Quick Answer
Most spiders have eight eyes, but some have fewer or even no eyes at all. The majority of spiders have six or eight eyes, arranged in patterns that help them sense objects and motion around them. Having multiple eyes gives spiders a wide field of vision to spot prey and avoid predators. However, some spiders like the blind cellar spider and Liphistius trapdoor spider have no eyes or vestigial non-functioning eyes. The number and placement of a spider’s eyes depends on its hunting style and habitat. Web-building spiders often have very acute eyesight to detect prey in their webs, while ground spiders rely more on touch and vibration cues.
How Many Eyes Do Spiders Have?
Most spiders have eight eyes, which is the ancestral state for this ancient group of invertebrates. Having eight eyes arranged in four pairs gives spiders an almost 360-degree field of vision, allowing them to easily spot prey, predators, and mates. Here are some key facts about spider eyes:
| 6 or 8 | The number of eyes most spiders have |
| 4 | The maximum number of eye pairs spiders can have |
| 720° | The potential field of vision for spiders with 8 eyes |
| Main eyes | The largest pair of eyes, facing forward to target prey |
| Secondary eyes | The remaining smaller eye pairs giving peripheral vision |
While most spiders have six or eight eyes, some species are exceptions:
– Jumping spiders have only six eyes, but their main pair has excellent vision.
– The brown recluse spider has six equally-sized eyes in three pairs.
– Blind cellar spiders have vestigial eyes or lack eyes entirely.
– Some tarantulas like the starburst baboon tarantula have reduced eyes.
Arrangement of Spider Eyes
Having multiple pairs of eyes allows spiders to scan for prey, detect minute vibrations, and build mental maps of their surroundings. The positioning and types of their eyes reflect their preferred habitat and hunting methods:
Web builders: Spiders that build webs generally have very acute vision to pinpoint prey caught in their webs. Web builders like orb weavers and garden spiders have eight eyes, with the middle pair facing forward. The forward main eyes allow sharp focus on ensnared prey, while the peripheral eyes watch for flying insects.
Wandering hunters: Spiders that actively hunt without webs have their eyes spaced widely apart, providing keen peripheral vision to detect prey movement. Wolf spiders and jumping spiders have their eight eyes clustered into three rows on the front of their heads for detailed depth perception.
Burrowers: Spiders that live underground and emerge at night rely more on vibration cues than vision. Trapdoor spiders have eight very small, equal-sized eyes to simply differentiate light from dark. Their eyes lack sharp focus and mainly serve as early warning of threats.
No eyes: Blind cave-dwelling spiders have adapted to total darkness through loss of eyes. For instance, the Texas blind spider and blind cellar spiders either have vestigial non-functioning eyes or completely lack eyes. These eyeless spiders navigate via touch, vibration, and chemical signals.
Spider Eye Types
Spider eyes utilize two main types of visual cells:
Ocelli: Simple eyes called ocelli detect light, dark, and general movement. Each ocellus has a single lens and light-sensitive cells. They cannot form sharp images but are very light-sensitive. Most of the secondary eyes on spiders are ocelli.
Camera eyes: The main pair of forward-facing eyes are camera-type eyes called anterior-median eyes. These have a lens that focuses light onto a retina, allowing detailed daytime vision and color discrimination. The retina contains photoreceptor cells called rhabdomes that process images.
| Ocelli | Simple eyes, detect light/dark/motion |
| Camera eyes | Main eyes, sharper vision, color sensitivity |
| Rhabdomes | Photoreceptor cells in main eyes |
| Tapetum | Reflective layer, enhances light capture |
The camera eyes of most spiders also have a tapetum layer behind the retina. This reflective surface bounces light back through the photoreceptors, increasing light sensitivity for better night vision. This is why spiders’ eyes may glow when illuminated at night.
Do Male and Female Spiders Have Different Eyes?
Male and female spiders tend to have similar eye configurations. Vision is equally important for hunting, navigation, and predator avoidance in both sexes.
However, researchers have found some subtle sex-specific differences:
– Male jumping spiders may have larger eyes to spot females from a distance.
