Are Spiders Attracted to Light? What The Scientists Discovered

Are spiders attracted to light? There’s no denying that spiders are fascinating creatures, but many of us would rather not have them on our deck. Will turning off the deck lights help deter them? Scientists have been studying this phenomenon for years and have come up with some pretty interesting findings. We’ve got the scoop and it is time to share what we discovered.

Are Spiders Attracted To Light? (Brief Version)

It’s a common belief that spiders are attracted to light, but is there scientific evidence to support this claim? In brief, some spiders are attracted to incandescent artificial lighting at night. This is mainly because this kind of light attracts insects. As you know, spiders are predators, and insects are their primary food source. So it makes sense that spiders would be attracted to this kind of light. The spiders that show this behavior tend to have good eyesight. Interestingly halogen lights were not as attractive to insects and did not seem to attract spiders as readily.

A Quick Introduction to Spiders

Scientists have classified spiders as arachnids. Arachnids are part of the family of arthropods (animals that have jointed legs). Ticks, mites, and scorpions are also part of the arachnid family. There can be found in most habitats around the world. So far, just over 45,000 different spiders have been identified.

They can be easily distinguished from insects by the number of legs. Spiders have eight legs, while most insects have six. Another difference between spiders and insects is that a spider’s body is divided into two parts (the cephalothorax and the abdomen). In contrast, an insect’s body is divided into three parts (the head, thorax, and abdomen. This post delves into the anatomy of spiders.

Spiders are carnivores and feed mainly on insects. They have well-developed poison glands that paralyze their prey. In addition, many spiders can spin silk. The use of silk varies among spiders, but it is generally used for building webs.

For the most part, spiders are harmless to humans, although there are some notable exceptions. You can read about some of those here.

They are usually considered helpful animals as they feed on the harmful insects that plague our lives as gardeners. They also feed many birds, so they play an essential part in the food chain.

Insects transport a variety of fungal and bacterial infections from one plant to the next. The fewer insects in your garden, the less likely diseases will be transferred from plant to plant. Garden spiders might also help prevent plant diseases by stopping the spread of disease.

Weird and wild spiders: Did you know there’s a spider with a butt that looks like Pikachu?

How Do Spider See?

Did you know that spiders can have up to eight eyes? Despite this, however, most spiders have poor vision. Most spiders can only detect light and dark intensity changes. They use other senses such as touch, vibration, and taste to navigate and catch their prey.

Some spiders have eyelike structures, called median eyes, that can help them navigate while hunting. Some spiders have good vision. They use this vision primarily for hunting and capturing prey. It’s also crucial for recognizing mates, rivals, and predators. This group of spiders includes

Jumping spiders (Salticidae)
Flower spiders (Thomisidae)
Wolf spiders (Lycosidae)
Net casting spiders (Deinopidae)

Jumping spiders are particularly fascinating because they have developed eyes that are, in essence, a tube with a lens at either end. They can adjust the angle and shape of these lenses, allowing them to focus and zoom. How cool is that?

Interested to learn more about spiders? Read our post about the kinds of spiders you will find in the grass. It has incredible pictures!

What Types Of Spiders Are Attracted To Light?

Have you ever turned on the light and found that spiders suddenly appear? No, me either! However, I uncovered some fascinating research that indicates that certain species of spiders are attracted to artificial light. Let’s take a quick look at some of the studies.

Spiders Attracted To Green Lights

Scientists have discovered that some spiders, such as the wolf spider, are attracted to green wavelengths. The eyes of Jumping spiders contain two types of light-detecting cells. The first is sensitive to ultraviolet light are the other picks up a green light. Scientists have found that jumping spiders are particularly attracted to green lights. While interesting, this isn’t going to impact homeowners much as most of us do not use green lights outside.

Spiders Attracted to Artificial Incandescent Lights

Orb web spiders

I looked at three papers (sources listed below). The first was conducted in Vienna. where scientists looked at the behavior of the orb-web spider called Larinioides sclopetarius. This spider is active at night and lives near water. Scientists found that these spiders are attracted to artificial light sources, such as the artificially lit handrails on footbridges. They counted the number of spiders and webs on both lit and unlit handrails of bridges in Vienna. The results showed significantly more spiders and webs on the lit handrails.

In a laboratory experiment, female orb-web spiders were given a choice between an artificial light source and a dark area. The results showed that most spiders preferred to build their webs near the light source. This suggests that spiders are attracted to light rather than just being opportunistic web builders.

Even more interesting, they repeated the experiment with spiders born and raised in the laboratory. The results were the same, suggesting that this behavior is genetically determined rather than learned. In other words, Larinioides sclopetarius is wired to be attracted to artificial light.

Web Builders And Their Webs on Historic Buildings

The second study was conducted in Turin, Italy. Over a year, scientists studied the web building habits of a spider called Brigitte Civica in the arcades of historical buildings.

Scientists looked at the density of the webs on selected arcade ceilings. They collected information on what preferences were shown by the spiders. The results showed significantly more webs at sites with higher light intensity. Particularly those lit by incandescent lamps as opposed to Halogen lamps.

They could support larger colonies of spiders because of the favorable condition (abundance of insects). So, it would seem that the spiders were attracted to the incandescent lamps. However, the study’s authors cautioned that it is not clear if the lit ceilings were intentionally chosen by the spiders. Further studies would be needed to show that spiders deliberately choose the lit top on their own.

Jumping Spiders Taking Advantage of Artificial Lights

The final study shows an exciting behavior change in a jumping spider known Platycryptus undatus. These spiders typically hunt during the day. However, two scientists noticed that there were a number of these spiders hunting insects at night.

