We examined egg sac characteristics and oviposition sites of Metepeira calamuchita (Piel, 2001) (Araneidae) at two different habitat types, creosote bush scrub and Prosopis spp. forest patches, at the Ñacuñan Biosphere Reserve located in the Monte Desert of Mendoza, Argentina. At each site, we manually collected egg sacs of M. calamuchita between November and April. We recorded egg sac location, presence of detritus on the egg sac and its colouration. At scrub sites, there was a greater number of egg sacs anchored to the vegetation, while in forest sites most egg sacs were suspended by web threads. In addition, more egg sacs covered with detritus were found at scrub sites, but we did not find an association between egg sac colouration (brown/dark brown) and habitat type. Location of the egg sac and presence of detritus could function as defence strategies in environments with different pressures of egg sac predators and parasitoids.