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Английский язык
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conradmorrow995
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Геометрия3 минуты назад
Срочно прошу помочь с геометрией 10 класс!
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Русский язык33 минут назад
Ту где-то подвох, мыслей чую… Где логически-громматическая ошибка, кстати, я её уже нашёл.
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Алгебра33 минут назад
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Quoting an earlier comment of mine:
Spiders have the full gamut of vision, really! There are some species that live in dark caves and have lost their eyes entirely. They look really freaky. Just a smooth head where the eyes should be.
Many spiders that use webs to capture prey — like this orbweaver — have rather poor vision (see «Ecology») and sense the world primarily through vibration.
Other spiders, mostly active hunters like wolf spiders and jumping spiders, have large, forward-facing eyes with very sharp vision, as well as smaller eyes all around their head that track movement. Relative to its size, a jumping spider’s vision is about as sharp as a pigeon’s. Many visual spiders’ courtships involve dancing and colourful, high-contrast displays, and some can see into the ultraviolet as well.
At the extreme end of the scale, net-casting spiders’ massive front eyes, which they use to detect insects passing under them at night, are so sensitive that the retinas burn away in daylight and are regenerated by evening. If they ever turned their eyes to the stars, they would be able to see the Andromeda galaxy (speculation I pulled out of my ass based on their superior night vision).
Most spiders have 6 or 8 eyes; some have 2; some have 0. Boringly, the answer to «why 8 eyes» is probably «because they are all descended from animals with 8 eyes and it was never worth changing much». Evolution is essentially like doing repairs on an airplane while it is flying, and so if it ain’t broke, it don’t get fixed.
Spiders are famously known for having eight legs (sorry for reminding you), but did you know what else they have eight of? Eyes! Why would one animal need this many eyes? Well, all of these extra eyes actually serve their own unique purpose…
The Better to See You With, My Dear
Many different species of spiders, especially jumping spiders, have four sets of eyes. They need these extra sets of eyes, as they do not easily catch their prey in webs — they hunt! These spiders will use their main eyes for basic vision (with sharp, colored vision that allows them to see ultraviolet light that humans cannot see). The other eyes assist in enhancing their ability to react to catching their prey and defending themselves against predators.
The Purpose of Having Secondary Eyes
With the main eyes being used for basic vision, the secondary sets of eyes are believed to be used to detect motion. This will aid them in response to a predator attack or the movement of their prey. The most important set of eyes on spiders are the Anterior Lateral Eyes (ALE). This set is the next pair of eyes after the principal eyes. They are forward facing, but are used mainly for this motion detection. Without this set of eyes, the spider would be in some serious trouble…
What Happens Without the Anterior Lateral Eyes?
When the ALE eyes are damaged (or covered during tests), spiders are usually unable to react to quick changes that would require them to defend or attack. Even with the principal eyes being as sharp as they are, the ALE eyes are completely in charge of detecting motion. To stress how important these eyes are — a spider with blocked out principle eyes would be far better off than a spider with blocked off ALE eyes.
Spiders have eight eyes for survival — they’re not just something to freak us out when we see them crawling through our homes. If you have a spider infestation (or any other infestation) taking over your home, give us a call and we’ll help you manage it!
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most Spiders have 8 eyes
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(Image credit: Elizabeth Jakob, University of Massachusetts, Amherst)
Is it their eight creepy-crawly legs or their eight beady eyes that make spiders a spooky Halloween staple? Either way, new research suggests all those extra pairs of spider peepers have their own roles to play in keeping the arachnids safe.
Jumping spiders, a group of spiders that actively hunts its prey rather than trapping it in webs, have four pairs of eyes (as do most spiders). A new study finds that while the center, or principal, pair of eyes is good at picking out details, one of the side pairs is crucial for warning spiders when something is coming their way.
This «looming response» is the equivalent of a human ducking and covering when a baseball flies toward his or her face. But humans rely on just one pair of eyes to both avoid the baseball and see the details of its stitching. Jumping spiders use four eyes for the same tasks.
«We see that division of labor within that visual system,» study research Skye Long, a doctoral student at the University of Massachusetts, Amherst, told LiveScience. «That’s pretty cool if you think about it, because we only have one pair of eyes.»
Scared spiders
There are more than 5,000 species of jumping spider, which Long described as the «big cats» of the arachnid world for their hunting abilities. The principal eyes of these spiders allow for sharp, color vision; the spiders can also see ultraviolet light, which is outside the spectrum of human vision, with their main eyes, Long said. [Gallery: Seriously Spooky Spiders]
The secondary eyes dotted around the spiders’ heads are thought to help them detect motion, Long said, but the pair right next to the central eyes, called the anterior lateral eyes, or ALE, seem to be able to discern some detail as well. It was this pair of eyes that Long and her colleagues were interested in studying.
The researchers captured wild Phidippus audax, a species of jumping spider, and dabbed pairs of their eyes with green and orange paint, the arachnid version of a blindfold. In 16 spiders, the researchers masked the principal eyes. In 14, they covered the anterior lateral pair. Another 16 were left paint-free. (After the experiment, the researchers peeled off the paint to restore full spider vision.)
The spiders were then put into an enclosure with an iPod touch. On the screen was a black dot. When the spider was looking toward the screen, the researchers pressed play, and the dot either expanded quickly (as if it coming toward the spider) or contracted (as if receding).
If the spider could detect the motion, it would respond by backing up rapidly, usually lifting up a couple of legs in a defensive posture. [See video of a skittering spider]
«It’s a very scared response,» Long said.
But spiders with their anterior lateral eyes blocked didn’t show this response, the researchers reported in the Oct. 16 issue of the journal Biology Letters.
Meanwhile, «spiders with their principal eyes blocked behave the same as spiders that don’t have any paint on their eyes at all,» Long said.
Eye-mazing Evolution
That means the secondary eyes are crucial for alerting the spider to dangerous motion, Long said. Spider eyes are a «really cool step in evolution,» she added; insects have compound eyes with multiple lenses, and some areas of those eyes have certain functions. Spiders, on the other hand, separate out visual functions across their heads.
«This is a different pathway that evolution has taken to allow a very small animal to have a very extensive visual system,» Long said.
The researchers now plan to continue investigating the roles of the secondary eyes. They’re developing a spider eye-tracker so they can expose the arachnids to videos and watch where their principal eyes look.
«That gets us very deeply into how the spider is seeing the world,» Long said. «As close as it can get, really.»
Follow Stephanie Pappas on Twitter @sipappas or LiveScience @livescience. We’re also on Facebook & Google+.
Stephanie Pappas is a contributing writer for Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor’s degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz.