Presentation Information
[ACC45-P06]Tree-climbing behavior of winter stoneflies on Mt. Gassan, Yamagata Prefecture, Japan
*Hitomi Uriu1, Nozomu Takeuchi2 (1.Chiba University Graduate School of Science and Engineering, 2.Center for Environmental Remote Sensing Chiba University)
Keywords:
winter stoneflies,Mt. Gassan,snow
Winter stoneflies, wingless aquatic insects, are the insects that are active on snowpack surfaces and belong to the family Capniidae. They can be commonly found in snowy regions across Japan, but are largely affected by the change of snow conditions due to climate warming. After emerging from the stream in which it spent its larval stage, they ascend onto the snow surface and are known to exhibit upstream migratory behavior to reach suitable sites for oviposition. In forested areas, they are frequently observed moving and resting on tree trunks; however, the reason for this tree-climbing behavior remains unclear. The purpose of this study was to investigate the behavior of the snow stonefly in a forest zone on Mt. Gassan, Yamagata Prefecture, and to clarify the factors driving its tree-climbing behavior. Field surveys were conducted from 19–21 March and 25–27 April 2025 in mixed deciduous forests of Japanese beech (Fagus crenata) and larch (Larix spp. ) at elevations of approximately 750–1100 m on Mt. Gassan, Yamagata Prefecture. Time-lapse photography of snowpack and tree trunk surfaces to quantify diurnal cycles of their population and behavior. The winter stoneflies were not observed on larch trees, but only on Japanese beech trees rich in lichens and mosses. Analysis of the time-lapse images showed that their density on the snow surface peaked in the morning, whereas density on tree trunks reached its maximum in the evening. Most of individuals remained stationary on tree trunks for extended periods. Air temperature measured during the investigation peaked around 12:00, showing no clear relationship with changes in stonefly density on tree trunks. Measurements of tree trunk surface temperature showed that tree-climbing behavior was generally observed within a temperature range of approximately 7–11 ℃. Analysis of the directional distribution of stoneflies on tree trunks revealed a tendency for individuals to occupy the side opposite the direction of the sun. These results suggest that the tree-climbing behavior of the snow stonefly may serve the purpose of foraging on lichens present on the surface of Japanese beech trees, and/or of remaining within a temperature range that minimizes thermal stress.