Metepeira  atascadero

          Metepeira atascadero Piel occurs in desert-mesquite grassland habitat near San Miguel de Allende, Guanajuato.  Conditions are typically severe and fluctuating in this habitat, with low seasonal rainfall (< 60 cm/ yr), low relative humidity (45 to 65%), and wide daily temperature range (approx. 8 - 33 ^oC).  M. atascadero live solitarily or in small groups of two to ten individuals in patches of cactus or mesquite, maintaining considerable distance between individuals. 

Variation in climatic conditions and their subsequent effect on prey have a dramatic influence on colonial behavior in this species.  In years when prey availability is low, approximately 65-80% of the spiders forage solitarily; the remaining 20-35% forage in small groups of two to five individuals. In years of high prey abundance (during or following El Niño events) approximately 30 - 40% of the spiders forage solitarily; the remaining 60-70% forage primarily in groups of two to ten individuals (Hieber and Uetz 1992).

M. atascadero web

M. atascadero habitat

M. atascadero are active foraging on webs from June to November, and because of the seasonal availability of prey, they produce only one generation a year.  Spiderlings overwinter in their egg-sacs (December to May) and emerge into an environment bereft of existing colonies, with patches of vegetation suitable for web location scattered throughout the habitat.  Web sites are critical for survival, and web defense is highly aggressive, often escalating to dangerous levels (Uetz and Hodge 1990; Hodge and Uetz 1995).