California Native Plant Society
in collaboration with East Bay Municipal Utility District
Spiders (details)
All writing by May Chen's Pollinator Post from Bringing Back the Natives website
A female Johnson’s Jumping Spider
Phidippus johnsoni (family Salticidae)
Also known as the Red-backed Jumping Spider, Phidippus johnsoni is one of the largest and most commonly encountered jumping spiders in western North America. Males have an all-red abdomen, while females have black and yellow markings on their abdomen. Salticids are free-roaming hunters. They do not weave a web to catch prey. They stalk, then pounce on their prey. Just before jumping, the spider fastens a safety line to the substrate. It can leap 10-20 times their body length to capture prey. Their movement is achieved by rapid changes in hydraulic pressure of the blood. Muscular contractions force fluids into the hind legs, which cause them to extend extremely quickly.
In the second photo, her hairy pedipalps partially covering her iridescent blue chelicerae, the spider has her anterior median eyes transfixed in front of her.
The pedipalps are jointed appendages, much like small legs. They are used by the spider to sense objects, shape their webs, and to aid in prey capture and feeding. In male spiders, the pedipalps are also used to deliver sperm during mating.
Jumping spiders have excellent vision, with among the highest acuities in invertebrates. The 8 eyes are grouped four on the face (the two big Anterior Median Eyes in the middle, and two smaller Anterior Lateral eyes to the side), and four on top of the carapace. The anterior median eyes provide high acuity but small field of view, while the other six eyes act like our peripheral vision, with lower resolution but broad field of view. Since all eight eyes are fixed in place and can’t pivot independently from the body like human eyes can, jumping spiders must turn to face whatever they want to see well. This includes moving their cephalothorax up and down, an endearing behavior.
Crab Spider-
Mecaphesa sp. (family Thomisidae)
Its powerful front legs flexed back, a tiny Crab Spider, Mecaphesa sp. (family Thomisidae) has stationed itself on a petal of a buttercup flower.
Members of the family Thomisidae do not spin webs, and are ambush predators. The two front legs are usually long and more robust than the rest of the legs. Their common name derives from their ability to move sideways or backwards like crabs. Most Crab Spiders sit on or beside flowers, where they grab visiting insects. Some species are able to change color over a period of some days, to match the flower on which they are sitting.
Mecaphesa asperata, the Northern Crab Spider is found in North and Central America, and the Caribbean. The ambush predator generally lurks in similarly colored flowers for visitors such as bees and flies. It is similar in appearance to the better-known Goldenrod Spider, Misumena vatia. Mecaphesa can be distinguished in that the carapace, abdomen and legs are covered with numerous short stiff spines.
It is often assumed that Crab Spiders change colors to blend in with their surrounding. The truth is a little more complicated than that.
The spider can change its color between white and yellow to match the flower it is sitting on. The color change takes a few days. Maybe this spider has recently moved over from a nearby yellow flower?
There’s another trick that the spider might be playing that we are not aware of because we cannot see in the ultraviolet (UV) spectrum of light. It’s been discovered that Crab Spiders reflect UV light strongly. Most insects, notably the bees, see UV well, and favor sunlit flowers while foraging. Experiments have shown that flowers that have crab spiders sitting on them actually garner more insect visits than those that don’t! It is thought that perhaps color camouflage in the visible spectrum helps the spiders avoid vertebrate predators (birds, lizards, etc.), while the UV reflectance is useful for attracting insect prey.
The Six-spotted Orbweaver
Araniella displicata (family Araneidae)
The Six-spotted Orbweaver, Araniella displicata (family Araneidae) is a small cucumber spider. It occurs throughout Europe and North America and in parts of Asia. It is found on trees and shrubs in woodland habitats. It is one of the most widely distributed arachnids in North America, but often overlooked due to its small size. Adult females measure only 4-8 mm in length, males 4-6 mm. The species is distinguished by three (sometimes four) pairs of black spots along the edges of the rear half of the abdomen. There’s quite a bit of color variation within the species. Most orb weavers spin fairly large webs in proportion to their own body size, but not so with Araniella displicata. The web of an adult spider may be only three or four inches in diameter. The spiral snare is usually built well off the ground, and often oriented in the horizontal plane, frequently spanning the edges of a single large leaf. The spider sits in the center, hanging beneath a horizontal web. Adult Araniella displicata are often mistaken for “baby” orb weavers. In late May or early June mating takes place, and females produce egg sacs that contain 80 eggs and are covered in loose, fluffy, yellowish silk. The package may be deposited in a curled leaf that also serves as the mother’s retreat on the perimeter of the web.