Another takeoff method is called “rafting,” in which spiders release the ballooning lines from a hanging position, relying on their drag line (see S3 Fig). This is known as a “tiptoe” takeoff (see S1 and S2 Figs). They release a single or a number of silks in the wind current and wait until a sufficient updraft draws their body up in the air. If spiders perceive appropriate weather conditions for ballooning, they climb up to the highest position of a blade of grass or a branch of a tree and raise their abdomen as if standing on their tiptoes, in order to position the abdomen at the highest level, before spinning the ballooning lines. There are 2 representative takeoff methods in ballooning flight: “tiptoe” and “rafting”. Some spiders from different families, such as Linyphiidae (sheet-weaver spiders), Araneidae (orb-weaving spiders), Lycosidae (wolf spiders), and Thomisidae (crab spiders), can disperse aerially with the help of their silks, which is usually called ballooning behavior. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Ĭompeting interests: The authors have declared that no competing interests exist. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.ĭata Availability: All relevant data are within the paper and its Supporting Information files.įunding: Elsa-Neumann-Scholarship (grant number T61004). Received: OctoAccepted: Published: June 14, 2018Ĭopyright: © 2018 Cho et al. PLoS Biol 16(6):Īcademic Editor: Laura Miller, University of North Carolina at Chapel Hill, United States of America This work represents the most rigorous investigation of spider ballooning to date and will inspire future research on the subject.Ĭitation: Cho M, Neubauer P, Fahrenson C, Rechenberg I (2018) An observational study of ballooning in large spiders: Nanoscale multifibers enable large spiders’ soaring flight. This may explain why spiders show the ballooning behavior at a low wind speed, as the updraft frequently exists in the low-speed regime of the fluctuating wind flows. From our wind measurements, we suggest that spiders use the organized updraft current in the turbulent wind. Using this nano/microscale fluid dynamics, spiders can become airborne with a light updraft. In the air current, these nanoscale fibers are governed by low Reynolds number fluid dynamics, which means that the viscous force of the air is much more dominant than the inertial force of the air. Crab spiders use tens of nanoscale fibers for their aerial dispersal. These quantitative values can explain large spiders’ ballooning behaviors. From our observations in the field and in the laboratory using a wind tunnel, we have characterized the heretofore unknown physical properties of spiders’ ballooning silks. However, little is known about the ballooning mechanism of spiders, due to the difficulty of observing the ballooning silks and little awareness of spiders’ ballooning flight itself. This coincides well with the fact that spiders usually balloon when the wind speed is lower than 3 m s −1.Īerial dispersal of spiders, which is known as “ballooning,” enables spiders’ wide range of dissemination-sometimes transoceanic. This regime is highly correlated with lower wind speeds. Additionally, in line with previous research on turbulence in atmospheric boundary layers and from our wind measurements, it is hypothesized that spiders use the ascending air current for their aerial dispersal, the “ejection” regime, which is induced by hairpin vortices in the atmospheric boundary layer turbulence. These physical properties of ballooning fibers can explain the ballooning of large spiders with relatively light updrafts, 0.1–0.5 m s −1, which exist in a light breeze of 1.5–3.3 m s −1. The length of these threads was 3.22 ± 1.31 m ( N = 22). Large spiders, 16–20 mg Xysticus spp., spun 50–60 nanoscale fibers, with a diameter of 121–323 nm. In the wind tunnel tests, as-yet-unknown physical properties of ballooning fibers (length, thickness, and number of fibers) were identified. From our observation, it seems obvious that spiders actively evaluate the condition of the wind with their front leg (leg I) and wait for the preferable wind condition for their ballooning takeoff. Additional wind tunnel tests to identify ballooning silks were implemented in the laboratory. Therefore, as a first step in clarifying the phenomenon, we studied the ballooning behavior of relatively large spiders (heavier than 5 mg) in nature. The physical mechanism of aerial dispersal of spiders, “ballooning behavior,” is still unclear because of the lack of serious scientific observations and experiments.
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