How Ants Use Vision When Homing BackwardSebastian Schwarz 5, Michael Mangan 5, Jochen Zeil, Barbara Webb, Antoine Wystrach 6, Antoine Wystrach 5Co-first author6Lead ContactPublished Online: January 19, 2017Publication stage: In Press Corrected ProofOpen AccessDOI: http://dx.doi.org/10.1016/j.cub.2016.12.019Open access funded by Engineering and Physical Sciences Research CouncilArticle Info Publication HistoryPublished: January 19, 2017 Accepted: December 9, 2016 Received in revised form: November 10, 2016 Received: September 26, 2016User LicenseCreative Commons Attribution (CC BY 4.0)Highlights Backward-walking ants rely on celestial but not terrestrial cue memories Correction of direction based on terrestrial cues occurs after peeking forward The retrieved direction can be transferred into a compass frame of reference Ants can decouple their travel direction from their body orientationSummaryAnts can navigate over long distances between their nest and food sites using visual cues [ 1, 2 ]. Recent studies show that this capacity is undiminished when walking backward while dragging a heavy food item [ 35 ]. This challenges the idea that ants use egocentric visual memories of the scene for guidance [ 1, 2, 6 ]. Can ants use their visual memories of the terrestrial cues when going backward? Our results suggest that ants do not adjust their direction of travel based on the perceived scene while going backward. Instead, they maintain a straight direction using their celestial compass. This direction can be dictated by their path integrator [ 5 ] but can also be set using terrestrial visual cues after a forward peek. If the food item is too heavy to enable body rotations, ants moving backward drop their food on occasion, rotate and walk a few steps forward, return to the food, and drag it backward in a now-corrected direction defined by terrestrial cues. Furthermore, we show that ants can maintain their direction of travel independently of their body orientation. It thus appears that egocentric retinal alignment is required for visual scene recognition, but ants can translate this acquired directional information into a holonomic frame of reference, which enables them to decouple their travel direction from their body orientation and hence navigate backward. This reveals substantial flexibility and communication between different types of navigational information: from terrestrial to celestial cues and from egocentric to holonomic directional memories.Keywords:insects, ants, navigation, egocentric memories, directional frame of reference, holonomic, backward motion, landmarks, celestial compassReceived: September 26, 2016; Received in revised form: November 10, 2016; Accepted: December 9, 2016; Published: January 19, 2017 2016 The Author(s). Published by Elsevier Ltd.FREE PDF: Current Biology Water-driven actuation of Ornithoctonus huwena spider silk fibersShuyuan Lin1,2, Jia Zhu3, Xinming Li4, Yang Guo5, Yaopeng Fang2,6, Huanyu Cheng3 more...Affiliations1State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China2Center for Nano and Micro Mechanics, Tsinghua University, Beijing 100084, China3Department of Engineering Science and Mechanics, Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA4Department of Electronic Engineering, The Chinese University of Hong Kong, Hong Kong, China5Institute of Biomechanics and Medical Engineering, Tsinghua University, Beijing 100084, China6School of Aerospace Engineering, Tsinghua University, Beijing 100084, Chinaa)Authors to whom correspondence should be addressed. Electronic addresses: hongweizhu@tsinghua.edu.cn