by April in the Florida Panhandle. It was hot, humid, and a thunderstorm was lurking. But as a freshman graduate student, I was relieved to escape my first brutal Minnesota winter. I was with my advisor, Paloma Gonzalez-Bellido, on a project that would dominate my Ph.D. work. Out in the scrubland, my eyes were watching for every movement, on the alert for insects that like shiny beads.
Laphria saffrana, also known as robber flies, are black and yellow chunk flies. Most of the head of a laphria consists of large eyes, and between them sits a magnificent proboscis – a long, tubular mouth that can deliver strong venom that can incapacitate prey in a heartbeat.
The photos that Paloma showed me before we got there, although stunning, were of no help when we were looking for the flight. Insects were flying in all directions, their movements blurred, making it impossible to pick out any details. I only had a split second to figure out if what I was seeing was a laphria, a yellow jacket wasp of the same color, or something else entirely.
Despite their rather crude vision, the flies I’ve been looking for are much more adept at picking out the insects they’re targeting. Somehow they can zero in on their prey of choice: beetles. Based on her field observations the previous year, Paloma thought they did this by looking for the flash of a beetle’s wings.
If she was right, laphria hit an intellectual trick that balances the need for speed, accuracy and specificity. Here are some of the tips we’ve found on the secrets to success.
After the flash
Paloma had previously studied other predatory insects such as dragonflies and killer flies. Their compound eyes provide little detail about the visual world, allowing them to be lured into pursuing simple beads as if they were prey insects.
But when Paloma tried her hand at laphria, they wouldn’t go for the regular black beads. They only wore clear beads.
The one important difference between laphria and the other predators studied by Paloma is that they are picky eaters. Beetles are their prey of choice. Therefore, Paloma and our colleague, Jennifer Talley, speculated that the reason laphria are attracted to shiny beads is because they reflect light and are flashing like the bright wings of a beetle.
In Florida, we tested this idea by swapping out the simple black beads for a panel of LED lights that we could program to flash at a frequency to match the beat of a beetle’s wings, which can range from 80 to 120 beats. per second. .
In an outdoor enclosure, Paloma placed previously captured robber flies one after the other on a log. Outside, Jennifer and I controlled the LED panel in front of the log and the high-speed cameras that captured the action.
The LED pixels flashed in sequence, simulating a moving target. Laphria only eagerly tracked the lights when they flashed at the same frequency as the beetles beat their wings.
But even as our initial experiments began to confirm the hypothesis, a new answer emerged. How do the flies accurately track their prey?
A unique strategy to track and identify
Before chasing, all visual predators, including lapwings, must accurately track the movements of their prey. Although many animals have this ability, what we found in laphria, which surprised us, was a slightly tweaked formula compared to other predators. Their strategy allows them to not only precisely track but also count those flashes from the wing movements of their prey.
When I watched the high-speed videos of laphria tracking the flashing lights and the actual beetles, I noticed that they mainly moved their heads in short bursts, called saccades, interspersed with little or no movement on any other. These saccades are extremely fast, lasting less than 40 milliseconds, and the time between them is only slightly longer. To the naked eye, this looks like continuous motion, but our high-speed videos show otherwise. The amount that the flies moved their heads during each burst depended on the speed of the target and how far from the center it was from the direction of flight.
What our results told us is that instead of moving their heads continuously to keep the position of the target within the most sensitive parts of their eyes, laphria let it pass over their retina, moving only when it slips it’s out of focus. We think that this strategy helps them to count the wing flashes of the prey, which determines their continued interest.
That is to say that the laphria know the wingbeat frequency of their most delicious prey and therefore pay attention to the flashes that match. If the flash count matches their expectations, they will continue to track the target after it slips out of their eye’s sensitive zone.
To target him back, however, they must account for his speed and where they last saw him. Because the size of the saccade matches the speed of the prey, we think that the laphria is keeping track of how fast the prey is moving and at the same time counting the flashes from its wings. So, when a beetle slips out of focus, the predator knows how much to move its head to refocus.
Although people track moving objects all the time – such as when playing sports such as basketball or tennis or even when watching a bird fly by – it’s a complex process. It involves a dynamic cross-talk between the visual and muscular systems.
Regardless of the stimulus, the goal is the same as visually tracking a target – to train the most sensitive zone of the eye, called the fovea, on the item of interest. Laphria saffrana they seem to have tweaked that rule so they can learn more about the target. Their customized predictive strategy allows them to accurately pinpoint their specific nutritional needs and quickly pursue them.
This article is republished from The Conversation, a non-profit, independent news organization that brings you reliable facts and analysis to help you make sense of our complex world. It was written by: Siddhant Pusdekar, University of Minnesota
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Siddhant Pusdekar does not work for, consult with, own shares in or receive funding from any company or organization that would benefit from this article, and has not disclosed any relevant connections beyond their academic appointment.
