Landing mosquitoes bounce when engaging a substrate

Abstract

In this experimental study we film the landings of Aedes aegypti mosquitoes to characterize landing behaviors and kinetics, limitations, and the passive physiological mechanics they employ to land on a vertical surface. A typical landing involves 1-2 bounces, reducing inbound momentum by more than half before the mosquito firmly attaches to a surface. Mosquitoes initially approach landing surfaces at 0.1-0.6 m/s, decelerating to zero velocity in approximately 5 ms at accelerations as high as 5.5 gravities. Unlike Dipteran relatives, mosquitoes do not visibly prepare for landing with leg adjustments or body pitching. Instead mosquitoes rely on damping by deforming two forelimbs and buckling of the proboscis, which also serves to distribute the impact force, lessening the potential of detection by a mammalian host. The rebound response of a landing mosquito is well-characterized by a passive mass-spring-damper model which permits the calculation of force across impact velocity. The landing force of the average mosquito in our study is approximately 40 [Formula: see text]N corresponding to an impact velocity of 0.24 m/s. The substrate contact velocity which produces a force perceptible to humans, 0.42 m/s, is above 85% of experimentally observed landing speeds.

Figure 1

(a) Photographic landing sequence viewed from above. (b) Experimental setup of flight arena and orthogonally-positioned high-speed video cameras. (c) Three-dimensional displacement plot of a mosquito landing with 2.5 ms between each position marker.

Figure 2

Normal-to-substrate displacement for all 20 analyzed landings. The tracked point on the mosquito is the interface of the proboscis with the head. The final resting position of the tracked point corresponds to $x=0$. First contact of any portion of the mosquito with the landing surface corresponds to $t=0$. Dashed-curves indicate the proboscis is the first member to contact the substrate, while solid lines indicate tarsi initiate contact. Curves are smoothed with a second-order Savitzky–Golay filter at 10% span.

Figure 3

Mosquito landing plots for (a) Temporal normal-to-substrate displacement. (b) Temporal normal-to-substrate velocity. Data in plots (a) and (b) is smoothed with a second-order Savitzky–Golay filter at 10% span. (c) Initial deceleration of mosquito. (d) First contact of proboscis. (e) Collapse of the proboscis with head nearly contacting surface. (f) Maximum bounce displacement. (g) Final stabilization of landing position with eminent wing retraction.

Figure 4

Mosquito landing with proboscis (a) initiating contact with substrate, and deflecting from normal force. (b) Modulus experiment with mosquito proboscis fixed on one end and loaded on free end with a water droplet. (c) Diagram of measured parameters depicting proboscis deflection due to end load.

Figure 5

(a) Mosquito displacement over time for a mosquito standing on the floor of a box vibrating at 50 Hz. The curve is smoothed with a second-order Savitzky–Golay filter at 10% span. (b) Experimental landing data, Fit 1 based on Eq. (6), and Fit 2 from Eq. (7).

Figure 6

The temporal substrate force from Eq. (8) for various landing velocities. Blue and red curves represent the slowest and fastest observed velocities, respectively, while the purple cone denotes the standard deviation around the average observed velocity.