spiders

Watching a Western Spotted Orbweaver spider

For the past two weeks, I’ve been watching a spider build an intricate web near my back porch. The circular web is suspended from an ironwork fence by many strands of spider silk.

I have tentatively identified this spider as a Western Spotted Orbweaver (Neoscona Oaxacensis ) also known as a zig-zag spider. It is a pretty spider with a body length of just under one-half inch.

This spider occurs throughout the mid-west and western U.S., Mexico, Central American and parts of South America. Like most spiders, the orbweaver has venom to subdue its prey, but most sources say the venom is not harmful to humans.

The spiders eat insects and anything else that gets caught in its web. It also eats spider silk. You can watch a short video from the Boyce Thompson Arboretum which shows this spider in action:

Spider silk is a protein fiber. Spiders can produce as many as seven different types of silk. Wikipedia has a long and detailed article on spider silk (link). I will summarize.

Spider silk is five times as strong as the same weight of steel and some silk can stretch up to five times its length without breaking.

Types of silk (from Wikipedia):

Major-ampullate (dragline) silk: Used for the web’s outer rim and spokes and also for the lifeline. Can be as strong per unit weight as steel, but much tougher.

Capture-spiral (flagelliform) silk: Used for the capturing lines of the web. Sticky, extremely stretchy and tough. The capture spiral is sticky due to droplets of aggregate (a spider glue) that is placed on the spiral. The elasticity of flagelliform allows for enough time for the aggregate to adhere to the aerial prey flying into the web.

Tubiliform silk: Used for protective egg sacs. Stiffest silk.

Aciniform silk: Used to wrap and secure freshly captured prey. Two to three times as tough as the other silks, including dragline.

Minor-ampullate silk: Used for temporary scaffolding during web construction.

Piriform: Piriform serves as the attachment disk to dragline silk. Piriform is used in attaching spider silks together to construct a stable web.

It seems that spiders are more complicated than one would initially think. Have you seen this spider around your garden?

See also:

The Arizona Brown Spider – a reclusive beastie

Black Widow Spiders
A green lynx spider may be lurking in your yard

Who’s Afraid of Tarantulas?

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Black Widow Spiders

Black widow spiders (Latrodectus hesperus) are normally shy and sedentary, but will react if they feel threatened. According to some authorities, their venom is 15 times more potent than rattlesnake venom. But black widows bites are fatal less than one percent of the time because their small fangs can’t penetrate the skin very deeply and often the spider does not inject venom. Only the bite of the female is potentially dangerous to humans.

Black widowThe female black widow has a body length up to three-quarters of an inch. She is shiny black to dark brown and has a red, hour-glass mark on the bottom of the abdomen. The male is half that size, usually medium brown with cream-colored makings on legs and abdomen.

According to the Arizona-Sonora Desert Museum:

Different species of Latrodectus are found throughout most of North America, more commonly in warmer climates. Black widows are common around man-made structures such as garages, lawn furniture, and woodpiles. They also live in a variety of natural habitats.

The black widow preys mainly upon insects that it traps in the web. The web is irregular and strong to the touch in comparison to other webs. Some species of spider wasps prey upon black widows. Black widows are shy, sedentary, and largely nocturnal. They are not aggressive, but will bite in self-defense.

The female mates only once in her lifetime, retaining sperm for future egg-laying. The smaller male is sometimes eaten by the female following mating, hence the name “widow.” This characteristic, however, is not limited to black widows, but can occur after mating in many arachnids, most of which are highly predatory. The female lays approximately 300 eggs at one time and encases them in a round, cream-colored egg sac made of her silk. One spider produces several sacs within its one- to two-year lifespan, but only one sac at a time. The spiderlings disperse by ballooning.

The black widow is one of two species within our region that is potentially dangerous to humans (the brown spider is the other). The bite can kill a human, but this is rare. More often, the bite is painful and causes serious reactions, including nausea, dizziness and abdominal cramps.

The silk of the black widow and some orb-weaving spiders is the strongest among spiders and stronger than steel wire of the same weight. ASDM notes: “A spider may have up to six types of silk glands, each producing a different kind of silk. It is actually a complex strand of proteins that is produced as a liquid, and solidifies under tension. Silk is used to build webs, catch food, line burrows, protect eggs, detect prey (as trip lines), and even to aid in dispersal.” Spiders avoid being caught in their own webs by having oil on their legs.

