Wryheat Top Ten Stories

These ten stories were the most viewed for this blog:

Tarantula Hawks Deliver The Big Sting

Edible Desert Plants – Barrel Cactus Fruit

NASA Says Earth Is Entering A Cooling Period

Creatures of the Night: Kangaroo Rat

Gulf Oil Disaster – Beneath the Waves

Cancun Climate Conference, Japan Says No To Kyoto

What happened to the Gulf oil

Geologic Setting of Icelandic Volcanoes

The Chevy Volt, just the latest expensive toy

NASA’s Mono Lake Arsenic Microbes Not Quite As Advertized

To see a complete list of stories with links visit the Quick Link Index page.

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.


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.


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).






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?

Tarantula Hawks Deliver The Big Sting

Tarantula Hawks, a.k.a., Pepsis Wasps, have the most painful sting of any insect, and they live here in the southwestern desert. There are 15 species in North America, some up to four inches long. The most common species in Arizona appears to be Pepsis formosa, a bluish-black wasp with orange wings. These can get up to two inches long.


Just how painful is the sting? Well, on the Schmidt Sting Pain Index, Pepsis wasps (and Bullet Ants) register a 4. Africanized bees, yellow jackets, hornets, and bumble bees register a 2. Dr. Justin Schmidt, an entomologist, recently retired from the U.S. Department of Agriculture’s Tucson Carl Hayden Bee Research Center, allowed himself to be stung by a variety of insects so he could judge the amount of pain. How’s that for a job? Schmidt poetically describes the Pepsis wasp sting as “Blinding, fierce, shockingly electric. A running hair drier has been dropped into your bubble bath.” (He describes the sting of a Bullet ant as pure, intense, brilliant pain. Like fire-walking over flaming charcoal with a 3-inch rusty nail in your heel.) The pain from a Pepsis wasp sting is said to last only three (very long) minutes.

Although their sting is traumatic, Pepsis wasps are not aggressive and it takes provocation to get one to sting you. So, don’t try to catch one in your bare hands. Only the females sting (but males may fake it), because the stinger is derived from the ovipositor, the egg-laying organ. You can distinguish females from males by the curled antennae of the female.

See the Bug guide for more photos.

Pepsis wasps are most active in the summer although they do try to avoid the hottest part of the day. They are found around flowers or on the ground in search of prey. The adult Pepsis wasps feed on nectar and pollen. It is called a tarantula hawk because it hunts tarantulas (and other large spiders) to use in the wasp’s reproductive cycle. The Pepsis wasp will approach a tarantula and cause the spider to rear its legs, thus exposing its abdomen. The wasp will sting the spider to paralyze it. The wasp will lay an egg on the paralyzed spider and drag it to a hole, bury it, and cover up the hole. When the wasp egg hatches, the larvae eats the flesh of the living tarantula for about 35 days, then spins a cocoon and pupates over the winter. If the wasp egg fails to hatch, the spider can recover.

Most predators avoid the Pepsis wasp. However, roadrunners and bullfrogs are known to tackle them.

Recently my wife, Lonni, saw a very large all-black wasp on our back porch. She claimed it was more than four inches long. For some reason she didn’t get a photo. It might have been a large example of Pepsis mexicana (photo below from http://www.arizonensis.org/sonoran/ ).


By the way, Pepsis formosa is the New Mexico State Insect. (Arizona’s state insect is the two-tailed Swallowtail, a butterfly.)

Videos of Pepsis wasp attacking a tarantula:

Part 1, the attack: http://www.youtube.com/watch?v=5C1wFxEIj8E

Part 2, the kill: http://www.youtube.com/watch?v=D56lxph_WlI


Who’s Afraid of Tarantulas?

The Desert Tarantula, Aphonpelma chalcodes, is the most common tarantula seen in the Tucson area and is one of 30 species found in Arizona. Now, during the monsoon, and into early fall is the time to see them. If you notice holes in your yard about the size of a quarter, it is probably a tarantula hole. You can go out at night with a flashlight and observe the females near their holes. Males are more likely to be seen trekking to find females.

Tarantulas are primitive spiders that evolved almost 350 million years ago and have changed little since. The female Desert Tarantula is usually tan or brownish, while the male is darker, usually with black or dark legs and a reddish abdomen. Females have a large abdomen, bigger than the cephalothorax(upper body), while the males have a small abdomen.

Tarantula female

Tarantula male

Tarantulas dig burrows about 6 inches deep and up to 8 inches laterally, enlarging them as the spider grows. The spiders molt 3- to 6 times a year as they grow, and they can regenerate lost legs upon molting.

Tarantulas are venomous like all spiders, but they are very docile and bite only under extreme provocation. I have picked up many tarantulas and never have been bitten. The venom is usually not harmful to humans. But tarantulas have another defense. Some of the hairs on their abdomen are barbed (urticating hairs) and are very irritating. The tarantula uses its hind legs to flick these hairs at an attacker.

Tarantulas are long lived spiders. They reach sexual maturity at 8- to 12-years old. Females can live up to 25 years, but the males live only one season beyond sexual maturity. Mating takes place in the summer and fall, and the female stores the sperm until the next spring. The female spins a thick layer of silk in her burrow and in concealed places near the burrow to hold up to 300 eggs. Ants are the main predators of the eggs. The spiderlings hatch in about three weeks and stay in the silk cocoon for another 7 weeks while they grow. The survivors disperse and make their own burrows.

When active, tarantulas may set out strands of silk, “trip wires” around their burrow as a signal that a meal is passing by. They don’t like water, and flee if the burrow gets wet. Sometimes a silk cap on the burrow helps keep water out. Tarantulas do need to drink, but can go up to 90 days without water. During the winter, tarantulas become dormant. They plug their holes with silk and soil, and wait for summer.

Pepsis waspAnd now for a gruesome tale. The Pepsis wasp, Pepsis formosa, is a large (up to 2 inches), bluish-black wasp with orange wings. It is also know as the tarantula hawk. It is a parasite on tarantulas and uses the spiders in its reproductive cycle.

The Pepsis wasp will approach a tarantula and cause the spider to rear its legs, thus exposing its abdomen. The wasp will sting the spider to paralyze it. The wasp will lay an egg on the paralyzed spider and drag it to a hole, bury it, and cover up the hole. When the wasp egg hatches, the larvae eats the flesh of the living tarantula for about 35 days, then spins a cocoon and pupates over the winter. If the wasp egg fails to hatch, the spider can recover. These large wasps generally don’t bother humans.

Tarantulas may look scary, but they are very gentle creatures. You need not be aftraid.