Short and flat grass preferred by adults of the endangered dragonfly Sympetrum pedemontanum elatum (Odonata: Libellulidae)

Sympetrum pedemontanum (Müller in Allioni) (Odonata: Libellulidae) is widely distributed across the Eurasian continent and its neighboring islands. However, the populations of its subspecies S. pedemontanum elatum (Selys) in Japan have been rapidly decreasing with the loss of habitats in rural and suburban areas since the 1970s. For the conservation of this subspecies, which is now listed as endangered in many prefectures, it is important to understand the habitat preferences of the adults. Previous studies indicate that adult males of this species tend to fly on the flat surface of rice paddy fields. Thus, we hypothesized that they preferred short and flat grass. Field experiments in the Sakasegawa River, Hyogo Prefecture, Japan, showed that adult S. p. elatum significantly preferred the trimmed grass of Phragmites japonicus to untreated shaggy grass, regardless of sex. Our results indicate the importance of grass management for the conservation of this species, not only in and around paddy fields but also in fluvial habitats, which are abundant in Japan.