Arthropods 1a

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Southern California Arthropods (Mostly) #1: Spiders 1
© W.P. Armstrong 15 April 2009
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Jumping Spider Family (Salticidae)

Male red jumping spider (Phidippus johnsoni) with enormous chelicerae and fangs.

Close-up view of eyes, chelicerae and fangs of a male red jumping spider (Phidippus johnsoni). Photographed with a hand-held Sony T-9 digital camera using fluorescent photoflood lamps. This entire image is about 5 mm across.

Red jumping spider (Phidippus johnsoni) on Gazania rigens var. leucolaena.

A red jumping spider, probably (Phidippus johnsoni).

Another jumping spider that superficially resembles an ant.


Orb Weaver Family (Araneidae)

The black & yellow argiope (Argiope aurantia).

The black and yellow argiope is one of the most colorful orb weaver spiders in gardens of southern California. The female is characterized by its large size (body often over 2.5 cm in length) and black abdomen with broad yellow bars along the sides. The spider typically hangs upside-down (head down) in its strong orb web. Below the center is a zigzag band of silk (called the stabilmentum) which may help to camouflage the spider in its web. This species (and others) are sometimes called "writing spiders" because the stabilmentum superficially resembles writing or letters of the English alphabet. The following orb weaver spider does not have a stabilmentum in its web.

The banded argiope (Argiope trifasciata) in Escondido, California.

A large banded argiope (Argiope trifasciata) photographed on Owens Peak north of Palomar College.

The Silver Argiope
(Argiope argentata).

Family Araneidae

Dorsal and ventral views of silver argiope (Argiope argentata) on the bluffs at Dana Point, Calif.

Silver argiope (Argiope argentata). Photographed 1 January 2009 in San Marcos, California.

See More Images Of The Silver Argiope
  Unusual Egg Case Of The Silver Argiope  


Orb Weavers Of The Genus Neoscona

Orb weaver spider (Neoscona oaxacensis) in Calabasas, California.


Orb Weavers Of The Genus Araneus

  See More Images Of Araneus and Neoscona Spiders  
See Cross Orb Weaver in Vancouver, British Columbia
Shamrock Spider At Prairie Creek Redwoods State Park

Orb weaver (Araneus gemma) at Huntington Botanical Garden.


Dew-covered web of an orb weaver spider.

  More Images Of Orb Weaver Webs (1)  
  More Images Of Orb Weaver Webs (2)  

Large female orb weaver. Originally thought to be Araneus; however, it lacks the characteristic paired dorsal bumps on anterior of abdomen. This may be the genus Neoscoma, possibly N. crucifera.

Male and female orb weaver spiders underneath the eaves of a tool shed. Photo taken in late afternoon, before the female constructs her evening web.

Close-up view of the "face" of a male orb weaver spider showing multiple eyes and two pedipalps (red arrows). The male deposits a drop of sperm on a special web, then sucks it into the pedipalps. In mating, the sperm is transferred by inserting a pedipalp into an opening on the underside of the female's abdomen.

  More Images Of Araneus & Neoscoma  


Orb Weaver Of The Genus Metepeira

The following orb weaver was photographed on a rosemary bush (Rosmarinus officinalis) in San Marcos. The web consists of both an orb web and an irregular web. The retreat is a tangled, knotted web made with debris and leaves woven into the silk, placed so as to make a small protective tent for the spider. When disturbed it quickly drops out of the leaf cluster retreat and returns when the danger has passed. The genus was identified by Jim Berrian of the San Diego Natural History Museum.


Unknown Spider In San Marcos, California

Unknown species of orb spider? Discovered in San Marcos, CA (1 Aug 2013).


Trashline Spider (Cyclosa turbinata) On A Fig Tree

The emerging female fig wasp faces many dangers after she leaves the safety of her protective syconium. One of these dangers during wasp exodus from summer profichi and fall mammoni crops of syconia are predators, including opportunistic spiders. The following three images show a minute orb weaver called the trashline spider (Cyclosa turbinata) that has built its web near a mammoni syconium of Ficus pseudocarica. On September 14, many wasps leaving the syconium fluttered into the web and were quicky caught by the tiny spider. They were immediately rolled into balls of silk and stored in a vertical row in the center of the web.

The minute orb weaver spider (family Araneidae) in the above four images is only about 5 mm long. It is called the trashline spider (Cyclosa turbinata) because it stores it victims, each rolled in cases of silk, in a vertical row in the center of the web.


