SCORPION - Pseudouroctonus nr. apacheanus - undescribed species?
Pseudouroctonus nr. apacheanus - undescribed species?
Size: Approximately 30 mm
Group Guild Status
Eutroglophile Predator Uncommon
This scorpion was encountered only rarely during the initial study, and were observed primarily in the entrance area (“…on several occasions.”), with only a couple of occurrences deeper in the cave (Welbourn 1999). Observations during our recent research support the original observation that this species is uncommon in the cave. Over the two years of our study (involving over 200 hours of searching) we observed live members of the species in the cave on only 20 occasions. The maximum rate of population increase for some scorpion species is among the lowest in the entire animal kingdom (Polis 1990). Many scorpion species are long-lived, which is compatible with the biology of species with low recruitment rates. Cave limited species may potentially have even lower recruitment and may live longer due to reduced metabolic rates and low activity levels associated with the relative paucity of available nutrients in many caves.
There is little information in the literature on home ranges of scorpions. Findings for the few species that have been studied, particularly burrowing species, show that they have very limited home ranges. A 16-meter diameter home range is considered large for a scorpion, with ranges for other species limited to a few meters (Benton 1992; Polis 1990). The location of the guano deposit below the bat maternity roost site in the Big Room is 75 meters from the nearest cave surface connection, a distance nearly five times what is considered a large home range for scorpions. The presence of scorpions at this well-defined site (relatively deep in the cave) over a period spanning 20 years suggests that they are probably completing their life cycle in the cave. This is supported by their apparent absence in the epigean environment above the cave, which is dominated by the Arizona striped scorpion (Hoffmannius spinigerus).
Scorpions are normally generalist predators, and may be either active, roaming hunters or sit and wait “ambush” predators (Polis 1990). Based on observations of the Kartchner Caverns scorpion it seems likely that it is an ambush strategist. This would be a more practical strategy in the cave environment where resources are more limited, and where energy expenditure is commonly minimized by many cave macro-invertebrates. The scorpions in the cave may be supported on small, widely-spaced feeding events. Vaejovid scorpions have enlarged pedipalps that they use to capture and crush their prey, with their sting being used more commonly for defense, or subduing particularly large or difficult prey (Polis 1990). The scorpion is the largest resident invertebrate predator in the cave, and may make a meal of any invertebrate of appropriate size for each of its age classes. We have so far not observed the scorpion with prey of any kind. Scorpions commonly prey on species of cave crickets (Ceuthophilus), both on the surface and inside caves (RBP personal observation). Other invertebrates in the cave that are likely prey for the scorpions include the two isopod species and the nicoletiid. The scorpions are probably active in the cave year-round.
The species exhibits incipient troglomorphy (morphological adaptations to the cave environment). We have observed some variability in coloration of the scorpions in the cave, with the tail and pedipalps having varying degrees of pigmentation. The generally pale coloration of the animals is likely a reduction of pigmentation resulting from a long presence of the species in the cave.
Based on our current understanding of the ecology of this animal we believe the Kartchner Caverns scorpion is, at the very least, a disjunct eutroglophilic population of P. apacheanus. It may also be a distinct species. The animals have yet to be found anywhere outside the cave. See the section on current research on this species.
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