A few of the Common Spiders at BLP The following spider notes are specific to BLP, but may also be useful throughout coastal California. The best beginning book on spiders is Spiders and their kin by a Harvard professor and his wife, Herbert and Lorna Levi. The book is in the library and is available at the bookstore. The notes below often refer to that book by page number. These notes were slightly rewritten by Greg de Nevers from an earlier version by Mary Anne Saddler and Ann Christensen. They were further slightly modified by David Herlocker and subsequently modified by Gwen Heistand. GENERALITIES. Male spiders are generally smaller than females, and often more cryptic. Females have bigger abdomens (full of eggs). Mature males have a pair of enlarged palps that look like boxing gloves in front of their face, females never do. Virtually every web you see has a spider on or near it. Look for them! They often hide where a radial strut attaches to a plant near the top of the web. There are no records (specimens) of brown recluse spiders from the Bay Area. ORB WEAVERS. Orb weavers (a family – Araneidae – with many genera) are the classic spiders, like Charlotte, making a wagon-wheel shaped web. They are the most numerous and diverse group of spiders. With a life span of one year or less, they emerge from their egg sacs in spring as tiny spiderlings. They balloon away from their birthplace, grow through the summer, and lay eggs in the fall. Orb weavers are the only spiders known to write in English. There are many small, fascinating orb weavers at BLP. A few large, glamorous ones are described here. Garden Spiders (genus Argiope, pg. 68). There are two common garden spiders at ACR, the banded garden spider, (=silver garden spider, = Argiope trifasciata), and the golden garden spider (= yellow and black garden spider, = Argiope aurantia). Garden spiders hang head-down in the center of their orb webs, which have a vertical zigzag of extra silk woven in (the stabilimentum). The stabilimentum got its name from the theory that it provided extra support for the web. Now it’s thought that the range of light it reflects may attract insects (prey). Spend a little time looking at the web, and you can see that it is not precisely vertical, rather slightly tilted from vertical. This is so that when the spider drops, she can drop straight down and not get tangled in her own web. When a victim is caught in the web she speedily wraps it in silk and then inserts her fangs to kill it. The males are smaller, and can be seen in webs of their own, or on the outskirts of the female’s web. The male courts the female by plucking web strands in specific patterns. Essentially, he plays her a tactile “tune.” As many as seven males have been seen simultaneously in the web of one female. Many of us have learned that females kill and eat their mates once sperm transfer is complete. It turns out there’s something a little more dramatic going on in the sex life of our beloved yellow and black garden spider, Argiope aurantica. During spider sex male spiders insert sperm into the females using their pedipalps sequentially, one after the other. When the male A. aurantica uses his second palp, he “suffers irreversible seizure,” becoming completely motionless, his heart stopping altogether within 15 minutes. “The dead male’s inflated palp remains wedged inside the female. This prevents her from mating again, and gives his sperm crucial minutes to fertilize her eggs. The female cannot pull the male out for at least 15-25 minutes. Other males try hard to pull the dead male out, but often fail.” So he is turning himself into a copulatory plug or as the article says a living-soon-to-be- dead “chastity belt.” Pretty wild! The female will eventually eat her mate; however she is not responsible for his death. 1 This sliver banded garden spider (A. trifasciata) makes an egg case that has a flat top. The top when viewed from above often looks like a piece of leaf caught in the vegetation. The yellow and black garden Banded Garden Spider spider (A. aurantia) constructs a pear-shaped egg sac that turns a wonderful brown as it ages. Golden Garden Spider The construction of the egg case is really an amazing feat. Argiope aurantia constructs her egg sac while hanging downwards from her web. She lays a series of cross lines attached at several points to create a scaffold. Then she lays down yellowish threads to form a rectangular roof, and on this she spins a thick tuft of fluffy yellowish silk. Into this “feather bed” she spins a firmer sheet of dark brown silk and she lays her eggs upwards against this brown silk. The egg mass looks like a hanging yellow spherical ball. A. aurantia then spins a thin, tough covering that joins the brown silk disk. Around the whole mass (eggs, their covering, and the rectangular roof) she spins a fluffy covering, and over this padding a finer covering of silk that eventually dries, hardens, and turns a brownish color. (To summarize: 6 different sheets, tufts or covers, making three envelopes!). Pumpkin Spider or Shamrock Spider (genus Araneus, pg. 57). Araneus is a large genus of often-colorful spiders, which make a retreat off of the orb itself. The pumpkin spider (Araneus trifolium) builds a retreat off of the orb, a cup-shaped structure, opening down. She uses a separate radial line as a signal line, through which she can feel the vibrations of moving prey. Pumpkin spiders are usually orange, with white lines or bands on the legs. (Interestingly enough, the same species on the east coast is greenish and often referred to as the shamrock spider. We occasionally find greenish ones her as well.) In late fall she lays her eggs in a case of fluffy, white silk which darkens as it ages. There can be as many as 2,000 eggs in a single case. Debris spider (genus Cyclosa, pg. 63). Cyclosa is an orb weaver who makes a very finely meshed web. She sits in the center, but is wonderfully camouflaged in a vertical line of debris she weaves into the web. The debris consists of plant material, as well as dry prey items. (This debris line is also referred to as a stabilimentum.) The abdomen of our most common debris spider is distinctive, being conical leading to its name, Cyclosa conicum. (There are four species of Cyclosa in the Bay Area.) When she is ready to lay eggs they are added to the line of debris, much like the labyrinth spider below. Labyrinth Spider or Condo Spider (genus Metepeira, pg. 64). The labyrinth spider is one of the most prominent orb weavers at BLP. The webs of different individuals are often built in close proximity, even sharing support strands. Could these spiders be called semi-colonial? Large Ceanothus bushes may have as many as twenty labyrinth webs, each branch opening supporting one or more spiders. The web is distinctive, consisting of a typical orb, plus a tangle of irregular, dry strands above or to the side of the orb. The spider sits hidden in a retreat in the center of the tangle, with a line to the orb hub to sense prey. The retreat is usually made of a leaf rolled conically, open end down. The spider will shake the web to make her prey move in order to locate it. Condo spiders enclose their eggs in a sac that has the shape of a double convex lens (lenticular egg sacs). The first egg sac is formed near the entrance of the retreat and the others are placed successively in a 2 line below the first one and fastened to a strong cord of silk. There are usually 5-6 cocoons with about 30 eggs in each. The cord supporting the egg sac is stretched between two branches and is strengthened with additional draglines. The egg sacs can survive winter storms and will be held securely in place after all traces of the web have disappeared. (Although, some accounts say that the young spider hatchlings use the messy web portion as a nursery.) Long-jawed Spider, or Stream Spider, or Marsh Spider (genus Tetragnatha, pg. 71). The most prominent spider in marshy areas, and around the edges of ponds and streams is the long- jawed spider. She sits with six legs extended parallel to her body, often on a grass blade or reed. She holds on with her short third pair of legs, and blends into the vegetation. Her web is often horizontal or close to it, rather than the typical near-vertical orientation and is missing the central hub. The male has special spurs on his chelicerae. When courting, the male and female approach each other with jaws agape. Their front legs come in contact with each other and male pushes female’s legs apart and employs the special spurs on his jaws to lock into opposing spurs in her jaws … keeping her jaws out of commission and facilitating non-fatal sperm transfer. The trouble often comes when he leaps backwards to safety. This leap is not always successful. Zygiella (genus Zygiella, pg. 61). Zygiella webs are distinctive not for what they have, but for what they lack. The spider omits the spiral, sticky threads from one or two inter-strut spaces as she weaves her web, giving the impression of a pie with a slice or two eaten.