IHeartMantids

November SOTM: Uroctonus mordax

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Uroctonus mordax

 

U. mordax is a small, robust species of forest scorpion found in the western US, with adults topping out at around two inches in length. It is known by a variety of common names, including California forest scorpion, Western wood scorpion, and Mordant scorpion. In a recent revision of systematics, Soleglad and Fet placed it in family Chactidae, while some scientists maintain that it belongs in family Vaejovidae. It is the most common species in its genus which currently contains two other species (U. franckei and U. grahami), both of which have only small ranges within California.

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Adult female from Oregon Coast Range

Coloration of this species is typically dark brown on the entirety of the body with the exception of the legs, which are generally a lighter yellow color. Some variations of color can be seen between different populations (i.e., some populations may be a lighter shade of brown).

 

This species is not considered aggressive or dangerous. Its primary defense is to tuck its legs and metasoma in, using the pedipalps to shield the face, and play dead. If this fails it will likely try scurrying to safety. Stings are not common and the venom is reported to only have mild effects.

 

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Juvenile “playing dead”

Range

 

U. mordax is native to western North America. It can be found in a large area of California, western Oregon, and southern Washington. In Oregon, it is the most common species of scorpion, a fact that surprises many native Oregonians when they first learn of it.

 

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Range of U. mordax in western US

 

Habitat

 

Being a forest scorpion, U. mordax is more often found in forested areas with a relatively high humidity. Collectors have observed that the best places to find this species seem to be rocky slopes that are exposed to sunlight during the majority of the day. During periods of hot, dry weather, collecting is less successful than after rains. It is likely that this species shelters deeper in burrows during such times.

 

During personal collecting trips, the author noted finding specimens underneath plywood and rocks that had been in sunny areas during the day, as well as finding at least two specimens wandering about at night outside of shelter. Suggestions that this species inhabits rotting logs have not been verified. All specimens collected by the author were collected at above 800 feet elevation.

 

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This hillside yielded three specimens, all found near its base

 

Captive care

 

Captive care for U. mordax is very easy. They require several inches of damp substrate that will allow for burrowing, such as coconut fiber or peat. Hiding places should also be provided. Some individuals will utilize these and occupy a shallow scrape underneath a rock or piece of bark, but others will burrow into the substrate. Even specimens that burrow will likely wander about at night, providing a good opportunity for observation.

 

Humidity should be provided by keeping the substrate moist (as with any forest scorpion). A water dish is optional. This species can tolerate periods of dryness but will likely burrow deeper into the substrate in an effort to find moisture. Supplemental heat is not necessary as this species occurs in cooler temperate climates. Some hobbyists suggest a wintering period either by keeping specimens in a home refrigerator for around a month or by keeping them in a cooler portion of a house, such as a garage or basement.

 

This species is reported by hobbyists to be communal but cannibalism is not unheard of. Several instances of second-instar cannibalism have been observed by the author, as well as one instance of an adult female eating a slightly smaller tankmate that was occupying the same burrow. (The female in question was removed to see if this may have been due to her being gravid and thus more temperamental.) This particular case was in a community of one male and five females in a ten-gallon terrarium.

 

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Example of Uroctonus mordax community tank

 

Feeding

 

As with many species, prey should be offered on a weekly basis. This species will readily accept prey when hungry, but may sometimes fast or run away from prey if startled. Uneaten leftovers or rejected prey should be removed within a day of feeding. Prey items can be up to around the same size as the scorpion in question, although young specimens have been observed to readily accept prey larger than themselves. U. mordax will often sting its prey.

 

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Second-instar U. mordax attempting to capture a large prey item

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The next day

 

Sexing

 

When observing adult specimens, it is fairly easy to distinguish between males and females. Females have a very glossy sheen to the tergites while males’ appear matte.

 

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Female on left, male on right

Sexing is also fairly easy by examining the pectines, especially on adults. The tooth counts are eight to 12 for females and 11 to 15 for males – there is some overlap, but in adults the males’ pectines are MUCH larger than the females’.

