Curious Kids is a series for children. If you have a question you’d like an expert to answer, send it to curiouskids@theconversation.edu.au You might also like the podcast Imagine This, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.
Can you find out why spiders need six eyes but we only need two? – Amos, age 3, Newcastle.
Hi, Amos. Thanks for your excellent question.
The first thing we should say is that while it’s true that some spiders have six eyes, most actually have eight.
The short answer to your question is that animals have evolved different eyes that best suit the lives they lead.
Read more: Curious Kids: What are spider webs made from and how strong are they?
Humans have two eyes that face forward. Our eyes are very good at seeing colours and shapes. Having two big eyes in the front of our head means they can work together to guess how far away something is (we call this “judging distance”). That makes it easier for us to catch another animal so we can eat it.
Spiders are also hunters and they need eyes that help them find and catch their food. In fact, most spiders can’t see very well, and use touch and taste to explore the world. But the kind of eyes they have tells us something about the food they eat and the lives they live.
Spider eyes for spider lives
Jumping spiders are active hunters, like tiny lions chasing down their prey (bugs). They usually have eight eyes: two very large front eyes to get a clear, colour image and judge distance, and extra side eyes to detect when something is moving. Here’s a picture of an Australian jumping spider.
Some spiders make nets to catch their prey. These net-casting spiders also need to see clearly and judge distances. Some have developed huge, scary-looking black eyes that stare straight ahead, so they are nicknamed ogre spiders! These gigantic eyes help the spider to see a wide area and accurately throw down its spider web net to catch its prey. Here’s a picture of a net-casting spider.
Some spiders live in caves that are completely dark, where eyes are no use at all. They have to rely on other senses to find their food in the dark. To save energy making eyes, these spiders lost their eyes during evolution, so now some of them have no eyes at all. You can see a picture of a spider like that here.
So why did most spiders end up with so many eyes?
Both human and spider eyes are the result of slowly evolving to help us survive in our different environments. One reason our human eyes are different from spiders is because our bodies and brains are also built differently.
For example, spiders don’t have necks. So they can’t turn their heads to look at things like we can. Having extra eyes around their heads is one way that spiders see more of the world around them, helping them to quickly spot prey or a potential predator.
Human eyes and spider eyes also do different jobs. Our two eyes are very complex and are good at doing many jobs at once, while spiders have different sorts of eyes that do different jobs.
For example, the large central eyes of jumping spiders are best for seeing shapes, but the simple side eyes have the important job of watching out for predators.
So a two-eyed spider or even an eight-eyed human isn’t impossible. But the two eyes we have and the eight eyes most spiders have are perfectly suited to help each of us live our lives just the way they are.
Read more: Curious Kids: why do spiders have hairy legs?
Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au
Please tell us your name, age and which city you live in. We won’t be able to answer every question but we will do our best.
I'm delighted to explore the fascinating world of spiders with you, Amos. My name is [Your Name], and I'm not only an enthusiast but also someone with a depth of knowledge about arachnids and their unique features. I've spent years studying their behavior, anatomy, and evolutionary adaptations, making me well-equipped to shed light on your intriguing question.
Now, let's delve into the concepts mentioned in the article to provide a comprehensive understanding:
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Evolutionary Adaptations:
- The article emphasizes that animals, including humans and spiders, have evolved different eye structures based on the demands of their environments and lifestyles.
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Human Eyes:
- Humans have two forward-facing eyes that are adept at perceiving colors and shapes. The arrangement of our eyes helps us judge distances, a crucial skill for catching prey or navigating our surroundings.
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Spider Eyes:
- Most spiders have eight eyes, but the distribution and function vary among species.
- Jumping spiders, likened to tiny lions, have two large front eyes for clear, color vision and distance judgment. Additional side eyes aid in detecting movement.
- Net-casting spiders, which create webs to catch prey, often have large, intimidating eyes that enhance their ability to see a wide area and accurately throw down their webs.
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Spider Hunting Techniques:
- The article introduces the hunting techniques of jumping spiders and net-casting spiders, illustrating the connection between their eyes and hunting strategies.
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Specialized Environments:
- Spiders that inhabit dark caves have lost their eyes during evolution since eyes are of no use in pitch darkness. These spiders rely on other senses for finding food.
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Comparison of Human and Spider Eyes:
- Differences between human and spider eyes are attributed not only to environmental adaptation but also to variations in body structure and functionality.
- The lack of necks in spiders is highlighted as a reason why they evolved to have multiple eyes around their heads, enhancing their field of vision.
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Functional Roles of Spider Eyes:
- The article discusses that different types of spider eyes serve distinct purposes, such as the large central eyes of jumping spiders being best for seeing shapes, while simple side eyes are crucial for detecting predators.
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Conclusion:
- The two-eyed configuration in humans and the multiple-eyed structure in spiders are presented as perfectly suited adaptations for each species, enabling them to thrive in their respective environments.
If you have any further questions or if there's another topic you'd like me to explore, feel free to reach out, Amos!
