Posts Tagged: jumping spider
Ophthalmologist and professor Ivan Schwab of the UC Davis Health System says that spiders “get a bad rap. Few would harm you, and only rarely are spiders aggressive towards humans. Most will defend themselves if threatened, of course, and a few are venomous. Most spiders, however, would prefer to ignore humans and be ignored by us.”
At his UC Davis Department of Entomology and Nematology seminar on Oct. 23 in Briggs Hall, Dr. Schwab told the crowd that jumping spiders have the “best acuity of all spiders.” They are ambush spiders, lying in wait for prey.
If you visit your garden or a neighborhood park, you may see a jumping spider looking back at you. Last Sunday we spotted a jumping spider lurking beneath the petals of a yellow rose. Meanwhile, a honey bee foraged above it.
That reminded us of what Dr. Schwab said about spiders and how they see.
Background: Dr. Schwab directs the Cornea and External Disease Service and serves as the medical advisor of the eye bank, as well as professor of ophthalmology in the Department of Ophthalmology and Vision Science. He’s the author of five books, including the highly acclaimed Evolution’s Witness: How Eyes Evolved, published in November 2011. He describes the eye as "evolution's greatest gift and its greatest triumph."
The UC Davis ophthalmologist writes an informative blog, Evolution’s Witness, and recently penned one, with amazing detail, on jumping spiders. “Jumping spiders are positively charming creatures, and you will know that to be true if you have ever watched one closely. These are common spiders and range from approximately 3 to 17 mm in length and will watch you closely as you approach them. They have four pairs of eyes, with the large anterior median (AM) set the most obvious. These circular eyes provide an ‘attentive child’ appearance because they are fixed and are relatively large based on body size, but are tiny on an absolute scale. These placid eyes belie the organized complexity and evolutionary genius that lies beneath the carapace.”
Dr. Schwab goes on to describe the AM eyes as "Galilean telescopes with a corneal lens fixed to the carapace, and a second 'lens' at the end of a small tube immediately in front of the retina."
"This compact telephoto lens system combined with the tiered retina," he says, "achieves excellent acuity, but only a very tiny field of vision. So, to increase this field of acute vision, this optical marvel moves the tube housing the retina with six muscles per eye by mostly scanning movements. This is akin to a raster scan similar to those seen on a TV or computer screen. Jumping spiders scan their world much like painting a wall with a fine brush although the retina is not linear, but shaped more like a boomerang. The other pairs of eyes do not scan and are principally used as motion detectors to find other animals for the AM eyes to decipher."
"With the AM eyes, jumping spiders have the finest discrimination of all arthropods, and probably all invertebrates as they are visual hunters, whereas most other spiders use the tools of silk."
Dr. Schwab marvels at how a jumping spider is able to see so well and ambush its prey. "If the spider moves, it may frighten the prey, so the spider needs another mechanism." Read Dr. Schwab's column for the details on that mechanism. After you do, you'll come away with a greater appreciation of jumping spiders and that most amazing organ, the eye.
By the way, this visual hunter (below) didn't nab the honey bee Sunday afternoon....but it may have later.
Jumping spider peering between the petals of a yellow rose. (Photo by Kathy Keatley Garvey)
Close-up of jumping spider as it emerges from its hiding place. (Photo by Kathy Keatley Garvey)
Side view of jumping spider. (Photo by Kathy Keatley Garvey)
The prey (honey bee) that the predator (jumping spider) was seeking. (Photo by Kathy Keatley Garvey)
There's a good reason why jumping spiders are named "jumping spiders."
A jumping spider, according to National Geographic, can jump 50 times its body length.
We saw this jumping spider (family, Salticidae and probably genus Phidippus) in our flower bed last weekend.
Perched on a pink petunia, it waited for dinner, its four pairs of eyes surveying the floral menu; its rear legs poised to jump; its front legs ready to grasp unsuspecting prey. Meanwhile, its iridescent chelicerae glistened in the sunlight.
