Highlights • Holcocephala fusca robber flies capture prey with a constant bearing angle strategy • The approach is proactively altered to “lock-on” on to prey within 29 cm distance • The retina spatial resolution is 0.28°, but the object detection threshold is 0.13° • The fly’s stereopsis range is estimated to be ~26 cm eTOC blurb Robber flies are aerial predators. Here, Wardill and Fabian et al. show that the tiny robber fly Holcocephala fusca attacks a detected prey reactively, but proactively changes its speed and direction when the prey is within 30 cm. They also show that the very small object detection threshold of 1.3º is supported by a striking visual fovea Data included here is the supplemental data figures and main figures. As the raw dataset is over 10 TB it cannot be offered here or elsewhere. Please contact the authors for obtaining such volumes of data.