Characteristics and environmental determinants of natality, growth and maturity in a natural population of the desert scorpion, Paruroctonus mesaensis (Scorpionida: Vaejovidae)



The scorpion, Paruroctonus mesaensis (Vaejovidae) has seven instar stages and moults six times. There is no post-reproductive moult. The average growth ratio between successive instars is 1–38. The average rate of weight increase is 000249/day. This rate fluctuates seasonally: it is highest in spring and lowest in winter and summer. Growth rate is a function of ambient burrow temperature and prey abundance. Body size is determinate. The growth rate of the pectines is significantly greater in males as compared with females. Analysis indicates that the pectines are a secondary sexual trait in males.

Animals mature from 19 to 24 months of age. Matings were observed from May through October. Gestation lasts 10–14 months. First surface appearance of newborn (instar II) is synchronous throughout the population and occurred in early August for five consecutive years. Some females were observed to be gravid for at least three consecutive years. Gravid females carry an average of 48–8 embryos. However, on the average only 19–9 young/female survive to appear on the surface. Factors which may be responsible for this observed decrease include resorption of embryos; death at birth, eclosion or first moult; and maternal and sibling cannibalism. The influence of various environmental factors on reproduction were analyzed. The number of newborn appearing on the surface and the population biomass of newborn showed a high positive correlation with precipitation and vegetation cover.