Estimation of the Effect of the Predator Scytodes globula (Araneae: Scytodidae) on Loxosceles laeta (Araneae: Sicariidae) Populations

Abstract

It has been reported that Scytodes spiders are predators of spiders of the genus Loxosceles, but the question of the effect of Scytodes globula Nicolet on Loxosceles laeta (Nicolet) populations is still unanswered. The goal of this study is to analyze the population effect of S. globula on the population dynamics of L. laeta by means of simulation with projection matrices, considering the seasonal fluctuation of fecundity, random meetings between the predator and the prey, and limited growth of the L. laeta population. We found that the most important parameters to predict the characteristics of the population at equilibrium are the fertility and the survival function of the spider of advanced developmental stage. Also, the predator S. globula significantly decreases population size, population fluctuations, and the proportion of reproductive individuals of L. laeta. The most probable effect of S. globula on L. laeta populations is a decrease of 20% of the population size. This is insufficient to consider this species as an agent of biological control of L. laeta. However, the action of S. globula is not negligible because decreasing the L. laeta population by about 20% could mean a decrease of about 15% in the incidence of loxoscelism. This action is probably less effective than other epidemiological measures such as house cleaning and insecticides or arachnicides and probably similar to the direct action of humans eliminating one or two spiders per year in their houses, but it helps.