There are about 40,000 known spider species, and potentially thousands more we haven’t discovered yet. In their 400 million years of existence, they’ve spread over every continent and mastered nearly every environment on Earth. Whether you are afraid of spiders or not, you’ve got to admit that spiders are pretty impressive and well-equipped animals. Let’s take a look at the science behind what makes them some of the most successful carnivores in the world.
Have you ever wondered why spiders have so many eyes? It’s not just for looks. These creepy crawlers rely on their multiple eyes for a variety of reasons, from hunting prey to protecting themselves from danger. Keep reading to learn more about this fascinating topic!
Common number: 99% of spiders have eight eyes
As previously mentioned, spiders usually have eight eyes, which is the common number among 99% of species. Despite this, most spiders do not rely heavily on their eyesight for navigation. Instead, they use touch, vibration, and taste stimuli to understand their surroundings. However, while spiders may not use their main eyes for navigation, they still need them to detect basic vision. Interestingly enough, some spiders can also see ultraviolet light with sharper vision. So while the common number of eyes for spiders may be eight, their use and function play a significant role in how they navigate and survive in their environments.
Basic vision: Spiders use their main eyes for basic vision
Spiders may have eight eyes, but most don’t have good eyesight. Instead, they rely on touch, vibration, and taste stimuli to navigate. Spiders use their main eyes for basic vision, with sharp, colored vision that allows them to see ultraviolet light that humans cannot detect. Jumping spiders, for example, require keen vision for leaping and attacking insects. Their two primary, front-facing eyes offer high-resolution color vision, while their secondary eyes detect motion and provide depth perception. Spider eyes evolved to fit their way of life, and their large, forward-facing eyes help them judge distances and spot potential prey. Some of their largest eyes even point backward to keep a lookout for danger. While not all spiders have eight eyes, this common number serves an important purpose in their survival.
Ultraviolet vision: Spiders can see ultraviolet light using sharper vision
In addition to their basic vision, spiders have the unique ability to see ultraviolet light using their sharper visual perception. The principal eyes of jumping spiders, for instance, allow for sharp, color vision, including the ultraviolet spectrum, which is beyond the range of human vision. With their eight eyes, spiders can boast of better vision than humans on some counts. However, this doesn’t mean that all spiders have excellent vision, as many rely on their other senses such as touch, taste, and vibrations to navigate their surroundings. It’s interesting to note that evolution gave spiders such an array of eyes to help them adapt to their environment and challenges. Further, two of the eight eyes usually are large and face forward, and a couple of the largest eyes may point backward, allowing spiders to keep a lookout for danger. However, it’s worth noting that not all spiders have eight eyes; some species have six or four eyes depending on their specific needs.
Vibration detection: Spiders use touch and vibration to navigate
Spiders have eight eyes but they rely on touch, vibration, and taste stimuli to navigate rather than good eyesight. These arachnids use their vision as well as vibrations to sense movement and detect predators. Spiders also use their slit organs located near the joints to sense vibrations. They are able to change their stance and make their sense organs more receptive to particular frequencies of vibration simply by changing their position. Additionally, spiders use vibrations from the silk strands to locate prey and find deformities in the web. This unique evolutionary adaptation allows spiders to sense their surroundings and hunt with impressive accuracy.
Taste stimuli: Spiders use taste stimuli to sense their surroundings
In addition to their basic vision and ultraviolet detection abilities, spiders rely on taste stimuli to navigate their surroundings. Although their sense of taste is weak, spiders use their taste receptors to analyze their surroundings and detect potential prey or predators. This, coupled with their ability to perceive touch and vibrations, allows spiders to successfully hunt and survive in their habitat. These evolutionary adaptations have enabled spiders to fit into their unique way of life, and their eight eyes, including the large forward-facing ones, along with the backward-facing ones, serve as a tool for detecting danger and avoiding it. While not all spiders have eight eyes, it remains a common, intriguing feature of a majority of these eight-legged creatures.
Evolutionary adaptation: Spider eyes evolved to fit their way of life
As mentioned earlier, spider eyes are not just random; they have evolved over time to fit the needs of spiders. The eight-eyes setup ensures that spiders have the best chance of detecting any nearby movement, even though their vision is not very sharp. Being able to sense vibrations, touch and taste stimuli, in combination with their vision, helps them navigate the world around them. With two large eyes facing forward to get clear and color images, and two more pairs of lower-resolution eyes on the sides of their head, spiders can monitor their surroundings carefully. This evolutionary adaptation has helped spiders develop a unique and efficient way of gathering and processing sensory information, which is necessary for their survival.
Dodging danger: Spiders need their secondary eyes to dodge when something comes their way
As previously mentioned, spiders have eight eyes, with two of them being large and facing forward. These eyes serve the purpose of basic vision and color perception. However, spiders also rely on their secondary eyes to dodge danger. These extra eyes allow them to detect when something is moving towards them, giving them enough time to react and jump out of the way. Spiders’ ability to dodge danger is crucial for their survival in the wild. Their evolutionary adaptation has allowed them to navigate their surroundings and avoid predators efficiently. Along with touch, vibration, and taste stimuli, spiders’ eyes play a vital role in sensing their environment. While not all spiders have eight eyes, those that do benefit from having extra sets of eyes to watch their back and dodge danger.
Eye size: Two of the eight eyes are usually large and face forward
When it comes to spider eyesight, two of the eight eyes usually stand out. These two eyes are typically the largest and face forward, providing the spider with a clear, colour image and the ability to judge distance. These primary eyes are crucial for spiders to navigate and locate their prey. They provide overlapping stereoscopic vision to the front, which is important for hunting and survival. Additionally, these large eyes don’t move, making them the perfect tool for spiders to track their prey. Other spiders may have different eye arrangements, with some having vestigial or no eyes at all, but for those with eyesight, these two large eyes are typically the most important.
