Characteristics of spider assemblages of subtropical rice paddy fields in the Yaeyama Islands, Japan

Spiders are important natural enemies of rice pests in paddy fields. To estimate their roles, it is essential to understand their functional diversity. However, little is known about the spider fauna of paddy fields in subtropical regions. Here, we investigated spider diversity and species composition in paddy fields in the Yaeyama Islands, in subtropical Japan. We collected 1489 individuals of at least 42 species in 13 families and 7 guilds from rice paddies on Ishigaki, Iriomote, and Yonaguni islands by net sweeping during the first and second crops from 2013 to 2015. The Tetragnathidae (39%), Araneidae (35%), and Thomisidae (18%) were the most abundant families, comprising > 90% of total abundance. Orb web weavers (73%) and ambush hunters (19%) were the most abundant guilds. The most common species were Neoscona theisi (Walckenaer, 1841) (Araneidae) (n = 352), Tetragnatha javana (Thorell, 1890) (Tetragnathidae) (n = 294), and Tetragnatha nitens (Audouin, 1826) (Tetragnathidae) (n = 94). The results show that the species composition of spiders in subtropical paddy fields is more similar to that in tropical paddy fields in Asia than to that in temperate paddy fields in mainland Japan. Ordination analysis showed that the composition of spiders on Ishigaki island varies greatly with season and year. This study makes a valuable contribution to knowledge of the comprehensive diversity of subtropical spiders associated with rice paddy fields in Japan.