July 11 – Are Robber Flies Similar to Humans? – Guest Blog by V. Chilcoat

The vision of a robber fly is both miraculous and breath-taking. How can one tiny insect occupy such advanced vision? Their sight is one extreme example on how organisms have evolved to become amazing predators. The Ohio Bee Survey (2020 to the pres.) aims to identify and enumerate the bee species of Ohio. Bycatch specimens from our passive water bowl traps contain a variety of insects, including Asilidae, also known as robber flies. These insects are predators of flies, wasps, beetles, moths, and many other arthropods.

Example of a robber fly with prey that was collected in one of our bowl traps by H. Carpenter.

In addition to working as a research assistant in Dr. Goodell’s lab, I am conducting a research project to analyze habitat drivers of Asilidae abundance and diversity. I will examine how their abundance changes with landscape-scale habitat-quality. I will also test the hypothesis that robber fly abundance is positively correlated with that of two of their prey taxa: —bees (Anthophila) and hover flies (Syrphidae).

The robber fly predatory behavior is intriguing in that they use visual evolutionary adaptations that allow them to track and capture prey efficiently. This ocular capability is known to be comparable to humans as their eyesight functions similarly. To track their prey successfully, robber flies use an amazing angle and acceleration strategy. These insects use a “lock-on” targeting system in which they fly parallel alongside their prey and employ a constant bearing angle (CBA) strategy for their flight. An analogy to the CBA system of prey capture is found in the method used by two relay runners in the act of passing a baton successfully between them. A waiting runner will begin to accelerate in parallel to the approaching teammate— to facilitate baton transfer with as little loss of speed as possible. Asilids use this method to pursue and then grab its prey in midflight. This model allows the predator to respond to unexpected changes in their prey’s speed and position. An experiment was performed by a team of researchers, Wardill et al., who looked at the predatory behavior (see video below). A mechanism, a fishing rod with a bead on the end to represent the prey, was used to observe the pathway that the Asilidae takes when capturing their meal. They travel parallelly with the other insect until the point of interception to finally seize their snack. Interestingly, humans, dragon flies, and fish also use the CBA model to keep the view of their target constant over time, avoiding uncertainty. This method that robber flies and other animals use provides a reliable mechanism to catch their prey (Rothkopf and Schrater 2013).

The predatory strategy of Asilidae uses multiple types of visual cues, for example, optical tau and binocular cues. The optical tau is the ratio of an object’s diameter over its varying distance. These visual processes enhance the performance of reaching and grasping movements which is relative to the vision in humans. This allows the insect to obtain the right cues on when to approach their prey. An image of the structure of an asilid eye and body caught within the bycatch of the Ohio Bee Survey is displayed within Figure 2. It is amazing how the evolution of asilid eyes facilitate a mirror image of the functional aspects within human vision.

Figure 2. Asilidae collected by Cameron Svoboda on August 5, 2020 at Blacklick Metropark. (Photos by Vanessa Chilcoat)

Information about Asilidae was from Wardill et al. (2017) and Rothkopf & Schrater (2013).

Wardill, T. J., Fabian, S. T., Pettigrew, A. C., Stavenga, D. G., Nordström, K., & Gonzalez-Bellido, P. T. (2017). A Novel Interception Strategy in a Miniature Robber Fly with Extreme Visual Acuity. Current Biology, 27(6), 854–859. https://doi.org/10.1016/j.cub.2017.01.050

Rothkopf, C., & Schrater, P. (2013). Optimally adapting heuristics: humans quickly abandon the constant bearing angle strategy. Journal of Vision, 13(9), 122–122. https://doi.org/10.1167/13.9.122

Note from MaLisa on weekly progress:

We sorted 7 kits last week: M. Schilling (Clermont), J. Kutzley (Madison), A. Lighthiser (Licking), P. Siebert (Warren), J. Driscoll (Lorain), C. Beveridge (Columbiana), and K. McCoy (Fayette). The interesting bycatch from these samples will be shared at a later date. We are now over 46,000 bees pinned! We only have 20 kits left to sort and then we switch full time to identification.

We also got a new record number of bees in a single day at a single site! Coming in at an average of 27 bees per bowl on August 5th, M. Schilling’s sample has blown away the previous daily record (451 bees, also Aug 5 at Cedar Bog by J. Page) for a whopping 623 bees! So clearly something was happening on August 5th as we are seeing similar spikes, though not as dramatic, with other samples. It took Connor 3 hours just to pin all 623 of the bees from this one sample day.

3 hours of gluing and pinning later, and this is what we have to show for the record breaking sample. They still each need individual labels added to each specimen before we can identify them. So plenty of work left to do.