Vegetation as a preferred microhabitat for scorpions has rarely been considered despite many Buthidae (the bark scorpions) being non-burrowing errant scorpions that are active on both the ground and vegetation. Microhabitats can serve multiple functions for Centruroides vittatus (Say 1821), but a particular microhabitat can be preferred for a certain function such as a refuge, foraging, or feeding.Observations of microhabitat use by C. vittatus were performed in Laredo, Texas of the Tamaulipan Biotic Province. Comparisons of microhabitat use by C. vittatus at different temperatures or precipitation levels were performed. Foraging and feeding by C. vittatus among microhabitat classes were also compared. The observed use of vegetation by C. vittatus during different seasons was compared to the expected use based on relative abundance of vegetation in the habitat.Air temperature, but not precipitation, had a significant effect on microhabitat use by C. vittatus. Microhabitat had a significant effect on foraging of C. vittatus with caterpillars comprising 34.6% of the prey items and half of the scorpions feeding on caterpillars were in blackbrush ( Acacia rigidula). The lowest proportion of scorpions observed feeding was on the ground (3.8%) and the highest in blackbrush (40.4%). The frequency of C. vittatus among vegetation classes was significantly different compared to the relative abundance of plant species in the plot. Scorpions were observed on prickly pear cactus (Opuntia engelmannii) and strawberry cactus ( Echinocereus enneacanthus) at a higher frequency than expected, and scorpions were observed on guajillo (Acacia berlandieri) and tasajillo (Opuntia leptocaulis) at a lower frequency than expected. The frequency of scorpions on blackbrush was higher than expected during the spring.Vegetation is an important microhabitat for C. vittatus in south Texas. The results indicate the possibility that C. vittatus in south Texas used various plant species to carry prey captured on the ground into vegetation to feed, used blackbrush to forage for caterpillars, and used strawberry and prickly pear cacti as a possible refuge.

The home range of the desert scorpion Paruroctonus mesaensis is analyzed using techniques of Ford & Krumme (1979). Possible factors influencing home range geomtry of P. mesaensis include prey distribution, prey abundance and renewal, energy requirements, risk of predation and body size. There are differences in home range size among the three year classes with the youngest year class maintaining a significantly smaller home range. Home ranges of each year class are approximately circular indicating that these scorpions are remarkably symmetric in the directional use of space around their burrow. The majority of surface activity occurs within 1.0 m from the burrow for all ages. These patterns along with equal probabilities of prey capture at all distances from the burrow suggest that scorpions do not deplete prey within their home ranges.

Prey capture by the orb=web spider, Argiope aurantia Lucas 1833, depends on the type of the web=site selected. I analyzed A. aurantia web sites in open field and adjacent forest edge habitats to identify habitat features associated with web characteristics and prey capture. In the open field, the use of herbs or grass for web attachment was associated with smaller web diameters, and lower attachment heights and web heights. In both forest edge and open field, the distance to the nearest flower was less when web attachments were on composites. In the open field, webs attached to grass captured more orthopteran prey, and webs attached to herbs and composites captured more hymenopteran prey. The mean number of prey captured and the proportion of hymenopteran prey increased with higher web attachments in the open field habitat. Close proximity of webs to goldenrod in bloom in the open field habitat increased the mean number of prey captured and the proportion of hymenopteran prey. In the forest edge habitat, the presence of goldenrod was associated with more hymenopteran and orthopteran prey and with a higher mean prey number captured. Generally, webs in the open field habitat had more hymenopteran and orthopteran prey and higher mean prey number captured than the forest edge habitat. The web-site providing the greatest probability for encountering and capturing prey is predicted to be one with a tall composite plant for web attachment near goldenrod in bloom.

Variation in venom toxicity and composition exists in many species. In this study, venom potency and venom gland gene expression was evaluated in Centruroides vittatus, size class I-II (immature) and size class IV (adults/penultimate instars) size classes. Venom toxicity was evaluated by probit analysis and returned ED50 values of 50.1 μg/g for class IV compared to 134.2 μg/g for class I-II 24 hours post injection, suggesting size class IV was 2.7 fold more potent. Next generation sequencing (NGS and qPCR were used to characterize venom gland gene expression. NGS data was assembled into 36,795 contigs, and annotated using BLASTx with UNIPROT. EdgeR analysis of the sequences showed statistically significant differential expression in transcripts associated with sodium and potassium channel modulation. Sodium channel modulator expression generally favored size class IV; in contrast, potassium channel modulators were favored in size class I-II expression. Real-time quantitative PCR of 14 venom toxin transcripts detected relative expression ratios that paralleled NGS data and identified potential family members or splice variants for several sodium channel modulators. Our data suggests ontogenetic differences in venom potency and venom related genes expression exist between size classes I-II and IV.

Ontogenetic shifts in activity and habitat use by the scorpion Centruroides vittatus in Laredo, Texas can occur with shifts in microhabitat use, the height of the scorpion in vegetation and seasonal and lunar activity among different sizes of C. vittatus but not taxa of prey in the diet. The microhabitat use by the different size classes was significantly different with significant associations among the cacti with a high frequency of larger scorpions on prickly pear cactus and strawberry cactus and between grass and other vegetation with a high frequency of smaller scorpions on grass. A comparison of the mean height of scorpion on blackbrush among the size classes was not significant but height on grass was significant. The activity of the size classes was significantly different among months and lunar cycle. Temperature had a significant effect on the activity of scorpions by different size classes and in different microhabitats. Caterpillar availability did not have a significant association with either scorpion size class or microhabitat use by scorpions. The taxa of prey captured by the different size classes were not significantly different including no notable difference in scorpions feeding on caterpillars. The size classes of C. vittatus show microhabitat and temporal shifts in activity. The results suggest that smaller scorpions can possibly be avoiding the larger scorpions by reducing activity in the preferred microhabitat (prickly pear and strawberry cactus) of larger scorpions.