Backward-pointing eyes: A couple of the largest eyes pointed backwards to keep a lookout
As mentioned, spiders typically have eight eyes, and two of them are usually larger and point forwards to aid in navigation and hunting. However, a couple of the other eyes can be quite interesting, as they are often the largest and point backwards. These backward-facing eyes serve an important purpose of keeping a lookout for any potential threats from behind. This evolutionary adaptation allows the spider to be aware of any danger, and able to react accordingly to stay safe. It’s fascinating to think about how the different types of spider eyes have evolved to fit their unique way of life, from their basic vision to their ability to detect ultraviolet light and vibration for navigation. It’s no wonder that spiders are such fascinating creatures.
Not all spiders have 8 eyes: Some species have six or four eyes.
While it may be common for spiders to have eight eyes, not all species follow this pattern. In fact, some spiders have as few as six or four eyes. This variation in eye number can be seen as an evolutionary adaptation to fit the spider’s way of life. For example, those spiders that live primarily in dark environments, such as caves, may have no eyes at all. On the other hand, those that rely on vibration detection or taste stimuli may have fewer eyes, with greater sensitivity in each. This variety in eye number and sensitivity highlights the incredible diversity of spiders and the unique adaptations that allow them to survive in their respective environments.
The Anatomy of a Spider
Even though they’re tiny, they still have organs, a circulatory system and even a skeleton. Except that they wear their skeletons on the outside instead of the inside and this is something called an exoskeleton. Spiders also have lungs. Now they have one of two types of lungs neither of which is like the human lung. Some spiders have something called book lungs and a book long has a stack of soft plates called lamellae and oxygen passes through the lamellae diffusing through the tissue and into the blood. Other spiders have trachea which are basically tiny breathing tubes that allow them to bring air straight into their bodies.
As you know, some spiders can be venomous and when dealing with the effect of spider venom on humans, there are really just two types. Some spider venom is neurotoxic meaning that it affects the human nervous system beyond the immediate site of the spider bite. The venom of the black widow spider is neurotoxic, thereby causing rigidity, cramp and paralysis of the sympathetic systems. Other spider venom can be necrotic and causes damage to the tissue surrounding the site of the bite. The recluse spiders, for example, have necrotic venom. The damage usually results in skin blisters, ulcers and blackening of the local tissues.
Spiders are famous for their intricate and varied forms of spider webs. Spider silk is a protein that’s formed as a liquid by silk glands and squeezed out of something called a spinneret like toothpaste being squeezed from a tube. The liquid thread hardens as it makes contact with the air and leaves the spinneret and some types of thread become stronger than steel proportionate to that size. Most of the silk threads in a spider web are actually multiple strands of fine silk lying one alongside the other. Spiders produced several types of silk from different types of spinning glands. One type of silk produced by virtually all spiders is the type used for wrapping their prey. Another type of silk is used to make their egg sack and yet another is a sticky type often used as part of the spiderweb.
Although spiders are generally known for these webs, that’s not the only way that they have of catching food. There are three other key methods that spiders use to capture their prey. Firstly, sedentary spiders living inside silk-lined burrows leap out to capture passing prey. Some normally active spiders lie in ambush on plants or tree bark, on the ground or hidden under stones. Other spiders, like hunter spiders, go in search of their prey using their eight eyes and incredibly sensitive body hairs to detect the slightest of movement in the environment around them.
The Eyes of a Spider
Most spiders have eight simple eyes which actually perform different tasks. The two main eyes of a spider each have a simple lens and a retina which is made of light-sensitive cells whose surfaces point towards the light as it enters the eye. Now these main eyes have a small field of vision with a very high resolution. They’re especially strong in jumping spiders. A spider’s secondary eyes also have a lens but the light-sensitive cells of these eyes point away from the light as do the similar cells in the human eye. The secondary eyes detect shadows and the difference between light and dark.
All spiders of course travel around their immediate territory on foot but did you know that some spiders have learned to fly between their webs? Yes, you heard that right. Flying spiders do exist! Certain species of spiders have learned to launch themselves into the air and glide to another location by releasing a strand of silk that catches the wind. This remarkable ability allows them to travel further and faster than walking and also avoids predators on the ground.
The Role of Spiders in the Ecosystem
Spiders play an essential role in the ecosystem, particularly as predators of other insects. By consuming other insects, spiders help to keep the populations of those insects under control. This, in turn, can help to prevent the spread of diseases that may be transmitted by insects.
Furthermore, spider silk has various practical applications. It is incredibly strong, yet lightweight, and is being studied for use in bulletproof vests, surgical sutures, and even artificial tendons. Additionally, the venom of certain spider species is being researched for potential medical applications, including pain relief and treatment for neurological disorders.
Despite their remarkable abilities and important role in the ecosystem, many people have a fear of spiders. Arachnophobia, or the fear of spiders, is a common phobia that affects millions of people worldwide. However, understanding the science behind spiders and their behavior can help to alleviate this fear.
In conclusion, spiders are remarkable creatures that have evolved over millions of years to become some of the most successful carnivores on Earth. Their ability to adapt to different environments and catch prey in various ways is truly remarkable. Although some people may fear spiders, it is important to understand their vital role in the ecosystem and the potential applications of spider silk and venom in medicine. Next time you see a spider, try to appreciate its remarkable abilities and the important role it plays in the ecosystem.