Habitat Distribution and Life History of Araneus Spider Species in the Great Smoky Mountains National Park

Davis, Melinda; Coyle, Frederick

ABSTRACT: Habitat distribution patterns of nine Araneus species were studied by analysing 1,163 1-hr samples from 17 focal sites representing 16 major habitats in the Great Smoky Mountains National Park. Of the five large-bodied diadematus group species, A. nordmanni is common or abundant in 12 of the 16 habitats (ten forest types, heath bald, and high grass bald), A. marmoreus is common or abundant in five habitats (four forest types and high grass bald), A. trifolium is restricted to grass balds, and A. bicentenarius and A. iviei are virtually restricted to (and uncommon in) forest edge and marsh habitats, respectively. In the three forest communities (red oak, northern hardwood, and beech gap) where A. nordmanni and A. marmoreus coexist at high densities, microhabitat segregation exists, at least in the adult stage; nordmanni females use only trees as retreat/web substrates and marmoreus females use only the herbaceous vegetation of tree gaps. This preference for tree gaps means that A. marmoreus is an indicator of forest decline. Of the four small-bodied Araneus species (A. cingulatus, A. miniatus, A. pegnia and A. pratensis), only A. pratensis, which is restricted to grassland, appears to be common or abundant in any habitat. Size frequency histograms of seasonal samples of A. nordmanni and A. pratensis specimens indicate that the former species has a two-year life cycle with eight post-emergent (post-eggsac) instars and the latter has a one-year life cycle with seven post-emergent instars. Spiderlings of A. nordmanni emerge from the egg sac in the spring, develop to post-emergent instar IV, V or VI before overwintering, and then reach adulthood and reproduce during their second summer. Spiderlings of A. pratensis emerge from the egg sac in early summer, develop to the antepenultimate or penultimate instar by winter, and mature and reproduce in the following spring.