consistently achieve this temperature through sun exposure.

Moving things from indoors to the outdoors can spread bed bugs. While sun treatment for bed bugs isn’t an option, you can still kill bed bugs with heat. Read on to find out why bed bugs don’t like sunlight, why sun treatment for bed bugs isn’t a good idea, and much more.

Do Bed Bugs Die in Sunlight?

Everyone knows that bed bugs will do anything to avoid coming out in sunlight. They hide in the darkest cracks they can find to avoid it. You might even think that, like blood-sucking vampires, they would die in the sun. Otherwise, why would they avoid it?

Unfortunately, sunlight doesn’t kill bed bugs. If you go to your room and flip over your mattress, the bed bugs underneath would scurry away, but they won’t die.

All that would happen is that they try and find somewhere else to hide. They’ll look for somewhere dark underneath nearby furniture, or a crack in the floorboards. The idea is to escape from you, not just avoid sunlight. So, if they don’t die in sunlight, why do they hate it so much?

Do Bed Bugs Dislike Sunlight?

According to Clinical Microbiology Reviews, bed bugs are photophobic. This means that they’ll do anything to avoid sunlight. Lots of other bugs are photophobic, too.

This drive is powerful. If you shine a light on a bed bug, even a handheld light, they’ll scurry away quickly. It’s all to do with their basic brain.

All bugs have brains, even if they’re small. And while they aren’t as complex as ours, they’re still good for lots of things. Bed bugs have evolved to process signals and behave accordingly.

do bed bugs die in sunlight?

One of these signals is sunlight. Their eyes don’t pick out details, but they can sense light. Bed bugs can identify whether an area is light, dark, secluded, or open. That’s why bed bugs prefer certain colors over others.

If they sense that an area is bright—especially if it’s very bright—their brains light up. They get an overwhelming urge to get away, and find somewhere safer. Their brains developed to do this over thousands of years of evolution.

Their escape mechanism then kicks in. Their brains are hard-wired to move towards darkness, away from light. In particular, they search out dark red, brown, and black colors. This simple system helps them avoid sunlight and find shelter quickly.

Why Do Bed Bugs Hate Sunlight?

There are two good reasons why bed bugs have been ‘trained’ to avoid sunlight. One is that their evolution dictated they search for dark spaces. Bed bugs are evolved from bat bugs, which live in caves. They like the dark because it’s where their food is.

Bed bugs still have this same reaction. Research shows they will seek out dark places to lay eggs, like bat bugs did, and still do. They know that if they can find somewhere dark, that smells like their favorite food, that they’ll be successful.

Not only that, but dark areas are safer. That’s important because bed bugs can’t defend themselves or their eggs. They don’t have stingers, sharp claws or teeth, or wings to fly away. They’re vulnerable animals, so need to be able to hide.

If they don’t find somewhere secure to hide, they will get squashed or eaten. This applies to their ancestor, bat bugs. Bats eat small insects like bat bugs. So, if the bat bugs don’t hide, they’ll be picked at and eaten. Here’s some information on the different types of bed bugs.

That’s still true of bed bugs too. If you saw one scurrying around, you’d try to squash it. Any bug that does will get killed, and won’t pass on its offspring.

There’s only one circumstance where they will. That’s if they aren’t getting any food at night. If that’s the case, they might try to feed earlier to avoid starvation.

Are Bed Bugs Active in the Daytime?

Because they are photophobic, bed bugs tend not to be active in the daytime. They will stay in their hiding place until it’s night, and it’s safe to come out. But that doesn’t mean they don’t do anything.

The first thing that bed bugs do during the day is to digest their food. When they feed, they fill themselves up completely. Their bodies expand to accommodate all the blood they take in one go. Digestion can, therefore, take a while.

When they aren’t digesting, bed bugs are likely breeding or laying eggs. Bed bugs breed constantly. When they want to lay eggs, the female will head off to find a new harborage. She can do that either in the day, or at night.

Sometimes, they will come out during the day to try and feed. If they are isolated, and don’t have a host at night, they will get desperate. And if the infestation is large, then they will be brazen and come out during the day to feed anyway.

Using Sunlight to Kill Bed Bugs

So, sunlight doesn’t kill bed bugs. But that doesn’t mean there’s no way to harness sunshine to kill them. The heat of the sun can still affect them.

Light doesn’t kill bed bugs, but heat does. How does heat kill bed bugs? It kills all animals in the same way. If the temperature gets high enough, the body’s cells won’t function properly. The animal’s body will quickly stop functioning as it should, and they die soon after.

This is the basis of one of the most common forms of bed bug treatment. Pest controllers use ‘heat treatment,’ where the temperature in a room or house is raised. If it’s upped beyond 117-120 degrees, this can kill bed bugs within minutes.

