Search

The ability to visualize small moving objects is vital for the survival of many animals, as these could represent predators or prey. For example, predatory insects, including dragonflies, robber flies and killer flies, perform elegant, high-speed pursuits of both biological and artificial targets. Many non-predatory insects, including male hoverflies and blowflies, also pursue targets during territorial or courtship interactions. To date, most hoverfly pursuits have been studied outdoors. To investigate hoverfly (Eristalis tenax) pursuits under more controlled settings, we constructed an indoor arena that was large enough to encourage naturalistic behavior. We presented artificial beads of different sizes, moving at different speeds, and filmed pursuits with two cameras, allowing subsequent 3D reconstruction of the hoverfly and bead position as a function of time. We show that male E. tenax hoverflies are unlikely to use strict heuristic rules based on angular size or speed to determine when to start pursuit, at least in our indoor setting. We found that hoverflies pursued faster beads when the trajectory involved flying downwards towards the bead. Furthermore, we show that target pursuit behavior can be broken down into two stages. In the first stage, the hoverfly attempts to rapidly decreases the distance to the target by intercepting it at high speed. During the second stage, the hoverfly's forward speed is correlated with the speed of the bead, so that the hoverfly remains close, but without catching it. This may be similar to dragonfly shadowing behavior, previously coined ‘motion camouflage’.

The miniature robber fly Holcocephala fusca intercepts its targets with behaviour that is approximated by the proportional navigation guidance law. During predatory trials, we challenged the interception of H. fusca performance by placing a large object in its potential flight path. In response, H. fusca deviated from the path predicted by pure proportional navigation, but in many cases still eventually contacted the target. We show that such flight deviations can be explained as the output of two competing navigational systems: pure-proportional navigation and a simple obstacle avoidance algorithm. Obstacle avoidance by H. fusca is here described by a simple feedback loop that uses the visual expansion of the approaching obstacle to mediate the magnitude of the turning-away response. We name the integration of this steering law with proportional navigation ‘combined guidance’. The results demonstrate that predatory intent does not operate a monopoly on the fly's steering when attacking a target, and that simple guidance combinations can explain obstacle avoidance during interceptive tasks.

Under strong selective pressure for survival, image-forming vision set off an ongoing predatory arms race 500 million years ago. Since then, and particularly so in the arthropods, predatory behavior has driven a myriad of eye adaptations that increase visual performance. In this review, we provide examples of how different arthropod predators have achieved improvements in key visual features such as spatial and temporal resolution of their retina. We then describe morphological, neural and behavioral strategies used by animals in this group to gather crucial information about the prey, such as its distance, velocity and size. We also highlight the importance of head and body tracking movements to aid in categorizing the potential prey, and briefly mention the ongoing work on the sensorimotor transformations necessary for target interception.

Mantis shrimp strikes are one of the fastest animal movements, despite their occurrence in a water medium with viscous drag. Since the strike is produced by a latch-mediated spring-actuated system and not directly driven by muscle action, we predicted that strikes performed in air would be faster than underwater as a result of reduction in the medium's drag. Using high-speed video analysis of stereotyped strikes elicited from Squilla mantis, we found the exact opposite: strikes are much slower and less powerful in air than in water. S. mantisstrikes in air have a similar mass and performance to latch-mediated spring-actuated jumps in locusts, suggesting a potential threshold for the energetics of a 1–2 g limb rotating in air. Drag forces induced by the media may be a key feature in the evolution of mantis shrimp strikes and provide a potential target for probing the braking system of these extremely fast movements.

When aiming to capture a fast-moving target, animals can follow it until they catch up, or try to intercept it. In principle, interception is the more complicated strategy, but also more energy efficient. To study whether simple feedback controllers can explain interception behaviours by animals with miniature brains, we have reconstructed and studied the predatory flights of the robber fly Holcocephala fuscaand killer fly Coenosia attenuata. Although both species catch other aerial arthropods out of the air, Holcocephalacontrasts prey against the open sky, while Coenosiahunts against clutter and at much closer range. Thus, their solutions to this target catching task may differ significantly. We reconstructed in three dimensions the flight trajectories of these two species and those of the presented targets they were attempting to intercept. We then tested their recorded performances against simulations. We found that both species intercept targets on near time-optimal courses. To investigate the guidance laws that could underlie this behaviour, we tested three alternative control systems (pure pursuit, deviated pursuit and proportional navigation). Only proportional navigation explains the timing and magnitude of fly steering responses, but with differing gain constants and delays for each fly species. Holcocephalauses a dimensionless navigational constant of N≈ 3 with a time delay of ≈28 ms to intercept targets over a comparatively long range. This constant is optimal, as it minimizes the control effort required to hit the target. In contrast, Coenosiauses a constant of N≈ 1.5 with a time delay of ≈18 ms, this setting may allow Coenosiato cope with the extremely high line-of-sight rotation rates, which are due to close target proximity, and thus prevent overcompensation of steering. This is the first clear evidence of interception supported by proportional navigation in insects. This work also demonstrates how by setting different gains and delays, the same simple feedback controller can yield the necessary performance in two different environments.