Wikipedia says that "the genus name is likely derived from Cicero's speech speech Pro Rege Deiotaro (Speech in Behalf of King Deiotarus): Phidippus was a slave who was physician to King Deiotaros. Literally, the word means 'one who spares horses' in Ancient Greek."
One thing's for sure: A hungry Phidippus would not "spare" a bee! Check out this National Geographic video on You Tube about a jumping spider and a honey bee.
Jumping spider on a petunia. (Photo by Kathy Keatley Garvey)
Close-up of jumping spider. (Photo by Kathy Keatley Garvey)
It's a bug-eat-bug world out there.
Today we watched a syrphid fly, aka "hover fly" and "flower fly," circling a blanket flower (Gaillardia) and then touching down to sip a little nectar.
Syrphids are called "hover flies" for good reason. They "hover" over a blossom, helicoperlike. They're often mistaken for bees but to the trained eye, they really look nothing alike. Folks confuse them because both bees and syrphids are floral visitors and both are pollinators.
If it's a floral visitor, it must be a bee, right? Wrong.
Anyway, this syrphid touched down on the blossom to sip nectar, its wings glinting in the early morning sun. Finally, it spotted the danger, a jumping spider lurking on the other side. The crafty predator lunged. Missed!
When we returned a few minutes later, however, we saw the jumping spider beneath the petals, feasting on the syrphid.
Quickness is an attribute--whether you're a jumping spider or a syrphid.
If you want to learn more about flower flies, read entomologist Robert Bugg's "Flower Flies (Syrphidae) and Other Biological Control Agents for Aphids in Vegetable Crops" (Publication 8285, May 2008, University of California, Division of Agriculture and Natural Resources.)
Syrphid fly (right) circles a blanket flower, unaware of the jumping spider. (Photo by Kathy Keatley Garvey)
Syrphid fly sipping nectar close to the predator. (Photo by Kathy Keatley Garvey)
End result--the jumping spider feasting on the syrphid fly. (Photo by Kathy Keatley Garvey)
Jumping spiders have to eat, but do they have to snag the bees?
Last weekend as we were checking the lavender patch in our yard, we noticed something partially hidden--and moving--on a post.
It was a jumping spider eating a honey bee. Later in the afternoon, the same jumping spider snared a sweat bee.
If you have flower patches in your yard--and you should, to attract the pollinators--you will also attract the predators.
Fortunately, they don't eat as much as Joey "Jaws" Chestnut of San Jose, the hot-dog eating champion of the world.
Jumping spider eating a honey bee. (Photo by Kathy Keatley Garvey)
Jumping spider eating a sweat bee. (Photo by Kathy Keatley Garvey)
Moving fast, a spider heads for prey. (Photo by Kathy Keatley Garvey)
If you walk slowly into your garden or backyard, and observe your surroundings, you'll find them. A jumping spider perched on a rose leaf. A soldier beetle climbing out of a tulip. A syrphid fly, aka flower fly or hover fly, foraging on a poppy blossom.
The insects (and spiders!) are back. The springlike temperatures, accompanied by bursts of rain, mean that these tiny little critters are everywhere.
If you pop a macro lens on your single-lens reflex camera, or use the macro setting on your point-and-shoot camera, you'll get them. There's even a set of lenses (macro, wide-angle and telephoto) that magnetically attach to your I-phone camera.
Travelers say it's fun and educational to go to Africa on safari, but you can also go on a Bug Safari in your backyard. It won't cost nearly as much, you don't have to make reservations, you don't have to hire a tour guide, and you don't have to worry about a water buffalo charging you.
Or your credit card company charging you.
A jumping spider perched on a rose leaf. (Photo by Kathy Keatley Garvey)
A soldier beetle peers at the camera. (Photo by Kathy Keatley Garvey)
A syrphid or flower fly foraging on a poppy blossom. (Photo by Kathy Keatley Garvey)