– In orb weavers, males may have a slightly larger field of vision to detect females in periphery while moving.
– Male wolf spiders seem to have better low light sensitivity to find nocturnal females.
So male wandering spiders may benefit from enhanced visual capabilities to locate mates. In web-builders, both sexes rely heavily on vision for survival, leading to less divergence. But overall, the eye arrangement remains largely the same between male and female spiders.
Do All Spiderlings Have Full Eyesight?
Baby spiders emerge from eggs with their full complement of adult eyes already in place. The eyes are fully functional right away to spot food and threats. Spiderlings moult and grow larger as juveniles, but the number and position of their eyes stays consistent.
However, the visual acuity of spiderlings does take time to refine as they mature. For example:
– Jumping spider babies have reduced depth perception compared to adults. Their vision sharpens over successive moults.
– Orb weaver spiderlings take a few moults for their eyes to reach maximum resolution. Their lens and retina develop as they grow.
– Wolf spiderlings have blurred night vision that improves gradually with each moult. The tapetum area expands as they get larger.
So while spider babies aren’t blind, their eyesight does sharpen up as they approach adulthood with each moult. The eyes attained right after hatching serve them well for basic functions, but fine-tuning takes time.
Do Spiders Blink or Clean Their Eyes?
Spiders do not blink or close their eyes like humans do. Spiders lack eyelids and tear ducts, so their eyes remain open continuously. But spiders do have other ways to maintain and clean their eyes:
– Transparent molting fluid rinses eyes when shedding their exoskeleton.
– Leg hairs and pedipalps brush dust and debris off the surface of the eyes.
– Spider fangs secrete venom that contains antibiotic compounds to disinfect their eyes.
– Fluids from the mouth and anus hydrate and wipe eyes clean.
While it may seem unsanitary to clean eyes with mouth and anal secretions, this is an effective mechanism in spiders. Their antibiotic venom also prevents infection from contact with these fluids.
Do Spiders Have Good Vision?
Most spiders have quite good vision within the constraints of their small body sizes:
– Excellent motion detection – their multiple retinas give a wide field of view and fast response to movements.
– Keen sensitivity in low light – their tapetum reflects back light through photoreceptors. Some spiders are active at night and can navigate using dim residual light.
– Detailed resolution with camera-type eyes – while not nearly as sharp as human sight, their forward eyes allow good visual discrimination, especially in web builders that rely on sight to capture prey.
– Color vision – at least in the camera eyes. Studies show spiders can distinguish colors and use them in discrimination tasks.
So spiders effectively use their sets of eyes for orientation, prey capture, mating, and threat avoidance. Their vision suits their ecological roles, even if image resolution falls short of human eyes. Exceptions are burrowing spiders that rely more on non-visual senses.
Do Spiders Always Have Eight Eyes?
No, not all spiders have exactly eight eyes. While eight is the ancestral state and most common eye number, some spiders have reduced eyes or lack eyes entirely:
– Blind spiders like the Texas blind spider have only vestigial eye tubercles without function.
– The liphistiid trapdoor spider has only four primitive eyes. Other trapdoor species have reduced vision.
– Tarantulas may have six eyes, or eyes of differing sizes. The starburst baboon tarantula has very small vestigial eyes.
– In some spiders, males may have eight eyes while females have six (odoratapor spiders).
– Jumping spiders have only six forward-facing camera eyes that confer excellent vision.
So the majority of spiders have eight eyes as an adaptation to detect prey and avoid threats. But in species that rely on other senses and live in total darkness, eyes may be reduced or lost.
Conclusion
Most spiders have eight eyes as an ancestral adaptation to their predatory lifestyle. Multiple pairs of eyes give spiders excellent motion detection, low light vision, and a wide visual field to spot prey and threats. Different types of eyes including camera eyes, ocelli, and tapetum enhance vision. Eye configurations vary between species based on hunting methods and preferred habitat. While eight eyes are standard, some spiders have fewer or lack eyes entirely if dwelling in complete darkness. Eyesight plays a critical role in most spiders’ survival, but is not universal.