Tohono Vinegaroon

Mastigoproctus tohono

Tohono Vinegaroon: Arizona's Vinegar-Spraying Whip Scorpion

The Tohono vinegaroon (Mastigoproctus tohono) is a large whip scorpion from southeastern Arizona and northeastern Sonora, Mexico. It has no sting and no venom. It grabs prey with heavy claws and defends itself with a spray that is mostly acetic acid, the acid in vinegar. Until 2018 it was counted as part of the giant vinegaroon, Mastigoproctus giganteus.

Habitat
High desert grassland and mountain foothills
Size
About 56-59 mm long, not counting the whip tail
Diet
Insects, spiders, scorpions, centipedes and other small animals
Range
Southeastern Arizona (USA) and northeastern Sonora (Mexico)
Lifespan
About 7-9 years from egg to death
Conservation
Not evaluated by the IUCN

Habitat & range

The Tohono vinegaroon lives in southern Arizona in the United States and in northeastern Sonora, Mexico (Barrales-Alcalá, Francke and Prendini 2018, Bulletin of the American Museum of Natural History). Most of what is known about it comes from long-term studies by Justin and Li Schmidt in high desert grassland near Willcox, Cochise County, Arizona, at about 1,280 m above sea level (Schmidt and Schmidt 2025, Journal of Arachnology). For most of the year it stays underground. Each animal seals itself into a cell at the bottom of a burrow about 30 to 50 cm deep, where the soil stays between about 3 and 38 °C even when the surface swings from -15 °C in winter to almost 60 °C in summer. It digs out only after the first summer monsoon rains in late June or July, and the Schmidts never saw one on the surface before the first rain in more than 20 years of visits (Schmidt and Schmidt 2025). In their 2.56 ha study plot they estimated up to about 680 vinegaroons per hectare. The species is named after the Tohono O'odham people, whose lands lie within its range (Barrales-Alcalá et al. 2018). It was split from the giant vinegaroon (Mastigoproctus giganteus) in a 2018 revision that turned one North American vinegaroon into seven species, three of them new to science (American Museum of Natural History).

Size & appearance

Vinegaroons are arachnids in their own order, Thelyphonida (also called Uropygi), and are neither scorpions nor spiders (American Museum of Natural History). The type specimens of the Tohono vinegaroon measured 56.5 mm (male) and 59.4 mm (female) from the front of the carapace to the end of the body, not counting the tail (Barrales-Alcalá et al. 2018). The carapace is dark reddish brown to black. The heaviest wild female the Schmidts weighed was 8.35 g (Schmidt, Schmidt and Cowles 2021, Journal of Arachnology). It walks on six legs. The first pair of legs is long and thin and is held forward like antennae to feel for prey, mates and vibrations, because its eight eyes see little more than light and dark (Animal Diversity Web). In front of the head are two thick, spiny pedipalps that work as crushing claws. At the back is a thin whip-like tail, the flagellum, which gives whip scorpions their name. The tail has no stinger.

Diet & hunting

The Tohono vinegaroon hunts only at night. It is an ambush predator that moves slowly, waits for prey to come close, then rushes forward and grabs it with its pedipalps (Schmidt and Schmidt 2022, Journal of Arachnology). In field and laboratory tests near Willcox, adult vinegaroons overpowered most prey of a size they could handle, including chemically defended bombardier beetles and blister beetles, venomous scorpions, male tarantula hawk wasps, giant centipedes, wolf spiders and sun spiders. Only very hard-shelled beetles, giant velvet mites and animals that were simply too big, such as female tarantula hawks, were safe. Prey seen being eaten in the wild included click beetles, June beetles, a sun spider and a scorpion that was eaten tail first (Schmidt and Schmidt 2022). The Schmidts describe vinegaroons as members of the guild of apex arthropod predators in this desert grassland. Adults and the largest young were not preyed on by any predator active in the same places and at the same times.

