Evidence for nanocoulomb charges on spider ballooning silk

We report on three launches of ballooning Erigone spiders observed in a $0.9{\mathrm{m}}^3$ laboratory chamber, controlled under conditions where no significant air motion was possible. These launches were elicited by vertical, downward-oriented electric fields within the chamber, and the motions indicate clearly that negative electric charge on the ballooning silk, subject to the Coulomb force, produced the lift observed in each launch. We estimate the total charge required under plausible assumptions, and find that at least 1.15 nC is necessary in each case. The charge is likely to be nonuniformly distributed, favoring initial longitudinal mobility of electrons along the fresh silk during extrusion. These results demonstrate that spiders are able to utilize charge on their silk to attain electrostatic flight even in the absence of any aerodynamic lift.

Figure 1

Close-up image of a ballooning silk fan observed during activities related to the experiment reported here. (Photo: M. Hutchinson.)

Figure 2

Frequency of two well-documented preballooning behaviors as a function of external plate voltage in the spider test chamber.

Figure 3

Two examples of frames of the videos used for the acceleration measurements. (a) Tiptoeing spider just at the moment of launch, with fine ballooning silk already deployed and extended vertically, as seen by observer although unresolved in the video. (b) Spider in motion, just before leaving the frame 160 ms later.

Figure 4

(a) Electric field estimated by Remcom XFDTD model. (b) Vertical section through the modeled field above the tip of the conductive launch point. (c) The integrated potential through the same section.

Figure 5

(a) Modeled and measured position for the first observed launch, denoted MVI 1407. (b) Modeled and measured speed for MVI 1407 launch. (c) Modeled and measured positions for the second observed launch, denoted MVI 1503. (d) Modeled and measured speeds for MVI 1503. (e) Modeled and measured positions for the float event. (f) Modeled and measured speeds for the float event.

Figure 6

Two SEM images from ballooning silk gathered during the experiment activities reported here. (Credit: E. Morley.)

Figure 7

(a) Vertical profile of Remcom XFDTD simulation of fair-weather APG fields along a simulated plant stem. (b) Horizontal profile through the tip of the same stem.