Research ArticleECOLOGY

Mechanical spectroscopy of insect swarms

See allHide authors and affiliations

Science Advances  10 Jul 2019:
Vol. 5, no. 7, eaaw9305
DOI: 10.1126/sciadv.aaw9305

Figures

  • Fig. 1 Mean swarm response to an oscillating swarm marker.

    (A) Trajectories (>40 s long) of individual midges (each color corresponding to a different midge) are individually convoluted but remain localized over the ground-based swarm marker (black square). (B) Sketch of our experimental setup. Swarms form inside a plexiglass cube measuring 122 cm on a side and are imaged using three cameras mounted outside the enclosure. The swarm marker (in dark gray) is mounted on a linear stage (in red) that can be oscillated over a range of controlled frequencies and amplitudes along the direction indicated by the white arrows, which we label as the x direction. z increases vertically from the swarm marker (antiparallel to gravity), with the marker itself at z = 0. Midge development tanks (light blue) and four infrared light-emitting diode arrays (yellow; additional arrays on top of the enclosure are not shown) are also shown. (C) Phase-averaged position of the center of the swarm marker XM and the center of mass of the swarm XS. The swarm center of mass tracks the sinusoidal motion of the marker, although with a reduced amplitude and a phase lag. (D) The amplitude of the swarm center-of-mass motion AS as a function of the amplitude of the marker motion AM for two different oscillation frequencies, showing a linear relationship between the two. The shaded area shows the SEM.

  • Fig. 2 Height-dependent swarm response for a fixed amplitude of AM= 84 mm.

    (A) Phase-averaged mean position of laterally averaged slabs of the swarm XS(z,t) at different heights z above the marker. As z increases, the amplitude of the swarm motion decreases. Black solid lines are sinusoidal fits. For clarity, we only show the response for a subset of z values (80, 123, 166, 209, 295, and 338 mm). (B) The amplitude AS(z) of XS(z,t) as a function of z. The shaded area shows the 95% confidence interval, and the red line is an exponential fit. The vertical axis is logarithmic. (C) The phase lag ϕ (in units of π) between XM and XS(z,t) as a function of z. The red line is a linear fit. (D) Vertical profiles of XS(z,t) at four fixed phases of the driving, revealing the shape of the traveling shear wave. Unlike in (A), where each XS(z,t) curve has fixed z but variable t, here, each curve has fixed t but variable z. The horizontal colored lines at the bottom of the figure show the time-dependent position of the swarm marker corresponding to each of the profiles.

  • Fig. 3 Swarm material properties.

    (A) Storage modulus G' as a function of driving frequency, reported for both angular frequency (bottom axis) and linear frequency (top axis), for a fixed amplitude of AM = 84 mm. The solid line is a parabolic fit. (B) Loss modulus G" as a function of frequency for the same data as in (A). The solid line is a linear fit. (C) Dispersion relation relating the shear wave speed c and the driving frequency. For all panels, the shaded areas show the SEM and are the result of averaging over different swarming events.

  • Fig. 4 Response of a swarm model.

    (A) Phase-averaged mean position of laterally averaged slabs of the swarm model XS(z,t) at different vertical distances z from the swarm center, where the oscillating perturbation is applied along x. As z increases, the amplitude of the swarm motion decreases. Black solid lines are sinusoidal fits. The amplitude of the oscillation of the center of attraction is 2, and the frequency of oscillation is 0.65 rad s−1. (B) The amplitude AS(z) of XS(z,t) as a function of z. The shaded area shows the 95% confidence interval. The red line is an exponential fit. The vertical axis is logarithmic. (C) The phase lag ϕ (in units of π) between the oscillation of the swarm center and XS(z,t) as a function of z. The shaded area shows the 95% confidence interval, and the red line is a linear fit. Results are shown for the case where all model parameters (σr, σu, and T) are set to unity in arbitrary units.

  • Fig. 5 Model swarm material properties.

    (A) Storage modulus G' of the swarm model as a function of driving frequency, reported for both angular frequency (bottom axis) and linear frequency (top axis), for a fixed amplitude of 2 and swarm density of 1. The solid line is a parabolic fit. (B) Loss modulus G" as a function of frequency for the same data as in (A). The solid line is a linear fit. For all panels, the shaded areas show the SEM. Results are shown for the case where all model parameters (σr, σu, and T) are set to unity in arbitrary units.

Stay Connected to Science Advances

Navigate This Article