Hot and not-so-hot females!

For ectothermic organisms, environmental temperatures can influence a number of biological processes such as metabolic rate, immune function and locomotor performance. Thus, the body temperatures selected by pregnant females can also affect the health and viability of offspring.  In this study, Drs. Javier A. Rodriguez-Robles, Allen G. Gibbs and I tested the thermal preferences of pregnant and non-pregnant female Arizona Bark Scorpions. We also compared rates of water loss between pregnant and non-pregnant female scorpions. By conducting this study, we hoped to find out more about possible tradeoffs experienced by pregnant females in which the selection of higher preferred body temperatures may lead to higher rates of water loss, which may ultimately compromise their survival in arid environments. The interesting results of our study can be found here! PDF

Webber, M.M., Gibbs, A.G. and J.A. Rodríguez-Robles. 2015. Hot and not-so-hot females: reproductive state and thermal preferences of female Arizona Bark Scorpions (Centruroides sculpturatus). Journal of Evolutionary Biology, 28(2): 368-375.


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Creatures of the Night with Dr. Michael M. Webber!

Have you ever wondered what animals are lurking in the desert at night? Find out in this episode of “Creatures of the Night”. In this episode, you can follow me as I tagged along with other biologists who get to work with nocturnal desert animals such as frogs and toads, bats, snakes and (of course) scorpions. Check it out!

CotN Image

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Scorpion vs. Centipede!

During a nocturnal survey in the Sonoran Desert, Dr. Matthew Graham (Eastern Connecticut State University) and I observed a female Arizona Bark Scorpion (Centruroides sculpturatus) consuming a Sonoran Desert Centipede (Scolopendra polymorpha). We found the scorpion clinging to the vertical surface of a rock, upside down (characteristic of bark scorpions) with the centipede dangling from its mouthparts (chelicerae) and pincers (chelae).


Female Arizona Bark Scorpion feeding on a Sonoran Desert Centipede

Interestingly, the centipede was about twice the length of the scorpion! Centruroides sculpturatus are relatively small-bodied scorpions that possess slender chelae, so we find it astonishing that these scorpions would be capable of catching and subduing a prey item of this size. However, bark scorpions possess extremely potent venom, which may allow these scorpions to quickly subdue these large and potentially dangerous prey items. In desert ecosystems where encounters with prey may be rare, the water and nutrients available from large thick-bodied arthropods like centipedes could be worth the risk.
Check out our natural history note published in Western North American Naturalist! PDF

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It’s hard to hunt with babies on your back!

In nature, animals are often faced with limited resources (i.e. time and energy). When faced with this problem, there are often compromises in the amount of time and energy an animal can devote to a particular activity at any given time. Activities associated with reproduction (e.g. mate searching, copulation, pregnancy, offspring care) can be time consuming and energetically expensive. This is especially true for viviparous (live-bearing) females. During pregnancy, females often experience significant increases in body mass. In addition, the continuous allocation of nutrients to offspring throughout pregnancy is also energetically taxing for females. These reproductive costs are known to negatively impact a female’s ability to move efficiently. I was interested in whether these reproductive costs also increase the difficulty of capturing and subduing prey. Using Arizona Bark Scorpions (Centruroides sculpturatus), Dr. Javier A Rodríguez-Robles and I tested whether reproduction had a negative impact on the predatory efficiency of females. As part of our experiment, we recorded how long it took female bark scorpions to successfully capture and subdue a prey item (Common House Cricket). We compared the prey handling times of female scorpions at different reproductive stages 1) Non-pregnant, 2) Pregnant, and 3) females exhibiting maternal care (i.e. carrying offspring on their backs).

Female Arizona Bark Scorpion stinging a cricket.

Female Arizona Bark Scorpion stinging a cricket.

What we found was that pregnancy did not significantly reduce the predatory efficiency of female Arizona Bark Scorpions. In fact, pregnant females were just as good at catching prey as non-pregnant females. However, females experienced a decrease in their predatory abilities during the maternal care period and they were unable to capture prey. We also wanted to see how long it took females to recover their predatory abilities after the maternal care period, so we removed the offspring from their backs and retested their prey handling abilities 24 hours and 28 days later. What we found was that 24 hours after offspring removal, females were unable to capture prey. However after 28 days, females were significantly better at catching prey compared to females carrying offspring and females 24 hours after offspring removal, but were still slower than non-pregnant and pregnant females. Our results demonstrate that female Arizona Bark Scorpions experience a tradeoff between caring for offspring and capturing prey. In addition, we also observed that reproduction can change the way in which female scorpions hunt for prey.

You can read all of the exciting details of our study in BMC Evolutionary Biology! (

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More new scorpion species!

The discovery that scorpions fluoresce under ultra-violet light marked a revolution in our knowledge of scorpion diversity. Before then, only large, abundant, or commonly encountered scorpions were well-known. However, following this discovery, scorpions began to accumulate in biodiversity collections, and many new scorpion species were described worldwide. In fact, many new scorpion species are still being discovered in places as seemingly well-studied as the United States!