 

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Adult female pectines

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Adult male pectines

Note the differences in overall size as well as tooth length.

 

 

Breeding

 

Captive breeding has yet to be observed by the author, but varying sources suggest breeding occurs in either early spring, or late fall after the females’ previous broods have dispersed. It is possible that both are true and are range-dependent. For example, females in a warmer climate may mate in the spring and have their young develop faster under warmer temperatures, whereas females from cooler regions may require several more months for their young to develop and would thus mate in the fall and overwinter while gravid.

 

 

Rearing

 

The author has had one female give birth in his care, to a brood of 26. The young began molting at around ten days and stayed on the mother for around 14 days. All juveniles survived to second instar. Five were given away (at least four died later on; most of the deaths were attributed to poor husbandry) and 21 were kept in a juvenile community to see how tolerant they were of each other. Five died for unknown reasons and only 10 were recovered after around two months in the community, suggesting that six were cannibalized. The second-instar young were then separated to prevent further cannibalism and to better ensure that all individuals had access to prey. They began molting to third instar at an age of about three months, and eight of the ten had done so by four months.

 

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Female with brood

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Recently dispersed 2I young

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Second-instar U. mordax

Resources suggest that U. mordax takes around two years to reach maturity, during which time they molt six times to complete development at seventh instar. In the wild females give birth from August to October (the female detailed above gave birth in July, possibly sped up by warmer temperatures in captivity). Total lifespan is reported at four to six years.

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Keep up the good work Mike looks awsome :D really put alot of work into it :D

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Great article, mike!

Any idea what counties in WA they are found in?

Maybe a road trip is in order ;)

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Thanks all! I loved having a chance to put down all the useful information I knew about my favorite species. (The map is also my favorite part -- I've done that for most of the species I currently have.)

 

 

I'm only missing the sources used, might be handy to do some further reading ;)

 

Trying to think . . . the majority is from personal experience and observation, a bit was from the previous SOTM for this species, the map is my own work based on a range map shown at www.toxinology.com, a few things are from Kari McWest's work . . . the rest are just odds and ends I picked up all across the net.

 

 

Any idea what counties in WA they are found in?

Maybe a road trip is in order ;)

 

I know of one person who observed them in Klickitat County near White Salmon (I've heard that county referenced a few times), and I've heard something about them living in the Mt. St. Helens region. There's a photo of one on BugGuide.net found in Skamania County.

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Thanks all! I loved having a chance to put down all the useful information I knew about my favorite species. (The map is also my favorite part -- I've done that for most of the species I currently have.)

 

 

I'm only missing the sources used, might be handy to do some further reading ;)

 

Trying to think . . . the majority is from personal experience and observation, a bit was from the previous SOTM for this species, the map is my own work based on a range map shown at www.toxinology.com, a few things are from Kari McWest's work . . . the rest are just odds and ends I picked up all across the net.

 

 

Any idea what counties in WA they are found in?

Maybe a road trip is in order ;)

 

I know of one person who observed them in Klickitat County near White Salmon (I've heard that county referenced a few times), and I've heard something about them living in the Mt. St. Helens region. There's a photo of one on BugGuide.net found in Skamania County.

 

IHeart,

 

That's about the extent of the published range of U. m. mordax in Washington State.

 

Luc

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IHeart,

 

Very informative and insightful treatment of U. m. mordax. Great work!

Courtship and mating behaviors in this species are stereotypical for scorpions in general (Initiation, PaD, Sperm transfer, Separation, with stereotyped secondary behaviors), with the males utilizing a sexual sting during the initial or mid-stages of the promenade a deux.

 

Cheers,

Luc

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Luc, thanks for the info on this species' courtship. I'd love to see it myself sometime (maybe I should take my only male out of the communal tank for the time being).

 

I attempted mating him with one of my females a month or two after she'd had her brood but there didn't seem to be any interest. I'll give them a cooling period soon (the cold living room instead of the warm invert room) and then try again in the spring.

Edited by IHeartMantids

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