arachnids

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?

New scorpion species found in Santa Catalina Mountains near Tucson

AZCentral.com reports that a new species of scorpion, dubbed Vaejovis brysoni, has been found in the Santa Catalina Mountains. Rich Ayrey, a Flagstaff nurse and former biologist recognized it as a new species. Ayrey has discovered and named five other scorpion species. This particular scorpion was found by University of Washington post-doctoral scholar Robert Bryson, who spotted it in the Santa Catalina Mountains and sent samples to Ayrey and a collaborator to identify last April. The 2-inch-long, mahogany-colored scorpions were found above 6,000 in the mountains during a hiking trip. This discovery is the 10th known mountain scorpion species in Arizona.

See the full story here.

A-new-scorpion

Scorpions, Vinegaroons, and Sun Spiders

Arachnophobes, this one’s for you. Scorpions, vinegaroons, and sun spiders are arachnids which means they have eight legs, simple eyes, pincers, and two main body parts: the abdomen and the cephalothorax (a fusion of head and thorax). Vinegaroons and sun spiders also have powerful jaws. You may see all three in or around your house if you live in southern Arizona.

SCORPIONS

Stripe-tailed scorpionScorpions have been around for about 400 million years. There are over 1,700 described species of which 30 species live in Arizona. The stripe-tailed scorpion is the most common in Arizona, followed by the bark scorpion, and the giant hairy scorpion. Both bark and stripe-tailed are two to three inches long. The giant hairy scorpion is up to six inches long.

Scorpions are nocturnal and diurnal. They feed upon insects, spiders, centipedes, and other scorpions. The larger scorpions go after small lizards, snakes, and rodents. In turn, they are preyed upon by owls, lizards, snakes, rodents, and bats.

Scorpion mating is a dangerous game because either one may eat the other. Mating does not involve primary copulation. Rather the male deposits a sperm packet on the ground and engages in an elaborate “dance” with the female to maneuver her over the packet. She then takes it up and may store it internally for months. She gives live birth and the newly hatched young ride on mom’s back until their first molt.

Giant Hairy ScorpionIn Arizona, only the bark scorpion has venom potentially life-threatening to humans. About 25 other species throughout the world have dangerous venom. The sting comes from the tip of the tail (the telson). The sting of a bark scorpion is about as painful as that of a bee or wasp. Symptoms of envenomation include numbness, frothing at the mouth, difficulties in breathing (including respiratory paralysis), muscle twitching, and convulsions. Deaths are rare (unless you are allergic to the venom). There is an antivenom available.

Bark ScorpionThe bark scorpion is the only one in Arizona that prefers to climb and it can cling to the underside of objects (like a piece of bark, a rock, a shoe, a piece of clothing, or a ceiling). In the house, they may get trapped in a sink or bathtub, or hide in dark areas of a closet. Outside, they may be in any loose pile of debris. The bark scorpion is the only one tolerant of others of its kind, so may live in large groups, especially in winter.

Scorpions contain a substance in their exoskeleton that makes it impermeable. It also causes scorpions to fluoresce under ultraviolet light. If you take a black light out on a summer night, you might be amazed at how many scorpions are around.

VINEGAROONS

VinegaroonVinegaroons are also known as whip scorpions. There are both tailed and tailless varieties. Although they may look formidable, they lack venom and are harmless. They do, however, have the ability to spray you, from an opening near the tail, with acetic acid (vinegar), and a solvent that attacks the exoskeleton of insects. You can handle them (see here). They are usually three to four inches long and black to dark brown.

They have four pairs of legs, but the front pair of legs are modified to act as feelers. These front legs resemble whips and are covered with many fine hairs. Vinegaroons feed mainly upon insects.

Tailless whipscorpionThese animals occur throughout southeastern Arizona and Sonora, usually at higher elevations. They may be found under rocks, tree bark, or in debris. Like scorpions, the young ride on mom’s back (see here).

 

 

 

 

SUN SPIDERS

SunspiderSun spiders are not spiders but Solpugids (or solifugae). They are also known as wind scorpions. They lack venom and are harmless. However, they have formidable jaws. They are usually one to three inches long, yellow to tan, and very hairy. They are also very fast, voracious predators. Like the vinegaroons, the front pair of legs are used as feelers.

Sun spiders prey upon insects, other arachnids, and small vertebrates, including lizards. Sun spiders are nocturnal, and good diggers. They spend most of their time underground. They are most active in Arizona during the spring and summer. I occasionally find one in my house. I generally leave them alone because they will hunt down insects, spiders, and scorpions.

Mating involves a “dance” and stroking. The male will turn the female over and deposit sperm, which the female can store for later fertilization. She will dig a burrow and deposit up to 100 eggs, but does not care for them.

Old world varieties of sun spiders, some known as camel spiders,(the subject of some wild urban legends) can get very big, about six inches long.

See also: Why do scorpions glow under UV light?