Artificial light can influence the presence and behavior of spiders around human habitats. This interaction is complex, involving both the spiders’ direct perception of light and, more commonly, their indirect attraction through the insects they prey upon.
How Spiders Perceive Light
Spiders possess multiple simple eyes, known as ocelli, which differ significantly from the complex compound eyes of insects or the detailed vision of humans. While many spiders primarily detect changes in light-dark intensity and movement, relying on touch and vibrations for navigation, some hunting spiders, such as jumping spiders and wolf spiders, have more developed vision, often seeing in color and detecting polarized light.
Spider vision often extends into the ultraviolet (UV) spectrum, a range invisible to human eyes. Many spiders have photoreceptors sensitive to UV and blue light, which are shorter wavelengths. Jumping spiders, for instance, can see UV and green light, and some species also perceive red, orange, and yellow hues due to specialized filters in their eyes. This sensitivity to different wavelengths influences their responses to various light sources.
Direct Attraction of Spiders to Light
While less common than indirect attraction, some spider species exhibit direct responses to specific light wavelengths. This direct attraction, known as phototaxis, can play a role in their navigation or even in locating potential mates in species where visual signals are important. For instance, some jumping spiders use UV-reflective patterns for courtship and mate recognition.
However, the direct attraction of spiders to artificial light is often less pronounced than the indirect attraction caused by the presence of their prey. Many spiders do not rely heavily on vision for hunting, instead using vibrations in their webs or on surfaces to detect prey. Therefore, while a spider might perceive certain light wavelengths, it does not necessarily mean they are drawn to the light source itself in the same way nocturnal insects are.
Indirect Attraction Through Insect Prey
The most significant factor in spider accumulation around artificial lights is the indirect attraction facilitated by their insect prey. Many nocturnal insects, including moths, beetles, and mosquitoes, are strongly drawn to certain light wavelengths, particularly ultraviolet (UV) and blue light. These shorter wavelengths are abundant in traditional incandescent, fluorescent, and some “cooler” white LED lights. Insects often navigate using natural light sources like the moon, and artificial lights can disorient them, causing them to aggregate around the light source.
This congregation of insects around lights creates a concentrated food source for spiders. Spiders, being predators, will naturally establish webs or hunt in areas with an abundant supply of food. Consequently, lights that attract a high volume of insects will also indirectly attract spiders seeking to capitalize on this readily available prey. For example, lights emitting wavelengths between 300 and 650 nanometers are particularly alluring to many insects, leading to an increased presence of spiders.
Selecting Lights to Minimize Spiders
To minimize the presence of spiders around outdoor lighting, the most effective strategy involves choosing light colors that are less attractive to insects. Warmer color temperatures, such as yellow, amber, or red LEDs, emit longer wavelengths of light and contain significantly less UV and blue light. Insects are generally less sensitive to these longer wavelengths, making them less appealing.
Amber or “bug lights” are specifically designed to emit light in a spectrum that is less visible to many insects. These bulbs typically have a color temperature around 2000K to 3000K. By reducing the insect population around your lights, you effectively remove the primary reason for spiders to gather in those areas. Switching to warm-colored LED bulbs for outdoor lighting can significantly reduce both insect and subsequent spider activity.