Black widows and other spiders prey mostly upon insects that get trapped in their web. The venom serves to paralyze and liquify the prey, so the spider can suck out the insides. Black widows are preyed upon by wasps and lizards.

Most spiders have up to eight eyes, but only the jumping spiders rely on sight to hunt. Most spiders have hairs on their bodies, especially their legs. These hairs allow the spider to feel and “hear” by displacement of air around the hairs.

See also:

A green lynx spider may be lurking in your yard

Cochineal the Little Red Bug

Desert Bees and Africanized Bees

Life on a dead saguaro

New giant tarantula found in Sri Lanka – Video

New scorpion species found in Santa Catalina Mountains near Tucson

Scorpions, Vinegaroons, and Sun Spiders

Tarantula Hawks Deliver The Big Sting

Venomous Centipedes and Cyanide-Oozing Millipedes

Who’s Afraid of Tarantulas?

The most dangerous venomous animals of the Southwest

Speckled-rattlesnakeThe southwestern desert has a reputation for venomous critters, but which are most dangerous? I attended a lecture at the Arizona-Sonora Desert Museum given by James W. Cornett, a biologist, author, and emeritus Curator of Natural Science at the Palm Springs Desert Museum. Cornett has studied venomous animals for over 30 years and gave us a list of what he considers the thirteen most dangerous animals.

This list is subjective and includes consideration of the toxicity of the venom, the amount of venom injected, the possibility of an allergic reaction, the abundance of the animal, and the probability you could actually encounter the animal. Here is his list from the least dangerous to most dangerous:

13. Tarantulas. The venom is generally not dangerous to humans and it takes much provocation to get a tarantula to bite you.

12. Centipedes. Some of these can get over 20 inches long (but most are about 5 inches) They deliver venom by pinching with its front legs. One death has been attributed to a centipede bite.

11. Velvet ants (actually wasps). These look fuzzy and cute but deliver a very painful bite.

10. Gila monster. These lizards are venomous but it takes much provocation to get them to bite you.

9. Coral snakes. The coral snakes in the Southwest are generally small. More deaths occur in the East where the snakes are larger.

8. Cone-nosed bugs (aka Kissing bugs). Bites from these bugs can produce an allergic reaction and can transmit Chagas Disease, a chronic and debilitating protozoan infection. Cone-nosed bugs feed on the blood of other animals, mostly rodents.

7. Ants. Swarming ants, by their large numbers can deliver painful bites and cause allergic reactions.

6. Scorpions. Most scorpion stings in the southwest are not dangerous. However, bark scorpion venom is dangerous to humans.

5. Brown (recluse) spiders. The venom is very persistent and causes tissue damage.

4. Wasps.

3. Black Widow spiders. Drop for drop, black widow venom is the most toxic of any animal in the southwest. And now, we are seeing more Brown Widow spiders coming into the area.

2. Rattlesnakes. This venom does great tissue damage and two species, the Tiger rattlesnake and Mohave rattlesnake also have neurotoxic venom. By the way, there are 18 rattlesnake species common to Arizona.

And the most dangerous venomous animal:

1. Africanized Honey Bees. According to Cornett, bees cause more deaths than all the other animals combined.

Besides these animals, Cornett mentioned some snakes that are considered only mildly venomous, some of which are commonly kept as pets. None of these snakes have fangs, but the do have enlarged back teeth and toxic saliva. They need to chew on you for a while to work the venom in. These snakes include the ring-necked snake, black-headed snake, spotted night snake, lyre snake, hog-nosed snake, and the common garter snake.

Cornett related an incident with a hog-nosed snake. This snake was in an exhibit at the Palm Springs Desert Museum. Cornett was attempting to feed it a mouse, but since he handled the mouse, its scent got on Cornett’s hand. The snake bit him on the web between thumb and forefinger and chewed for a while before it could be detached. This mild venom caused swelling and discoloration of Cornett’s hand and arm and produced blisters for about a month. Nobody has antivenom for these snakes.

For more information on venomous animals, see:

Desert Bees and Africanized Bees

Scorpions, Vinegaroons, and Sun Spiders

Tarantula Hawks Deliver The Big Sting

Venomous Centipedes and Cyanide-Oozing Millipedes

Who’s Afraid of Tarantulas?

Rattlesnakes

Venomous Lizards