Spiders

Spiders are abundant terrestrial arthropods. Actually more than 40,000 species are known (World Spider Catalog, 2015). They produce venom for defense and prey capture and only a few species are dangerous for humans. They succeed in almost every terrestrial environment and are regulators of insect populations for their abundance (Haddad et al. 2004, Chatterjee et al. 2009). Spiders are very important in ecological studies as environment quality indicators and as biologic control agents in agroecosystems, therefore they are ideal organisms for biological monitoring (Pearce & Venier 2006, Cristofoli et al. 2010). Almost all arachnids are good ecosystem degradation indicators, because they are very sensitive to environmental changes caused by human activity. They are closely associated with environmental conditions and vegetation. Most spiders have specific ecological requirements, making them useful indicators of spatial and temporal variation in terrestrial ecosystems (Pearce & Venier 2006). They are important in trophic networks as predators, as well as because of their abundance, biomass and species diversity (Wise 1993, 2006). They feed on all kinds of invertebrates, especially insects, and some little vertebrates and they are eaten by birds, reptiles, amphibians and several groups of mammals.

Spiders in Agroecosystems
In the last decades there has been an important increase in the number of studies focusing on the use of spiders as biological control agents (Riechert and Lockley, 1984, Young and Edwards, 1990; Sunderland, 1999). They are highlighted for their abundance, biomass and species richness and for their participation in the control of phytophagous species, decomposition and pollination.

It has been mentioned that spiders in the field usually consume about one appropriate-sized insect per day (Nyffeler and Benz, 1987), however they will kill many more insects than they consume (Maupin and Riechert, 2001). In conjunction with other natural enemies (parasitoids, pathogens and other predators) spiders may tip the balance in biological control (Sunderland, 1999), particularly those species called “agrobiont” spiders by Luczak (1979). These spiders have life history characteristics that allow them to reach adulthood and reproduce during the main crop vegetation period, exhibiting high dominance in strong abiotically driven and frequently disturbed habitat types, like agroecosystems (Luczak, 1979, Nyffeler and Benz, 1987, Samu and Szinetár, 2002).