An observational study of ballooning in large spiders: Nanoscale multifibers enable large spiders’ soaring flight

Abstract

The physical mechanism of aerial dispersal of spiders, “ballooning behavior,” is still unclear because of the lack of serious scientific observations and experiments. Therefore, as a first step in clarifying the phenomenon, we studied the ballooning behavior of relatively large spiders (heavier than 5 mg) in nature. Additional wind tunnel tests to identify ballooning silks were implemented in the laboratory. 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. In the wind tunnel tests, as-yet-unknown physical properties of ballooning fibers (length, thickness, and number of fibers) were identified. Large spiders, 16–20 mg Xysticus spp., spun 50–60 nanoscale fibers, with a diameter of 121–323 nm. The length of these threads was 3.22 ± 1.31 m (N = 22). 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. 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. This regime is highly correlated with lower wind speeds. This coincides well with the fact that spiders usually balloon when the wind speed is lower than 3 m s−1.

Dispersal and life-history traits in a spider with rapid range expansion

“…2c). This combination of ventilators ensured a wind speed of 0.5-1.5 m/s at the tip of the ballooning units, in line with data on ballooning under natural conditions [42,43]. The ballooning set-up received artificial light from standard ceiling lamps.…”

“…Spiders display a unique dispersal behaviour, which can be studied in controlled conditions in the lab [41]; they drift with air currents during a behaviour called "ballooning" after displaying unique behaviours prior to the dispersal event. Ballooning activity depends on environmental conditions such as temperature and wind velocity [42,43] and on the body size of the disperser; offspring disperse after hatching in larger species, whereas adult stages may balloon in small species.…”

Evidence for nanocoulomb charges on spider ballooning silk

“…Thus a crucial question arising from these results is whether spiders modify their behavior and silk extrusion process to adapt to lower fields. Certainly one approach is to use longer silk, for example ballooning silks up to 3 m long have been observed in natural ballooning of larger spiders [12]. Assuming a linear increase in total charge, an order of magnitude more lift may be possible by this method alone for the spiders considered here.…”

“…These models do yield lift in numerical simulations spider ballooning, but still appear to require sig-nificant upward components to the local wind velocity distribution; whether actual wind momentum spectra provide the required distributions is still unproven, particularly for takeoff conditions. Even so, recent detailed observations of spider ballooning analyzed exclusively in terms of aerodynamic forces [12] provide plausible evidence that larger spiders can use multithread fans of relatively long silk, 3 m or more, to achieve takeoff and buoyancy in low winds within a certain turbulence regime. An example of multithread silk extrusion, shown in close proximity to the spinneret in a Linyphiid spider, is shown in Fig.…”

Sex differences in spiders: from phenotype to genomics

“…Solitary spiders disperse as small spiderlings via a mechanism called ballooning. The spiders become airborne by releasing silk threads under favorable certain environmental conditions such that the drag will lift them (Cho et al 2018;Weyman 1993). Ballooning and short distance dispersal can be triggered by density and resource availability (Puzin et al 2019) and vary individually (Johnson et al 2015) for example due to paternal effects (Mestre and Bonte 2012).…”