April in the Florida Panhandle. The weather was hot, humid, and a storm was lurking. But I was relieved to escape my first brutal Minnesota winter as a new graduate student. I was accompanying my advisor, Paloma Gonzalez-Bellido, on a project that would dominate my PhD. work. In the bushes, my eyes were alerted to an insect that liked bright beads with every movement.
Laphria saffronAlso known as robber flies, they are chunky black and yellow flies. Most of Laphria’s head consists of large eyes, and between these eyes is a formidable proboscis; This is a long, tubular mouthpart that can deliver a powerful venom that can incapacitate prey in a heartbeat.
The photos Paloma showed me before I got there, although striking, were not helpful at all in my search for the fly. There were insects flying in every direction, their movements blurred, making it impossible to make out any details. I only had a few seconds to figure out whether what I was seeing was a laphria, a similarly colored yellowjacket bumblebee, or something else entirely.
Despite their relatively crude appearance, the flies I seek out are far more adept than I am at selecting the insects they target. They are somehow able to focus on their chosen prey, insects. Based on field observations last year, Paloma thought they did this by looking for the insect’s wing flash.
If he’s right, Laphria has found an ingenious trick that balances the need for speed, accuracy, and specificity. Here are some clues we found about the secrets of their success.
After the flash
Paloma had previously studied other predatory insects, such as dragonflies and killer 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 their prey were insects.
But when Paloma tried the same sleight of hand on laphria, they did not choose ordinary black beads. They were just after clear beads.
A key difference between Laphria and the other predators Paloma studied is that they are picky eaters. Their preferred prey are insects. Paloma and our collaborator Jennifer Talley suggested that the reason laphria is attracted to shiny beads is because they reflect light and sparkle like an insect’s clear wings.
In Florida, we tested this idea with an LED light panel that, by replacing plain black beads, we could program to flash sequentially at a frequency that matches the insects’ wingbeats (which can be between 80 and 120 beats per second). .
In an outdoor enclosure, Paloma placed previously caught robber flies one after another on a log. Outside, Jennifer and I were checking out the LED panel in front of the log and the high-speed cameras recording the action.
LED pixels flashed sequentially, simulating a moving target. Laphria followed the lights with great interest as they flashed only at the frequency at which insects flap their wings.
But just as our initial experiments began to confirm the hypothesis, a new conundrum presented itself. How do flies accurately track their prey?
Unique strategy to track and identify
All visual hunters, including Laphria, need to accurately track their prey’s movements before beginning the chase. Although many animals have this ability, what we found in Laphria was a slightly modified formula compared to other predators. Their strategy allows them to not only accurately track but also count the flashes caused by their prey’s wing movements.
When I looked at high-speed videos of laphria following flashing LEDs and real bugs, I noticed that they primarily moved their heads in short bursts, called twitches, interspersed with little or no movement. These twitches are extremely fast, lasting less than 40 milliseconds, and the interval between them is only slightly longer. To the naked eye, this appears to be continuous motion, but our high-speed videos show otherwise. The degree to which the flies moved their heads during each burst depended on the speed of the target and how far off center the fly was from the direction of gaze.
What our findings tell us is that instead of constantly moving their head to maintain the target’s position in the most sensitive parts of their eyes, the labyrinth allows it to pass over the retina and only moves when it goes out of focus. We think this strategy helps the prey count the flashes of their beating wings, which determines their continued interest.
So Laphrias know the wing-flapping frequency of their most delicious prey, and so they pay attention to matching lights. If the flash count matches their expectations, they will continue to track the target after it moves beyond the sensitive area of their eyes.
But to bring it back into focus, they need to take into account its speed and the location where they last saw it. Because the size of the twitch matches the speed of the prey, we think the laphria is tracking how fast the prey is moving while also counting flashes from wing beats. So when an insect goes out of focus, the predator knows how far it needs to move its head to refocus.
Although humans track moving objects all the time (for example, while playing sports like baseball or tennis, or simply watching a bird fly), it is a complex process. It involves dynamic cross-talk between the visual and muscular systems.
Whatever the motivation, the goal is the same when visually tracking a target; training the most sensitive area of the eyes, known as the fovea, on the object of interest. Laphria saffron It looks like they changed this rule to get more information about the target. Their customized predictive strategy allows them to accurately identify and quickly track very specific nutritional needs.
This article is republished from The Conversation, an independent, nonprofit news organization providing facts and authoritative analysis to help you understand our complex world. Written by: Siddhant Pusdekar, University of Minnesota
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Siddhant Pusdekar does not work for, consult, own shares in, or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond his academic duties.