Why Those Pesky Flies Almost Always Outwit You

Flies can thank their quick, sophisticated eyesight and certain neural quirks for their ability to evade blows with such speed and agility.

Our laboratory investigation insect flight and visionwith the goal of discovering how these tiny creatures can process visual information to perform tricky behaviors, like escaping your swatter so quickly.
Flies have compound eyes. Rather than collecting light through a single lens that does the whole image — the strategy of human eyes — flies form images constructed from multiple facets, many individual lenses that focus incoming light onto clusters of photoreceptors, the light-sensitive cells in their eyes. Essentially, each facet produces an individual pixel of fly vision.
A fly’s world is quite low resolution, as small heads can only hold a limited number of facets — usually hundreds to thousands — and there’s no easy way to narrow down their blurry vision to the millions of pixels people actually see. But despite this coarse resolution, flies see and process fast movements very quickly.
We can infer how animals perceive fast movements from how quickly their photoreceptors can process light. Humans discern a maximum of approximately 60 discrete flashes of light per second. Any faster speed usually appears as a steady light. The ability to see faint flashes depends on the lighting conditions and the part of the retina you are using.
Mottled Lanterns are on the most wanted list: prepare to stomp

Some LED lights, for example, emit discrete flashes of light fast enough that they appear as a constant light to humans – unless you turn your head. In your peripheral vision, you may notice a flicker. This is because your peripheral vision processes light faster, but at a lower resolution, like the vision of flies.

Remarkably, some flies can see up to 250 flashes per secondabout four times more flashes per second than people can perceive.

If you took one of these flies to the cineplex, the smooth 24-frame-per-second movie you watched would appear, on the fly, as a series of static images, like a slideshow. But this quick vision allows it to react quickly to prey, obstacles, competitors and your attempts to crush.

Our research show it flies in dim light, losing some ability to see fast movements. This might seem like a good chance to crush them, but humans also lose their ability to see quick, sharp strokes in the dark. So you can be just as handicapped as your target.
When they fly in the dark, flies and mosquitoes fly erratically, with twisty flight paths to evade swats. They can also rely on non-visual cuessuch as information from small hairs on their bodies that detect changes in air currents as you move to strike.

neural stuff

But why do flies see more slowly in the dark? You may have noticed that your own vision becomes slow and blurry in the dark, and much less colorful. The process is similar for insects. Low light means fewer photonsand just like cameras and telescopes, eyes depend on photons to create images.
Rapid vision allows a fly to react quickly to prey, obstacles, competitors, and human attempts to crush.
But unlike a nice camera, which lets you upgrade to a bigger lens and collect more photons in dark environments, animals can’t swap the optics of their eyes. Instead, they rely on additiona neural strategy that sums inputs from neighboring pixels, or increases the time they sample photons, to form an image.
Larger pixels and longer exposures capture more photons, but at the cost of sharp images. Summing is equivalent to shooting with grainy film (higher ISO) or slow shutter speeds, which produce blurrier images, but avoid underexpose your subjects. flies, especially the little onescannot see quickly in the dark because, in a sense, they wait for enough photons to arrive until they are sure of what they are seeing.

Handling in flight

In addition to quickly perceiving imminent threats, flies must be able to take flight in a fraction of a second. This requires preparation for take-off and fast flight maneuvers. After visually detecting an imminent threat, fruit flies, for example, adjust their posture by a fifth of a second before taking off. Predatory flies, such as killer fliescoordinate their legs, wings, and halteres—dumbbell-like remnants of wings used to sense rotations in the air—to quickly grab prey in midair.

How to best swat a fly

To outsmart a fly, you must strike faster than it can detect your approaching hand. With practice you can get better, but flies have perfected their evasions over hundreds of millions of years. So, instead of swatting, it is better to use other means of managing flies, such as setting fly traps and cleaning backyards.

What makes mosquito bites itch and what to do about it

You can attract some flies to a narrow-necked bottle filled with apple cider vinegar and beer. Placing a funnel in the neck of the bottle allows them easy entry but difficult to escape.

When it comes to mosquitoes, some commercial repellents may work, but eliminating standing water around the house – in some plants, pots, or any open container – will help. eliminate their egg-laying sites and reduce the number of mosquitoes around from the start. Avoid insecticides, as they harm beneficial insects like bees and butterflies.
The conversation

Jamie Theobald is an associate professor of biological sciences at Florida International University. Ravindra Palavalli-Nettimi is a postdoctoral research associate at this university. Theobald receives funding from the National Science Foundation. Palavalli-Nettimi does not work for, consult, own stock or receive funding from any company or organization that would benefit from this article, and has not disclosed any relevant affiliation beyond a name university. Florida International University provides funding as a member of The Conversation US.

Leave a Comment