Arthropods 1b

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Southern California Arthropods (Mostly) #1: Spiders 2
© W.P. Armstrong 15 April 2009
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Trapdoor Spider Family (Ctenizidae)

Nest of a trapdoor spider compared with U.S. penny (diameter 19 mm).

California trapdoor spider (Bothriocytum californicum) inside its nest.

The tubular burrow of a trapdoor spider may be six to ten inches deep (15 to 25 cm) with walls lined with a smooth, silken web. The entrance is capped with a very tight-fitting lid which is hinged on the uphill side. The spider holds the door shut with its chelicerae and then suddenly opens the door and grabs a hapless passerby. Trapdoor spiders prefer to build their nests on sunny, south-facing hillsides, preferably in adobe-type soils. Very few spiders are known to actually dig their nests in the ground. Unfortunately, the coastal sage scrub habitat in southern California where trapdoor spiders live is rapidly being converted into housing developments.

Male California trapdoor spider (Bothriocyrtum californicum) and its burrow.

Some Other Interesting Arthropods
See The Amazing Kissing Bug

Tarantula Family (Theraphosidae)

Large California tarantula (Aphonopelma sp.) from Twin Oaks Valley.

Close-up view of tarantula chelicerae (jaws) each tipped with a large hollow fang.

Enlarged view of the tip of a fang showing canal for injecting venom (white arrow). The
beveled tip and hollow core are remarkably similar to a hypodermic syringe (see inset).

Aphonopelma Molt & Urticating Hairs

In order to grow, tarantulas must shed their exoskeleton (molt). The exoskeleton is composed of chitin, a long-chain nitrogen-containing polysaccharide. It is similar to cellulose except one hydroxyl group on each monomer is replaced with an acetyl amine group. It is covered with several different types of hairs (bristles) that are very different from mammalian hairs. New World tarantulas of the family Theraphosidae have microscopic, easily detached, urticating hairs that are released from the abdomen (opisthosoma) in the face of danger. By briskly rubbing its abdomen with its hind legs a cloud of hairs are released in the direction of a would-be predator. If the barbed hairs pierce the skin or lodge in the cornea the results can be excruciating and debilitating.

Note: Finger nails, horn, mammalian hair, wool, claws, beaks, scales, and feathers are composed of keratin, a fibrous protein with a high percentage of the amino acid cystine. Unlike other proteins, including collagen of connective tissue, tendons and cartilage, keratin is resistant to hydrolysis by most solvents (including weak acids and bases), and by proteolytic enzymes of the gastrointestinal tract. The stability of keratin is due to numerous primary disulfide (-S-S-) cross-linkages within the molecule and secondary hydrogen bonding between neighboring polypeptide chains.

The following image shows an Aphonopelma molt and urticating hairs from a tarantula I rescued from Owens Peak near Palomar College. The hairs appear more "plumose" (a botanical term) than other urticating hair images I have observed on tarantula websites. The hairs are very minute and require at least 400x magnification with a compound microscope. Apparently the effects of Aphonopelma plumose hairs on humans are not as severe as the more harpoon-shaped, barbed bristles of other genera.

A recently deceased tarantula found on Owens Peak north of Palomar College.
I can't be sure that this tarantula was killed by a tarantula hawk wasp (Pepsis).

See Tarantula Hawk Wasp (Pepsis)

Brazilian white-knee tarantula (Acanthoscurria geniculata).

Cobweb or Cellar Spider Family (Pholcidae)

A cobweb spider (Pholcus phalangioides) in its web.

The cobweb spider (Pholcus phalangioides) is a common domestic spider introduced from Europe. It is the major contributor of unsightly cobwebs under the eaves of homes and in the ceilings of rooms. When disturbed, it gyrates in its web, presumably to scare away potential predators. In San Diego County, a graveyard of dead Argentine ants in the corner of a room is evidence of a cobweb spider perched high above on the ceiling. Cobweb spiders belong to the order Araneae along with most spiders. The true "daddy long-legs" or "harvestmen" belong to the order Opiliones. In southern California, our two common genera of harvestmen are Protolophus and Leuronychus. An insect that is incorrectly called a daddy long-legs is the common crane fly (Tipula planicornis)

See The Long-Legged Crane Fly

Ground Spider Family (Gnaphosidae)

This may be a parson spider (Herpyllus ecclesiasticus). The white stripe on abdomen supposedly resembles a cravat or ruffled neck tie worn be men of the clergy during 18th century. Its body was about 10 mm in length. These fast-running spiders are introduced from Europe and are very common in my house in San Marcos, CA.

Another fairly common nocturnal ground spider in my house. It is missing one hind leg. It is similar to on-line images of the genus Orodrassus.

Ant Mimics & Ground Sac Spiders (Family Corinnidae)

I originally thought this was another fast-running ground spider (family Gnaphosidae) on Owens Peak in San Marcos, CA. Now I think it is an ant mimic spider Castianeira occidens of the ant mimic & ground sac spider family Corinnidae.

Mimicry: One insect (called a mimic) that is perfectly palatable to its predator resembles another insect (called the model) that is quite disagreeable to the same predator. Mimicry in which the mimic is essentially defenseless is called Batesian Mimicry. A harmless moth (Aegeria) is a Batesian mimic because it is incapable of stinging another animal, but yet it resembles the yellow jacket wasp (Vespula). To a larger predator (preying mantis or bird) this small spider is essentially defenseless. If it resembles a powerful stinging insect like the red velvet ant (a wasp), the predator might be reluctant to grap it. The problem here is that it is not a very good mimic, at least in my humble opinion. Maybe this is an example of "Imperfect Batesian Mimicry."