The spiders were observed moving to an outdoor porch light base to hunt just after dark when the lamp was turned on. They would wait for insects to fly within range and then lunge at them or stalk and pounce on insects out of reach.

These spiders have taken advantage of the easy hunting made possible by artificial lights. This change in hunting behavior was obviously in response to artificial light.

Further studies are needed to determine what caused these spiders to hunt at night rather than during the day. It could be that the artificial light sources are attracting spiders and encouraging them to leave their nighttime hiding places. It could be that vibrations from the increased insect activity around the lamp got the spiders to leave their shelters. Whatever the cause, the incandescent light had a definite impact on those spiders.

Why Are Spiders Attracted To Light?

There are some interesting theories. Mostly, it has to do with the easy hunting that light sources make possible. In well-lit areas, there are more insects for spiders to prey on. This is especially true for flying insects that are attracted to light themselves.

Some scientists believe it is an instinctive response that is hard-wired into spiders. The thought is that this behavior evolved because it gave spiders an advantage in terms of foraging success. After all, more food means more spiders.

Insects were more numerous near the lights than in locations without light. This isn’t surprising, as insects are drawn to the lights. Why does that happen? Scientists have several theories.

Artificial Light Disorientates Insects navigation System

The most popular theory is that flying insects approach a light source not because they’re “attracted” to it. What actually happens is that the light confuses them and disorients their natural sense of direction.

Insects rely on the moon and stars to navigate. They use these celestial objects as fixed points to help them find their way. When your outdoor lights turn on, they create a fixed point that’s brighter than the moon and stars. Consequently, the insects start flying towards your light instead of continuing on their original path. When they reach the light source, insects become disoriented due to the light’s unnaturally close proximity. This drives them to circle around or crash into it and attempt to figure out where to go.

The Insects Are Confused By the UV Light

Ultraviolet light is invisible to us, but it’s like a beacon for night-flying insects. Many flowers reflect small amounts of ultraviolet light. The flowers use this ultraviolet light to attract pollinators like moths. Your porch lights also produce ultraviolet light, causing moths to mistake them for flowers.

Insects Are Trying to Escape Predators

It’s conceivable that insects are drawn to the light to flee from possible harm. In essence, the light signals an escape route in dangerous situations. Light indicates that no predators or obstructions are in the way, so it is a clear route to safety. This could explain why insects often crash into light sources, mistaking the light for a clear path to safety.

Whatever the reason, one thing is clear, insects flock to incandescent lights at night, resulting in more food for spiders. And as we’ve seen in the studies above, spiders are definitely taking advantage of this.

Spiders who build webs near artificial lights will have a better chance of catching prey. The number of potential prey is higher near artificial lights, so spiders which take advantage of this increase their chances of survival and reproduction.

How Do Spiders Choose Their Foraging Sites?

The place where a spider builds its web is determined by the species. Spiders from different families have different needs.

It takes 30 minutes to an hour for the average spider to build a web. Spiders must choose a site that will provide enough food to sustain them. Choosing the wrong spot for a web will result in a lower chance of survival.

Spiders will benefit from finding the right site as fast as possible. Having to relocate takes time and energy. If a spider can find an optimal place the first time, it will be more likely to survive and reproduce. It also increases the chance of being caught by a predator.

A spider must also be able to protect itself from predators while it is building its web and catching prey. The site must provide shelter or camouflage so the spider can avoid being eaten.

The availability of food and shelter is the two main factors that spiders consider when choosing a site. Studies show that spiders do not find good quality foraging sites by taking the time to sample possible locations. Instead, the spiders actively choose patches that provide a good food supply and shelter. Spiders are observed to abandon webs when the food supply at a given site is inadequate.

Spiders often favor locations with artificial light because those lamps attract a plentiful supply of prey. It stands to reason that spiders in a prey-rich site will have an advantage over spiders living in places with fewer insects.

Finding this post helpful? See all our wildlife and animal posts.

What Does This All Mean for Homeowners?

Artificial lights on your deck or front porch are going to attract spiders. It could be that spiders are wired to build webs near these lights or follow the food. It doesn’t really matter, does it?

To sum it up, artificial light means increased insect activity, leading to increased numbers of spiders. The why and wherefores are fascinating but don’t change the basic facts.

You have two options if you want to reduce the number of spiders around your house and on your deck

Swap your incandescent bulbs for Halogen or outdoor bug lights.
Turn off porch lights and deck lights at night.

Final Thoughts

Hopefully, this article has helped you understand why spiders are attracted to light. We hope you found this information as fascinating as we did. It’s incredible to think that such tiny creatures can have such a complex and interesting world of their own. Next time you see a spider web on your porch light, you’ll know why it’s there! If you enjoyed this post and found it helpful, please do us a favor and share it with others who may be interested.

How I Researched For This Post

This post about spiders and light results from about 5 hours of research. I work in an academic library, so I have access to many scientific journals and books. When I write a post, I look at the scientific literature and use that information. I used the following resources.

Heiling, A. Why do nocturnal orb-web spiders (Araneidae) search for light?. Behav Ecol Sociobiol 46, 43–49 (1999). https://doi.org/10.1007/s002650050590
Mammola, S., Isaia, M., Demonte, D., Triolo, P., & Nervo, M. (2018). Artificial lighting triggers the presence of urban spiders and their webs on historical buildings. Landscape and Urban Planning, 180, 187-194.
Frank, K. D. (2009). Exploitation of artificial light at night by a diurnal jumping spider. Peckhamia, 78(1), 1-3.
Australian Museum (2022, April 21). How Spiders See The World. https://australian.museum/learn/animals/spiders/how-spiders-see-the-world/
Pearson G (2014, April 23). Spider Vision Made Clear. Wired. https://www.wired.com/2014/04/spider-vision-made-clear/