Robber flies track their beetle prey using small movements of movement

By | March 5, 2024

April in the Florida Panhandle. It was hot, humid and a thunderstorm was brewing. But as a recent college graduate, I was relieved to escape my first brutal Minnesota winter. I accompanied my advisor, Paloma Gonzalez-Bellido, on a project that ultimately earned my Ph.D. work. Out in the bushes, my eyes darted with every movement, wary of an insect that likes shiny beads.

Laphria saffron, also known as predatory flies, are fat black and yellow flies. Most of a laphria’s head consists of its large eyes, between which sits a formidable proboscis: a long, tubular mouthpart that can deliver a powerful venom capable of incapacitating prey in an instant.

The photos Paloma showed me before we got there, while beautiful, did not help in my search for the fly. Insects were flying in all directions, their movements blurred, making it impossible to make out details. I only had a split second to figure out if the thing I saw was a laphria, a yellowjacket wasp of the same color, or something completely different.

Despite their relatively crude vision, the flies I searched for are far more adept than I am at detecting the insects they target. Somehow they are able to target their favorite prey: beetles. Based on her field observations last year, Paloma thought they did this by looking for the flash of beetle wings.

If she was right, Laphria has devised an ingenious trick that balances the need for speed, accuracy and specificity. Here are some clues we found to the secrets of their success.

After the flash

Paloma had previously studied other insect predators, such as dragonflies and deadly flies. Their compound eyes do not provide much detail about the visual world, making it possible to trick them into chasing simple beads as if they were their insect prey.

But when Paloma tried the same trick with laphria, they didn’t want to go for the regular black beads. They only chased bright beads.

The only major difference between Laphria and the other predators Paloma had studied is that they are picky eaters. Their favorite prey is beetles. So Paloma and our collaborator, Jennifer Talley, speculated that the reason laphria are attracted to shiny beads is because they reflected light and flashed like a beetle’s bright wings.

In Florida, we tested this idea by replacing the plain black beads with a panel of LED lights that we could program to flash successively at a frequency that matched beetles’ wing beats, which is somewhere between 80 and 120 beats per second. could be. .

In an outdoor enclosure, Paloma placed previously captured robber flies one after the other on a tree trunk. Outside, Jennifer and I checked the LED panel for the tree trunk and the high-speed cameras capturing the action.

The LED pixels flashed in sequence, simulating a moving target. Laphria followed the lights with great interest only when they flashed with the same frequency that beetles flapped their wings.

But even as our first experiments began to confirm the hypothesis, a new puzzle presented itself. How do the flies accurately track their prey?

Unique strategy to track and identify

Before giving chase, all visual predators, including laphria, must carefully track the movements of their prey. While many animals have this ability, what we found in Laphria was, to our surprise, a slightly modified formula compared to other predators. Their strategy allows them to not only accurately track, but also count, the flashes of their prey’s wing movements.

When I watched the high-speed videos of Laphria following the flashing LEDs and real beetles, I noticed that they moved their heads mainly in short bursts called saccades, interspersed with little or no other movements. 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 extent to which the flies moved their heads during each burst depended on the speed of the target and how far it was off-center from the direction the fly was looking.

What our findings told us is that instead of constantly moving their heads to maintain the position of the target in the most sensitive parts of their eyes, Laphria let it pass over their retina and only move when it goes out of focus. We think this strategy helps them count the flashes of the prey’s beating wings, which determines their continued interest.

That is, the laphria know the wingbeat frequency of their tastiest prey and so pay attention to flashes that match it. If the number of flashes matches their expectations, they will continue to follow the target after it has slipped out of the sensitive zone of their eyes.

However, to bring it back into view, they must take into account its speed and the position where they last saw it. Since the size of the saccade corresponds to the speed of the prey, we think the Laphria keeps track of how fast the prey is moving while simultaneously counting the flashes of its wing beats. So once a beetle loses focus, the predator knows how much to move its head to refocus.

Even though people are constantly following moving objects – for example while playing sports such as baseball or tennis or even while watching a bird fly by – it is a complex process. It involves dynamic crosstalk between the visual and muscular systems.

Regardless of the motivation, the goal when visually tracking a target is the same: to train the most sensitive area of ​​the eyes, known as the fovea, on the item in question. Laphria saffron apparently changed that rule so they could learn more about the target. Their customized forecasting strategy allows them to accurately pinpoint and quickly track their very specific nutritional needs.

This article is republished from The Conversation, a nonprofit, independent news organization providing facts and analysis to help you understand our complex world.

It is 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 disclosed no relevant affiliations beyond their academic appointment.

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