Although at first glance, scorpions may appear to look the same, upon closer inspection one will notice differences in color, shape, size and body proportions among different species. In addition to examining the evolutionary relationships between different species using scorpion DNA, scorpiologists (yes, that is a real job) use these differences to identify and describe different species. Recently, Dr. Robert W. Bryson Jr. (University of Washington) discovered a new scorpion species in the Santa Catalina Mountains, less than 10 miles from metropolitan Tucson, Arizona, USA.

Mr. Richard F. Ayrey and I were lucky enough to get the chance to describe this new species. We named the new scorpion Vaejovis brysoni in honor of our colleague who found and collected the specimens we used to describe the new species. Our findings were recently published in the open access journal ZooKeys (PDF). We were also fortunate enough to be given a chance to talk about this discovery on Arizona Science Illustrated ( a science program which airs on PBS stations in Arizona; see full interview here Researchers Find New Scorpion Species in Catalinas).


New scorpion species (Vaejovis brysoni) that was discovered in the Santa Catalina Mountains near Tucson, Arizona, USA.

Meanwhile, on the other side of the world, a new and rare species of scorpion (Euscorpius croaticus) was described from the Velebit Mountains in Croatia. Dr. Matthew R. Graham, Gergin Blagoev, Natalia Ivanova, Dr. Victor Fet and I described this new species. Our species description was recently published in Revista Ibérica de Arachnología (PDF).


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A Novel Thermal Gradient Design!

For ectotherms (also referred to as cold-blooded organisms), environmental temperatures can influence a variety of life history traits (ex. adult body size, metabolic rate, locomotor ability, movement patterns, foraging and feeding rates, reproductive output and offspring viability). As such, ectotherms are very sensitive to changes in environmental temperatures, and they use a behavior called thermoregulation to control their body temperatures. Thermoregulation can consist of moving to habitats with suitable temperatures, increasing or decreasing the duration of basking behaviors, or through alterating the way that their bodies are in contact with the substrate. Understanding the ways that organisms interact with their environment can help uncover factors that have influenced their ecology. One way to investigate the thermoregulatory behaviors of organisms is to use a thermal gradient. These gradients usually consist of an enclosure offering two extremes in temperature (one cold end and one hot end). In between these two extremes exist range of temperatures that an organisms can choose. This temperature is referred to as a “preferred body temperature”. In my latest publication in the journal Euscorpius, Dr. Robert W. Bryson Jr. and I describe a new method of constructing a (cost-effective) thermal gradient to study the thermoregulatory behaviors of small-bodied ectotherms.

Webber, M.M. and R.W. Bryson Jr. 2012. A Novel Thermal Gradient Design for Small-Bodied Ectotherms. Euscorpius, No.140 (19 May 2012). [PDF]

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New scorpion species discovered in Death Valley!

Wernerius inyoensis. Photo by Matthew R. Graham

Even in places as well-studied as the national parks of North America, new species are still being discovered. With the help of ultra-violet light (which causes scorpions to glow bright-green, Matthew Graham (a fellow UNLV PhD candidate) found the specimen during a scorpion inventory of the Death Valley National Park in 2009.

Recently, Matthew Graham, Dr. Jef Jaeger and I have described the elusive new scorpion species, Wernerius inyoensis (named after the Inyo Mountains where it was found). We published our findings in the open access journal ZooKeys. [PDF]

Webber MM, Graham MR, Jaeger JR (2012) Wernerius inyoensis, an elusive new scorpion from the Inyo Mountains of California (Scorpiones, Vaejovidae). ZooKeys 177: 1-13. doi:10.3897/zookeys.177.2562

Northern Scorpion glowing under UV light

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Reproduction and feeding in Sidewinder Rattlesnakes.

In nature, organisms spend various amounts of time and energy engaged in different activities (ex. feeding, sleeping, mating). During certain times of the year, both time and energy may be a limited resource, and when they are invested into one activity they cannot be simultaneously invested in another. In these cases, organisms must compromise and divide their time and energy among competing activities. These compromises are referred to as life history tradeoffs.

For many organisms, reproduction can take up large portions of an animal’s energy reserves and can be very time consuming. This is especially true for females. During pregnancy, females must carry around the weight of developing offspring in addition to providing nutrients. These costs of reproduction may interfere with other activities that females might engage in like foraging and feeding. Previous studies have shown that reproductive females can exhibit seasonal anorexia, where females will cease feeding during the reproductive season. Seasonal anorexia is hypothesized to alleviate conflicts between reproduction and feeding by allowing a female more time and energy to engage in reproductive activities. Drs. Javier A. Rodríguez-Robles, Xavier Glaudas and I decided to investigate possible tradeoffs between reproduction and feeding in the Sidewinder Rattlesnake (Crotalus cerastes).

Sidewinder Rattlesnake (Crotalus cerastes)

To help answer our questions regarding the feeding behavior of Sidewinders during the reproductive season, we dissected museum specimens and checked their stomach for prey items (lizards, rodents, birds). We checked to see if the frequency in which we found prey, differed during certain times of the year.

The results of our study were published in the journal Copeia [PDF]

Webber, M.M, X. Glaudas and J.A. Rodríguez-Robles. 2012. Do Sidewinder Rattlesnakes (Crotalus cerastes) Cease Feeding during the Breeding Season? Copeia 2012 (1): 100-105.

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