DOI: 10.25377/sussex.31069726.v1
title: Research data for Predation via motion parallax in one of two gleaning insects

description: These datasheets relate to: Rossoni, S., Sumner, M.E., Stavenga, D.G., Fabian, S.T., Supple, J.A., Gonzalez-Bellido, P.T. (2026). Predation via motion parallax in one of two gleaning insects. <i>J. Exp. Biol</i>.<br><b>Abstract</b>A predator’s survival is highly dependent on correctly deciding whether to attack potential prey. Pursuit predators, for example, can estimate the size of a moving target from the ratio between its angular speed and size. Such heuristic rules are not available, however, when ambushing stationary prey. Here, we investigate how pixie robber flies (<i>Psilonyx annulatus</i>) and damselflies (<i>Ischnura posita</i>) hunt stationary prey using different sensory strategies, relating to their marked differences in eye morphology. We show that pixie robber flies assess prey using whole-body translational movements. During this assessment, the prey is outside of the pixie robber fly’s stereopsis range, yet attacks are launched from a distance dictated by absolute, not angular, prey size. These findings suggest that pixie robber flies use motion parallax to infer three-dimensional cues, such as prey distance and/or size, before attacking. Motion parallax may be particularly suitable for pixie robber flies as they hunt in cluttered, low-lighting conditions and have a small size, making it difficult for potential prey to detect their movement, even in close proximity. Damselflies likely rely on alternative processes to assess prey, as translational movements are absent in the assessment phase.<br><br><b>Description of the data and file structure</b><br>These spreadsheets contain the data used in the paper. The first spreadsheet contains the data comparison between predatory attacks of fragile forktail damselflies and ringed pixie robber flies to real D. melanogaster. The second spreadsheet contains data related to the predatory attacks of ringed pixie robber flies to images of D. melanogaster of different lengths, all in colour and on blank backgrounds. Each row on both spreadsheets represents an individual attack sequence.<b>Files & Variables</b><b>File:</b> Rossonietal2026_JEB_Robberfly_damselfly.csv<b>Description:</b> spreadsheets containing data from the attacks of either pixie robber flies or damselflies to real D. melanogaster.<br><br><b>Variables:</b><br>- fly: which predator performed the hunt (damselfly or pixie robber fly)- assessment_onset_distance_mm: distance between predator and prey (in mm) at assessment onset- assessment_duration_ms: duration of the assessment (in ms)- assessment_mean_speed_m/s: average flight speed during the assessment (in m/s)- assessment_straightness_index: straightness index of the assessment- attack_onset_distance_mm: distance between predator and prey (in mm) at attack onset- attack_duration_ms: duration of the attack (in ms)- attack_max_speed_m/s: maximum flight speed during the attack (in m/s)- attack_straightness_index: straightness index of the attack<br><b>File</b>: <i>Rossonietal2026_JEB_Preyimage_sizes.csv</i><b>Description:</b> spreadsheets containing data from the attacks of pixie robber flies to images of D. melanogaster of different length.<b>Variables:</b>- prey_length_mm: length of prey image shown (in mm)- assessment_centroid_angsize_deg: angular size of the prey image from the centroid of the assessment (in degrees)- assessment_mean_speed_m/s: average flight speed during the assessment (in m/s)- assessment_duration_ms: duration of the assessment (in ms)- assessment_straightness_index: straightness index of the assessment- assessment_movement_range_mm: movement range of the assessment (in mm)- attack_onset_distance_mm: distance between predator and prey (in mm) at attack onset- attack_onset_angsize_deg: angular size of the prey image at attack onset (in degrees)<b>Code/software</b>Files are uploaded as comma separated value (csv) format. Files have been viewed and analysed by the authors using Microsoft Excel, MATLAB (version R2024a), and R studio (version 2024.04.2).