Spiders (Arachnida: Araneae) Of Milbridge, Washington County, Maine

Abstract

Adult spiders (N = 6,979) of 19 families, 145 genera, and 302 species (including 4 unknown) were collected from diverse inland, coastal, and offshore habitats of Milbridge, a 6,290-ha minor civil division of the East Coastal BioPhysical Region. Spider species richness per family ranged from 1 (Titanoecidae and Pisauridae) to 89 (Linyphiidae); species richness per genus ranged from 1 to 13, with 88 genera represented by a single species. As expected, the collected taxa were distributed unequally between two basic foraging strategies: 10 families, 98 genera, and 179 species of web spinners; 9 families, 47 genera, and 123 species of hunters.Spider abundances varied widely among taxa; individuals per family ranged from 1 (Titanoecidae and Pisauridae) to 1,691(Lycosidae); individuals per species ranged from 1 (86 species) to 470. Pardosa moesta was the most frequently collected spider. Although total species composition favored web spinners over hunters, more hunters were collected than web spinners, and more female spiders were collected than male spiders, a pattern evident for both web spinners and hunters. Spider sex ratios varied widely among the collected species and were influenced by sampling method, habitat, and season. Pitfall traps yielded more species and more individuals than any other sampling method. Fully 47.0 percent of the inventoried fauna were method-unique species; most were taken by pitfall traps, searches, and sweep nets. Species-faunal compositions among habitats were generally distinct among habitats (QS ≤ 50.0), and included habitat-unique spedies.Species-range extensions include 31 new state records, 6 New England records, and 3 national records. At least 12 invasive species were among the inventoried spiders; 5 were associated with domestic habitats. Based on published and unpublished records from the same biophysical region, total estimated richness is 24 families, 172 genera, and ~ 411 species. Loss of habitat and displacement of native species by invasives pose potential threats to this diverse fauna. COVER PHOTOAraneus orb weaver, courtesy of Lt. Col. Murray Cragin, USAF (retired).