A Little Bit More
The jumping spiders, family Salticidae (sall-TIH-sih-dee) are highly adept specialists at stalking and capturing insects. Their vision probably surpasses all other invertebrates - they even outperform the wolf spiders in their apparent alertness. Almost all jumping spiders are small, rarely more than *" (13mm) in length. Their whole body is usually covered with a thick blanket of colored hair. Some species are even iridescent.
Jumping spiders' exceptional vision is possible because their largest eyes (spiders have 8) receive a sharp image from a distance as great as 10-12" (250-300mm) and can see rather well over even greater distances. Typically, they see their prey in the distance, creep slowly toward it until close enough to leap, and then pounce with great accuracy. Most jumping spiders live off the ground in vegetation. They leap from stem to stem with ease and are saved from falling by a dragline thread that keeps them secured to their point of origin. If they miss their prey and fall, they simply haul themselves back to their perch.
Jumping spiders do not spin webs but do build retreats of thick, white, slightly sticky silk in crevices on or near the ground. They retire to these retreats at night or on cold days and use them for molting and hibernation as well. Spiders have a wide range of predators, mostly invertebrate. Many insects turn the tables and prey upon spiders! Although spiders have many hazards in life, from fungi that gains a foothold in their bodies and kills them from within to cannibalistic spiders that may eat eggs, young or adults, they remain one of the most abundant groups of animals on the planet.
Activities
Spider Pounce
Objectives: experience the factors that are involved for a jumping spider to catch its prey in mid-air
Materials: soccer ball (or similar) and space for about a 24 foot diameter circle
Take a little time to think about a jumping spider's ability to leap out into space and catch its prey as it flies by and you may begin to realize just how accomplished a feat this really is! A jumping spider must judge distance to the prey, judge the prey's speed, and judge its own jumping speed to make the mid-air contact possible. It's not unlike passing a ball to someone who is moving - you must make several judgement decisions to make contact with a moving recipient.
Here's an activity you can try that may help you understand what's involved for a spider to accomplish a mid-air capture. A soccer ball works well and you'll need enough space to separate two people by about 12 feet - one (prey) needs to be able to walk in a circle 12 feet distant from the person (spider) in the middle. Have an individual (jumping spider) hold the ball at some central location and another individual (prey) stand about 12 feet away. Have the "prey" walk in a circular pattern around the "spider" at a steady pace. The spider's goal is to toss the ball, underhanded, to the moving prey without making the prey do any more than easily, reach up and grab the ball. Remember, the prey needs to move at a steady pace in a circle as the spider tosses the ball to it.
You'll quickly realize that it takes several attempts to coordinate this well. It should become obvious after a few tries that the spider needs to "lead" the prey to insure that the ball arrives at the right place at the right time. Quarterbacks in football become very good at leading their receivers and regularly pass the football to a point where the receiver WILL be rather than where the receiver is at the time of the release.
People who have played sports using a ball may find this exercise much easier than others to accomplish. In fact, it might be interesting to note the number of attempts "more experienced" people make compared with those who are "less experienced". You can adjust this exercise by having the "prey" circle more quickly or more slowly.
Key Concepts
Behavior and Regulation, Identification, Predator/Prey Relationships, Structures and Functions
Questions
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Posted by Alfred Comeau on May 30, 2006 at 12:24 PM
Q: How can we eliminate these spiders and how harmful are they to humans and domestic household pets? The photo "BUNGEE JUMPER" seems to identify the spider accurately.
A: If your spiders are the same as or similar to those in the "Bungee Jumper" unit, you have absolutely nothing to worry about. Jumping spiders are totally harmless and will not harm you, your children or your pets. They will however, play havoc with insects! Jumping spiders move about looking for insects to catch and eat and will avoid humans whenever possible. These spiders may live more than one year so I suppose they may grow a bit over time but won't get very large. Keep in mind that there are many different species of jumping spiders so maybe you have several kinds on your porch.
I can understand that people get very worried about spiders if they aren't sure they're safe, but there really isn't any reason for you to fear them. Actually, jumping spiders have especially good eyesight and if you get close to them, they'll often look right up at you - they're really cute. If you allow these spiders to live on your porch, you'll have fewer insects to deal with all summer. My best to you and your family.
Posted by Rebecca Porter on September 17, 2005 at 06:58 PM
Q: I live in Alaska on the Kenai Peninsula, and as we don't have as many spiders as other places, I am curious as to whether all spiders molt, or which ones in Alaska would? I am living near Homer, AK. and I have found a lot of spider carcasses left behind, and am just curious. Thanks.
A: Good observation on your part. Yes, spiders all molt - it's the only way they can grow.
Unlike many insects, spiders don't go through egg/larva/pupa/adult stages but begin life looking very much like the adult form and then simple grow larger. Since they have an exoskeleton, they must shed the outer covering and expand their body before the new exoskeleton hardens. I'm sure many people see the shed skins of spiders and just assume that they're seeing a "dead" spider.
Thanks for asking.