The Everyday Animal: spider

Adorable jumping spider.
picture by Kenneth Gilpin at lookingcloser.net

Alright, maybe you're not a spider person. But looking into the big eyes of jumping spider, I find it difficult not to coo. This adorable spider has big eyes, a fuzzy body, comes in a unbelievable variety of forms and colors, and is quite the performer to boot.

But lets start with those big glassy eyes. All eight of them.

The two big ones in front that give jumping spiders their signature look are unique. They give the jumping spider incredibly resolution, beyond the ability of all other spiders and insects, and even as good as some vertebrates [1]. But such accurate vision comes at the cost of a debilitatingly narrow view. The other six eyes give a much wider view, but bad resolution, a poor substitute for catching prey that is just out of the peripheries.

Many vertebrates have a similar problem which they have usually solved by simply moving their eyeballs, but a jumping spiders' lenses are attached directly to the body, they can't move around. So they have evolved one better, moving the retina itself. Like a camera filming through a window, the retina moves inside the lens. This gives the jumping spider peculiar, color changing eyes; when the retina, the darkest part of the eye, is looking away from you, you can almost see through the lens, making it look colorful. And when the eye is completely black, the spider is looking right back at you [2].

That vision is especially important for the jumping spiders' signature hunting method: jumping. They are able to jump up to 40x their own length, an ability that would let me jump well over 200 feet (is Spider-Man starting to make a bit more sense now?) [3]. Unlike many other spiders, jumping spiders don't spin webs to catch prey, but actively stalk them on the ground instead [4].

The stalking techniques are incredibly complex. Jumping spiders often do not use a straight line to get to their prey as you might expect, but rather circle around, approaching it from a different angle. The problem is that such a rout can take the prey out of sight, and for many invertebrate hunters, that means out of mind [4]. But jumping spiders seem to go far beyond that, able to choose the best path even when it means they may never see their meal again until they get right-on-top of it [5].

Just some of the bright displays that these spiders exhibit.
photo from www.bio.sdsu.edu/pub/spiders/NewFiles/framespg.html

There is more to a jumping spider than just his aggressive side, they are also famed romantics. Male jumping spiders come in a wide variety of bright colors for attracting mates. The peacocks of the arachnid world, jumping spiders come in an astonishing variety of turquoise, maroons, yellows and oranges. The unique coloration can be used to brightly display, or in some cases, deceive [4].

Some species have evolved to become incredible mimics of insects such as ants, beetles and wasps. These disguises help protect them from birds, and other searching predators. Disguises can work both ways however, and some insects have evolved to look like jumping spiders, causing the other-wise hunting spider to back off [4].

No that is not an ant.
photo by Wayne Maddison
Used form the Tree of Life Web Project

But female jumping spiders seem to be particularly picky, and it takes more than just bright colors and disguises to woo them. So males, colors flaring, become tiny flamingo dancers, showing females a variety of dancing moves to show off their prowess. And their dancing repertoire is considerable, including running jumps, body sways and all kinds of leg movements [4]. And to take it one step further, the dance is choreographed to a song all their own.

Jumping spiders may not have ears, but, like Beethoven, they make and hear music by feeling vibrations. Using their abdomen, the males grind away, creating a series of impressive beats while they are dancing. They then put the two separate actions together, making quite the show, all in the name of spider love [1].

Sources:

[1] http://www.youtube.com/watch?v=sMa9FdNM5io
[2] http://www.tolweb.org/accessory/Jumping_Spider_Vision?acc_id=1946
[3] http://www.everythingabout.net/articles/biology/animals/arthropods/arachnids/spiders/jumping_spider/
[4] http://www.peckhamia.com/hosted/Richman%20Jackson%201992%20A%20review%20of%20the%20ethology%20of%20jumping%20spiders.pdf
[5] http://www.sciencedirect.com/science/article/pii/S0003347296903723

There is also sooo much more I wasn't able to cover so please check out:

Photo sources:

For the weekend before Valentine’s Day it seemed morbidly appropriate to do a post about the classic model of a bad relationship. Though they may strike fear into many of our hearts, they really are amazing creatures and have been given a largely unfair reputation as dangerous pests.

The main reason for this reputation is that black widows are one of only two venomous spiders in North America, the other being the brown recluse. While black widows have a tremendous amount of neurotoxin venom that they can inject, they very rarely if ever inject more than a small amount. This small amount is still dangerous, and immediate medical attention should be sought after being bitten, however, death very rarely occurs.

It has long been believed that black widow females, which are recognizably large black shiny, ate their mates immediately after mating. As it turns out, this is a widely believed myth. While this occurs occasionally true, it is far from a sure thing, and the majority of the time the males get away unharmed. But before all you male spiders out there breathe a sigh of relief, be aware that the life of a male black widow is still far from easy. Males are brown, small, rather plain looking and lack the dangerous venom of the females. As adults males never eat, but instead spend their entire nomadic life looking for females to mate with. So if you are alone this holiday, at least you can take solace in knowing you are not a male black widow.

Although the myth of cannibalism after mating is largely false, black widows are far from unfamiliar with cannibalism. Every summer, black widows can produce 4-9 egg sacs each containing 100-900 eggs (many sources had vastly different numbers, even for the same species). Of all of these babies, only about 1-12 survive, and why? Not because of predators, lack of food, but cannibalism! Yes, once hatched, within about 20 days all of the hundred(s) of eggs begin eating each other. This is done so that the few left will be much stronger, bigger, and well fed than they might be otherwise, better ensuring their survival. Still… so macabre (thank you word-a-day calendar).