Behavior & adaptations

Vinegaroons have no venom. When threatened they spray a fine, well-aimed mist from a pair of large glands at the base of the tail. Thomas Eisner and colleagues measured the spray as 84 percent acetic acid, 5 percent caprylic acid and 11 percent water (Eisner et al. 1961, Journal of Insect Physiology). Their specimens came from the Southwestern Research Station in Arizona and belonged to the species now called the Tohono vinegaroon (Barrales-Alcalá et al. 2018). The caprylic acid helps the acid spread over and soak into the waxy outer layer of an attacking insect or spider. Courtship happens at night and lasts nearly 13 hours on average, in four stages called Chase and Grapple, Dancing, Generating and Pressing (Schmidt, Schmidt and Cowles 2021). A female produces 35 to 68 young, about 52 on average, and their combined weight averages 93 percent of her own. The young ride on her back at first and then share her burrow, where she brings them food. Each young vinegaroon molts at most once a year, so reaching adulthood takes about five years under good conditions. About 12 percent of wild vinegaroons in the Schmidts' plot showed injuries, most often a lost tail. They can regrow a tail, sensory legs and even part of a pedipalp at the next molt, but adults no longer molt (Schmidt and Schmidt 2025).

Conservation

The Tohono vinegaroon has not been assessed for the IUCN Red List. In the long-term Willcox study plot the population profile stayed mostly steady over several years, with adults and fourth-stage young making up about 90 percent of the animals seen (Schmidt and Schmidt 2025). The authors did not publish the exact location of the plot, to protect the population from collecting for the pet trade.

Fun facts about Tohono Vinegaroon

  • Its defensive spray is 84 percent acetic acid, the acid that gives vinegar its smell (Eisner et al. 1961).
  • A mother's 52 or so babies can together weigh almost as much as she does, and sometimes more (Schmidt, Schmidt and Cowles 2021).
  • It spends most of the year sealed in an underground cell and comes up only after the summer monsoon rains (Schmidt and Schmidt 2025).
  • Until 2018 the giant vinegaroon was treated as one widespread North American species. A revision showed it is really seven (American Museum of Natural History).
  • Adults have almost no predators in their desert grassland home. In lab tests, even scorpions and giant centipedes ended up as their prey (Schmidt and Schmidt 2022).

Tohono Vinegaroon vs Maricopa Harvester Ant

Tohono Vinegaroon wins one on one against a single worker. Size and armor beat the sting, but a young vinegaroon should stay away.

Both live in southern Arizona, and Justin and Li Schmidt actually tested this pairing in the lab with Pogonomyrmex maricopa (Schmidt and Schmidt 2022). For a small vinegaroon it is a risky meal. Young vinegaroons readily ate the ants, but one ant bit off a vinegaroon's tail, and two young vinegaroons were stung through the soft joints of their pedipalps and died. A full-grown vinegaroon is a different story. It is many times bigger than a single worker, its armored claws keep the ant at a distance, and adult vinegaroons in the same habitat were not preyed on by any arthropod. The Schmidts found that large vinegaroons simply did not bother hunting harvester ants. One ant against one adult is a mismatch. A whole colony would be another fight.

Read more about Maricopa Harvester Ant.

Common questions about Tohono Vinegaroon

Are vinegaroons venomous or dangerous to people?

No. Vinegaroons have no venom and no stinger. Researchers who studied the Tohono vinegaroon for decades call them neither venomous nor dangerous (Schmidt et al. 2021). A large one can pinch with its claws, and its acid spray stings in the eyes or on broken skin (Animal Diversity Web). Compare the real stings in our Schmidt pain index ranking.

Why is it called a vinegaroon?

Because its defensive spray smells like vinegar. Glands at the base of the tail fire a fine mist that is 84% acetic acid, 5% caprylic acid and 11% water (Eisner et al. 196190054-3)). The specimens in that study came from Arizona and belong to the species now called the Tohono vinegaroon (Barrales-Alcalá et al. 2018).

Is the Tohono vinegaroon the same as the giant vinegaroon?

Not anymore. It used to be counted as the giant vinegaroon, Mastigoproctus giganteus. In 2018 a revision split that one North American species into seven, three of them new to science (AMNH). The Arizona and Sonora population became M. tohono, Florida's became M. floridanus, and the name M. giganteus now belongs to a population in Morelos, Mexico (Barrales-Alcalá et al. 2018).

When do vinegaroons come out in Arizona?

After the first summer monsoon rains, usually in late June or July. They spend the rest of the year sealed in burrows about 30 to 50 cm deep. In more than 20 years of visits to one study site, researchers never saw a vinegaroon on the surface before the first rain. Females disappear early, but males stay active until about October (Schmidt and Schmidt 2025).

How long do vinegaroons live?

About 7 to 9 years from egg to death. Young Tohono vinegaroons molt at most once a year and need about five years to grow up, and adults live up to about four more years. Females can raise a litter in each of their second and third summers as adults (Schmidt et al. 2021).

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