Temperatures like these aren’t common even in the hottest parts of the world. To be sure of reaching temperatures like these, you would have to take your mattress to Death Valley, which holds the worldwide record.

How to Kill Bed Bugs in Furniture

The simplest method is to take the mattress or piece of furniture, and leave it in the hot sun. Over time, the inside will heat up.

It will help if you seal the bed bugs inside. Let’s say that you want to kill bed bugs inside a mattress. You should apply a mattress encasement before sitting it outside.

The first thing that this will do is protect your mattress from the elements, and other animals. But it will also keep the bed bugs locked inside. Not only that, it will keep the heat inside, too.

If they aren’t stuck inside, they can scuttle out and find somewhere cooler to hide. The first place they’re likely to find in your house. This would, therefore, be a bad idea.

You have to make sure that the bed bugs are killed evenly. This involves turning the furniture upside down, or standing it up, so that all areas heat evenly. This involves a lot of effort, but if you don’t, at least some bed bugs will survive.

How to Kill Bed Bugs in Clothes

You can also kill bed bugs in clothes by bagging them up and leaving them out in sunlight. Garbage bags heat up quickly, especially if they’re black. The clothes inside can be heated more than enough to kill the bed bugs inside.

The same issues apply with this method, however. Only one side will be facing the sun, which means that the other side will be cooler. You, therefore, would have to turn the bags regularly. It’s easier to kill bed bugs in clothes by washing them at a high temperature.

Should You Kill Bed Bugs with Heat and Sunlight?

There are several drawbacks to killing bed bugs by leaving things out in the summer. These drawbacks are important enough that they mean it is never worth trying to do so.

Spreading Bed Bugs

The first is that to put the furniture outside; you’ll need to drag it through your house. Take a mattress, for example. You would have to strip the bed and drag the mattress through the house to leave it outside.

This will spread bed bugs around so that they infest more rooms and hiding places. Bed bugs scatter quickly when disturbed, because of the risks of being squashed or eaten when discovered. They will seek new hiding places.

Far better is to treat the bed bugs where they are without moving their ‘home.’ That way, when you do treat them, they can’t do anything to avoid it.

bed bugs hate sunlight

Uneven Heating

Furniture, mattresses, etc. also take time to heat up. There are lots of hiding places inside and underneath where bugs can escape the sunlight. These areas may never reach the temperature required to kill bed bugs.

Even when the furniture does heat up sufficiently, it won’t all heat up. The underside of the mattress/furniture will be cooler than the side facing the sun. And any drawers in furniture won’t heat up as much either.

You could consistently flip and turn the furniture. However, this will disturb the bed bugs further and encourage them to scatter. It will also still be inconsistent unless you flip the furniture every five minutes.

Inconsistent Heating

The temperature also has to be consistently high. If it doesn’t stay high, only some of the bed bugs will die. Their lifespan will still be reduced, but they can still breed and lay eggs.

This is difficult to achieve when leaving things outside during the summer. The wind or overhead clouds can cool things down quite a lot, even on a sunny day.

And depending on where you put the bags/furniture, the sun might only shine on them for a few hours a day. That’s not to mention the cooler temperatures/less sunshine in the morning, evening, and at night.

That’s why using sunlight to kill bed bugs isn’t a good idea. But that doesn’t mean that there isn’t a way to use heat that works.


How to Kill Bed Bugs with Heat

Better than using the heat of sunlight to kill bed bugs, is heat treatment. This is where a pest controller will heat your home, hot enough to kill bed bugs.

It works in the same way as using sunlight. The big difference is that it’s more consistent. Here’s how a pest controller performs heat treatment:

  1. Before beginning, they will seal up your home. The idea is to stop any bed bugs from moving from room to room, or getting outside.
  2. They will then move your furniture away from the wall, and flip some furniture upside down. The idea is to prevent cold spots from forming, where the heat won’t reach.
  3. They will bring in a large fan heater and leave it plugged in for several hours.
  4. The temperature should reach at least 120 degrees. A good exterminator will know that they have to take it higher, to 140, for example. That’s because furniture heats slowly.

Temperatures of 120 will kill bed bugs within minutes. But because bed bugs live in hiding places, the heat often can’t reach them. Heat treatment aims for much higher temperatures, and works over hours, not minutes.

From looking at how heat treatment works, it becomes clear why just leaving things out in the sun doesn’t work. Treatment needs to be more accurate, consistent, and deadly than that.

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Lou Carter

Hi, I'm Lou. I’ve long been fascinated by bed bugs, ever since a friend’s life was turned upside down. That’s why I’ve put together this specialist site. You’ll find detailed answers to all of your questions on how to get rid of a bed bug infestation. I hope you find it useful!

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