Long-Jawed Orb Weaver Family (Tetragnathidae)

  Images Of Long-Jawed Orb Weaver In San Diego County  


Comb-Footed Spider Family (Theridiidae)

The black widow (Latrodectus mactans = L. hesperus) is one of the most poisonous spiders in North America. The neurotoxic protein latrotoxin is produced in glands of the cephalothorax and is injected through hollow fangs (chelicerae). Although the mechanism is very complex, alpha-latrotoxin apparently interferes with the normal flow of calcium ions across nerve cell membranes, thus effecting muscular contractions. Latrotoxin is an activator of synaptosomal calcium uptake, while conotoxin from the cone snail (Conus) is an inhibitor of calcium channels, yet both deadly toxins ultimately produce cramping or rigid paralysis. Latrotoxin is more toxic than most snake bites with a lethal dosage (LD-50) of 0.9 mg/kg in mice. [LD-50 is the dosage required to kill 50% of the experimental animals.] If you live in southern California, there is probably one of these spiders near or under your house at this very moment. Chilean scientists have been researching latrotoxin as a treatment for erectile dysfunction coupled with temporary infertility (contraseption).

Black widows (Latrodectus mactans = L. hesperus). They were photographed in a composter with Sony T-1 and T-9 digital cameras. The camera was held with one hand and extended at arm's length into the spider's web.

Facial view of a black widow (Latrodectus mactans) showing multiple eyes, large chelicerae and fangs. Photographed with a hand-held Sony T-9 digital camera.


Black Widow Juvenile Female (Presumably Latrodectus mactans)

Based on the size of pedipalps, this appears to be a juvenile female black widow, probably Latrodectus mactans.


Other Spiders In The Genus Latrodectus

The Australian Redback (Latrodectus hasselti)

Australian redback spider (Latrodectus hasselti) photographed by Stephanie Mifflin.

  See Wayne's Word Article On Sexual Suicide  


The Brown Widow (Latrodectus geometricus)

The brown widow (Latrodectus geometricus) is reportedly native to South Africa, although it was first described from South America. During the early 2000s it became well-established in urban Los Angeles and San Diego, particularly the coastal cities of San Diego County. The upper abdomen is mottled tan-brown to gray, often with reddish-orange spots and whitish patterns or geometric designs. In fact, some specimens superficially resemble immature black widows (L. mactans). The legs are often banded in black and yellowish-tan. The hourglass marking on the ventral side of the abdomen is more orange-colored than the black widow. This marking clearly separates it from the harmless false widow (Steatoda grossa) that commonly inhabits houses and garages in southern California). The egg sac is very distinctive and unmistakable. It is covered with pointed protuberances, unlike the smooth sac of the black widow. The sac contain about 80 eggs compared with 300 for the black widow; however, brown widows produce many more egg sacs during their life cycle and consequently many more offspring. In fact their higher fecundity may be one of the reasons why they are displacing black widows in areas where both spiders occur.

Some authorities state that brown widow venom is more potent than the black widow; however, it injects about half as much venom. According to Richard S. Vetter, Department of Entomology, University of California Riverside (2009), the brown widow is less dangerous than our local native black widow. Since both species occupy the same ecological niche, the brown widow may eventually replace the black widow in some areas.

Brown widow (Latrodectus geometricus).

Microscopic facial view of a brown widow (Latrodectus geometricus) showing multiple eyes and large jaws (chelicerae) tipped with fangs. Two of the large front eyes glowed orange when illuminated under the stereomicroscope.

Nikon D-90 with 60mm Micro-Nikkor AF-S F/2.8G ED Macro Lens: ISO 800, 1/80 F-32 (No Flash)

Sony T-9 with built-in flash: ISO 80, 1/60 F-5.6

Brown widow (Latrodectus geometricus) showing colorful geometric patterns on dorsal side of abdomen.

Sony T-9 with built-in flash: ISO 80, 1/60 F-5.6

Brown widow (Latrodectus geometricus) showing dorsal (left) and ventral (right) side of abdomen.


The False Widow (Steatoda grossa)

False widow (Steatoda grossa), a common house spider in southern California that superficially resembles the black widow. It lacks the characteristic red hourglass marking of the black widow and has a purplish-brown abdomen. Unlike its black widow cousin, this is a beneficial, non-poisonous spider that feeds on sow bugs. Unfortunately, it is often killed because it is mistaken for a black widow. According to Charles Hogue (Insects of the Los Angeles Basin, 1993), it reportedly preys on black widows.

References:

  1. Evans, A.V. 2007. Field Guide to Insects and Spiders of North America. Sterling Publishing Co., Inc. New York, New York.

  2. Evans, A.V. and J.N. Hogue. 2004. Introduction to California Beetles. University of California Press, Berkeley, California.

  3. Hogue, C.L. 1993. Insects of the Los Angeles Basin. Natural History Museum of Los Angeles County.

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