This appears to be another ant mimic spider, possibly in the genus Castianeira. It resembles the image of C. dorsata in

Wolf Spider Family (Lycosidae)

A giant wolf spider (Hogna carolinensis) in San Marcos, San Diego County. The body of females can be up to 35 mm in length. This one is about 30 mm. The U.S. penny is 19 mm in diameter. With the exception of tarantulas and trapdoor spiders, this is one of the largest (and fastest) spiders in San Diego County. It is definitely a surprise when you see one run across your carpet!

See Penny Used In Wayne's Word Size Relationships

Giant Wolf Spider With Egg Sac (Family Lycosidae)

Giant female wolf spider with egg sac attached to her spinnerets. Photographed under a rock at Southwestern Research Station, Cave Creek Canyon, Portal, Arizona. This is presumably the genus Hogna.

Wolf Spider With Spiderlings On Her Back

Female wolf spider with baby spiders (spiderlings) riding on her "back" (abdomen). They hatched from an egg sac attached to her spinnerets. She was conveniently sitting outside the door to my photography room.

A Large Male Wolf or Grass Spider In My Office

Grass Spider Family (Agelenidae)

A grass spider or "corner spider" (Hololema curta) in its web.

Dysderid Spider Family (Dysderidae)

Click on the photograph to see this spider with concrete background removed.

The infamous sow bug killer (Dysdera crocota). Originally native to Europe, it now has a worldwide distribution. This formidable-appearing spider lives under stones or debris on the ground. It does not spin a web for entrapping prey but instead hunts for sow bugs and pill bugs (isopods) in cracks and crevices. It uses its extra large powerful fangs to pierce and feed on these hard-shelled crustaceans. It is a beneficial spider, but can bite if handled carelessly. The venom is not dangerous to humans, but may cause a local allergic reaction that includes stinging and itching. One Internet reference describes the bite as "annoying." Probably its main enemy in coastal San Diego County are colonies of relentless Argentine ants.

The enormous chelicerae (jaws) and fangs of the sow bug killer (Dysdera crocota).
Note the ring of 6 small eyes that are not as well-developed as in jumping spiders.

Sow Bug Eater Holding Its Favorite Prey
A Pillbug: Another Prey Of Sow Bug Eater
More Information About The Argentine Ant

Lynx Spider Family (Oxyopidae)

A green lynx spider (Peucetia viridans) with its prey. It was photographed in bed of shasta daisies (Chrysanthemum maximum) with a Sony T-9 digital camera. The camera was held with one hand and extended at arm's length.

A green lynx spider (Peucetia viridans) with its prey.

A green lynx spider (Peucetia viridans) with its prey.

A striped lynx spider (Oxyopes salticus).

Lynx Spider With Face On Its Abdomen

This unusual lynx spider was in my back yard Christmas eve 2014. It sure looks like the face of a dog or cat on its abdomen, unless it was my strong gin & tonic! It really shows up when the color is reversed. The face has not been altered.

More Images Of The Green Lynx Spider

Huntsman Spider Family (Sparassidae)

A golden huntsman spider (Olios fasciculatus).

Male Golden Huntsman

Male golden huntsman. Note pedipalps with enlarged claw-like tips.

Giant Huntsman

A well-camouflaged giant huntsman spider (Olios giganteus) on the bark of an oak.

A giant huntsman (Olios giganteus) in ominous pose on window frame.

  Giant Huntsman Near Cottonwood, Arizona  

Sac Spider Family (Clubionidae): Miturgidae in some references

A small house spider of the genus Cheiracanthium, a member of the sac spider family (Clubionidae). The body (excluding legs) is about 5 mm long. These spiders are pale or cream-colored with translucent legs. Members of this family spin saclike, tubular resting sites inside a rolled leaf or under bark or a stone. The house-dwelling species builds its saclike silk bivouac in corners, crevices or even inside appliances. Some members of this family can inflict a painful bite. Their long, sharp fangs can readily penetrate human skin. Their venom contains a cytotoxin that destroys tissue, and bite wounds are slow to heal. The most common species found in homes in southern California is C. mildei which is introduced from Europe. They have 8 conspicuous eyes arranged in two rows.

Business end of the sac spider (cf. Cheiracanthium mildei) showing chelicerae (jaws) & fangs.

Crab Spider Family (Thomisidae)

     Crab Spider on Brodiaea       Crab Spider on Hulsea      Crab Spider on Milkweed 

Sandy Desert Spider (Homalonychidae)

Homalonychyus theologus (Sandy desert spider) in Anza-Borrego Desert. According to Lynn & Gene Monroe (2013), this cryptic spider has some ingenius methods of camouflage, including coating itself with sand and joining its legs in pairs (the 2 front pair forward & last 2 pair backward) to resemble dry cactus spines! Outstanding image courtesy of desert naturalist extraordinaire Karyn Sauber.

Bathroom Spider (Steatoda--Family Theridiidae)

My latest house guest: A spider that superficially resembles poisonous brown recluse, only without distinct violin marking. With a 2 yr old who touches everything regularly visiting my home, I must carefully screen all resident spiders! On 27 Jan 2021, I sumitted my 2 photos to iNaturalist and several reviewers thought it was a fase widow (genus Steatoda). Several species occur in my area, including S. grossa. It resembles the male S. grossa image on BugGuide labeled "Bathroom Spider." Some species of Steatoda can bite and are mildly venomous.


  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.

  4. Monroe, L. & G. Monroe. 2013. Desert Insects & Kin Of Southern California. [A Photographic Survey & Natural History Anza-Borrego Desert State Park.] Granite Ridge Nature Institute. Merryleaf Press, Lyons, CO.

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