Hawthorne/Walker Lake areaMineral County, Nevada1–2 September 2007

Participants:Zachary J. Valois, SLCCKelsey A. Neeley, volunteer

We traveled over 1,500 miles to sample the Walker Lake / Hawthorne area Our primary goal was to find one of the remaining species needed for DNA sequencing, Paruroctonus simulatus, at its type locality.. Over 60 scorpion specimens were collected in the Hawthorne area, representing four genera and six species. The Great Basin habitats we encountered were Lahontan Basin Salt Shrub, Tonopah basin, and sagebrush foothills. On the way back to Utah, we spent several more days collecting in other areas in Nevada and southern Utah, collecting an additional 50+ samples. The two-day trip was partially funded by the NSF REVSYS grant.

The majority of the foothills in the area are characterized by

exposed fossilized marine rock, and deposited sand/salt (saltwater flowed from Mono Lake during the Pleistocene).

Over time, wind deposited pluvial sediment from ancient

Lake Lahontan and Walker Lake up onto the foothills

creating a mix of varied microhabitat.

This valley is ancient Lake Lahontan, now partially filled by Walker Lake (surface

elevation 3,960 feet, barely visible the far right) and the Army Depot at Hawthorne.

The lake was extensive during the Pleistocene and went through several dry

periods during the last 10,000 years, even with flow from salty Mono Lake to the south (elevation 6,380 feet) via the

pass at the far left. These dry periods and surface winds account for the dune

systems that now cover much of the area, including evidence of volcanic activity

from the Aurora-Bodie volcanic field, about 4.5–2 million years ago. Small

cinder cones dot the landscape in the distance. In this photo you can see how

erosion exposes the older strata. The high peak at the right is Mount Grant, 11,240

feet.

If you look closely, you can see recent scorpion tracks imprinted in the sand. Interestingly, several other tracks—including this set—reveal that scorpions often pass over—i.e., follow— each other’s tracks, including their own. It seems they do this more often than walking in opposing, or different directions. Individuals often moving in large (3´–8´), seemingly sporadic, circling patterns, crossing over their own tracks. If one individual happens to cross another scorpion’s tracks, they will often follow for several feet, either walking directly along the previous tracks or circling in the direction the tracks were going. I was not able to confirm if this behavior was linked to a specific sex, or even consistent within the same species. The few scorpions we observed that were actively following another's tracks were generally following their own species (Paruroctonus boreus, and in this photo P. becki). Oddly, males were usually found following other males than females, and vice-versa. This behavior likely correlates with pheromone markers. Observations throughout other parts of the year might reveal if this behavior is related to courtship.

The scorpion entering from the top right appears to have followed the track of the scorpion that entered from the bottom right.

A burrow of Paruroctonus becki. Note the fanned mouth of the burrow.

Left photo: P. boreus burrow

Right photo: P. becki burrow

Species diversity and density greatly decreased in the flat areas. This could be due to unfavorable microhabitat and lack of shelter and possibly related to decreased prey availability. Paruroctonus becki was by far the most common species in the flat, bare terrain. The occasional Hadrurus spadix and Vaejovis cf confusus could be found in this type of microhabitat as well.

This small ridge is a “bench”, an ancient shoreline of Lake Lahontan.

The exposed lava rock proved to be the ideal microhabitat for Paruroctonus simulatus and Hadrurus spadix.It turns out that P. simulatus was not nearly as psammophlic as initially thought, with the majority being found in coarse sand, along with areas of high amounts of eroded, exposed rock.

Paruroctonus becki and P. boreus were prevalent in the loose sand.Vaejovis cf confusus was also occasionally seen. Note the aeolian pluvial deposits covering the underlying volcanic rock.

Anuroctonus phaiodactylus and Vaejovis cf confusus were most abundant in the loose, more densely vegetated foothills (high amounts of shrubs and brush, as opposed to the grass-dominated plains) and mountain baselines and bajadas. Paruroctonus boreus was also of considerable density in this microhabitat.

Paruroctonus simulatus

A lone adult male.

3 Adult females, and…

Paruroctonus simulatus feeding on an early-instar Paruroctonus species, probably P. becki.

Paruroctonus becki

Juvenile male inviting an alate ant to dinner. Subadult male.

Second-instar female.

Adult female.

Subadult male Hadrurus spadix

Vaejoviscf confusus

Female

Male

Top left: adult male; top right: juvenile (about fourth instar) male; bottom left: adult female; bottom right: adult female.

Note the pallid coloration of P. boreus from this region.

Paruroctonus boreus

Adult male Anuroctonus phaiodactylus

Transition into Mojave Desert scrub further southeast, where we found some Vaejovis cf confusus. Rock flipping revealed only the one species.

Tikaboo Valley, Lincoln County, Nevada.

Adult male Vaejovis cf confusus

Adult male Vaejovis cf confusus

We give special thanks to Lorenzo Prendini, Jeremy Huff, David Sissom, Warren Savary,Darrin Vernier, Richard Haradon, and foremost Kari McWest.