A Natural History of California by Allan A. Schoenherr

Author:Allan A. Schoenherr
Language: eng
Format: epub
ISBN: 9780520295117
Publisher: University of California Press

FIGURE 8.31 Silver-backed Garden Spider, Argiope argentata. Note small male to upper left (photograph by Lenny Vincent).

Cobweb Spiders (Family: Theridiidae) are very common small spiders with 32 known genera in North America. They make conspicuous webs around homes, rodent holes, rock piles, as well as tree cavities and branches. The most famous and the most feared is the Western Black Widow, Latrodectus hesperus, which is the only dangerously venomous spider likely to be encountered by a human in California. Its distinctive red hourglass pattern on the underside of its bulbous abdomen is its identifying characteristic. They are not likely to be encountered in natural habitats, but they are fairly common in urban settings where they may live in wood piles, old houses, or urban debris. Historically they were known to lurk in outhouses. There are five species of widow spiders in the United States. The only other one likely to be encountered in California is the Brown Widow, L. geometricus. It was first discovered in Los Angeles in 1999, and now it has been recorded in more than 30 cities in southern California, an amazing rate of dispersal. Much less dangerous than the Black Widow, it can still deliver a painful bite. Webs can be found easily at night in a variety of locations in suburban gardens hanging upside down with its hourglass clearly visible.

Of special interest among arthropods are the ticks and mites. Although they are more closely allied to spiders than to other arthropods, they are not predators in the typical sense of the word. Altogether, they occur in practically all habitats and rival insects in diversity. Ticks are bloodsuckers, and as such they are considered to be ectoparasites. Experienced hikers have long known the importance of checking themselves for ticks after a day in the chaparral. Recently, the spread of a tick-borne malady known as Lyme disease has made this practice even more important. Lyme disease is spread by the bite of the small Deer Tick, Ixodes pacificus. Symptoms of Lyme disease include a rash at the site of the bite, often target-shaped, which if left untreated is followed by an arthritis-like inflammation of joints and associated nausea and fever. The disease is caused by a bacterium, Borrelia burdorferi, and once the symptoms are recognized, it may be treated with antibiotics. The problem is that the symptoms may not show up for a month after the bite, by which time the victim may fail to associate the symptoms with the hike in the brush. Interestingly, the Western Fence Lizard is immune to Lyme disease, and its blood is being studied with the idea of developing a treatment for Lyme disease in humans.

Mites are very small versions of ticks. Many of them are scavengers, and a large number of them are ectoparasites on plants and animals. Close inspection of lizards in chaparral areas, for example, commonly reveals groups of small red mites clustered near the ears or in the armpits. Of recent interest is the discovery that the

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