Repository logo

The Killer Fly Hunger Games: Target Size and Speed Predict Decision to Pursuit.

Change log


Wardill, Trevor J 
Knowles, Katie 
Barlow, Laura 
Tapia, Gervasio 
Nordström, Karin 


Predatory animals have evolved to optimally detect their prey using exquisite sensory systems such as vision, olfaction and hearing. It may not be so surprising that vertebrates, with large central nervous systems, excel at predatory behaviors. More striking is the fact that many tiny insects, with their miniscule brains and scaled down nerve cords, are also ferocious, highly successful predators. For predation, it is important to determine whether a prey is suitable before initiating pursuit. This is paramount since pursuing a prey that is too large to capture, subdue or dispatch will generate a substantial metabolic cost (in the form of muscle output) without any chance of metabolic gain (in the form of food). In addition, during all pursuits, the predator breaks its potential camouflage and thus runs the risk of becoming prey itself. Many insects use their eyes to initially detect and subsequently pursue prey. Dragonflies, which are extremely efficient predators, therefore have huge eyes with relatively high spatial resolution that allow efficient prey size estimation before initiating pursuit. However, much smaller insects, such as killer flies, also visualize and successfully pursue prey. This is an impressive behavior since the small size of the killer fly naturally limits the neural capacity and also the spatial resolution provided by the compound eye. Despite this, we here show that killer flies efficiently pursue natural (Drosophila melanogaster) and artificial (beads) prey. The natural pursuits are initiated at a distance of 7.9 ± 2.9 cm, which we show is too far away to allow for distance estimation using binocular disparities. Moreover, we show that rather than estimating absolute prey size prior to launching the attack, as dragonflies do, killer flies attack with high probability when the ratio of the prey's subtended retinal velocity and retinal size is 0.37. We also show that killer flies will respond to a stimulus of an angular size that is smaller than that of the photoreceptor acceptance angle, and that the predatory response is strongly modulated by the metabolic state. Our data thus provide an exciting example of a loosely designed matched filter to Drosophila, but one which will still generate successful pursuits of other suitable prey.



Animals, Decision Making, Insecta, Photic Stimulation, Predatory Behavior, Probability, Size Perception, Spatial Behavior, Time Factors, Time Perception, Video Recording

Journal Title

Brain Behav Evol

Conference Name

Journal ISSN


Volume Title



S. Karger AG
Biotechnology and Biological Sciences Research Council (BB/L024667/1)
This work was funded the Air force Office of Scientific Research (FA9550-10-0472 to Prof. Robert Olberg). An Isaac Newton Trust / Wellcome Trust ISSF / University of Cambridge Joint Research Grant to Gonzalez-Bellido. BBSRC TO TREVOR WARDILL The Swedish Research Council (2012-4740) to Nordström and a Shared Equipment Grant from the School of Biological Sciences (U. of Cambridge).