Understanding upside-down landings of flies

Turning around and settling on the ceiling involves four steps

November 16, 2019 07:32 pm | Updated 07:33 pm IST

Complex task:  The data indicates that ceiling landings may be more ‘difficult’ for a fly.

Complex task: The data indicates that ceiling landings may be more ‘difficult’ for a fly.

“When I was a student, Late Prof. K. S. Krishnan who was on the interview panel asked me, ‘how do flies land on the ceiling?’ Although seemingly an innocuous question, it turns out to be a really complex phenomenon,” says Prof Sanjay Sane from the National Centre for Biological Sciences, Bengaluru. Now, after several years of research using the modern state of the art tools and months of video recordings his team has answered the question. The paper recently published in Science Advances notes that the inverted landing “involves a serial sequence of well-coordinated behavioural modules.”

Four steps

The international team lists out four steps that take place in the complex process which includes upward acceleration towards the ceiling and then based on visual inputs it begins to rotate - pitch and roll. It then flings all six legs and prepares to land, and in the final stage does a leg-assisted body swing and lands firmly.

Precision landing

The question is how is it possible to do all the four steps so precisely. It involves visual, neurobiological and gyroscopic inputs. The team used video recordings of how blue bottle flies land and by plotting the distance at which landing is initiated and speed at that point, they concluded that they have to initiate deceleration at 40 microseconds speed. For easy comparison, we blink our eyes at about 150 to 200 microseconds. If the fly missed initiating the landing response within this window, it ended up colliding with the substrate.

The team from NCBS had previously compared how houseflies land on the straight wall and inverted ceiling. The results published earlier this year in PLOS ONE noted that in both cases, the fly uses the same landing manoeuvres but there are also notable differences in both types of landing.

Difficult task

“To orient itself in an inverted position, a fly can either perform a roll rotation or a pitch rotation or a combination of both,” explains Sujay Acharya, the first author of the paper from NCBS in an email to The Hindu.

“Vertical landings on the other hand are highly stereotyped. As the fly approaches the wall, it pitches up before contact. Our data also indicates that ceiling landings may be more ‘difficult’ for a fly. We observed that in close to half the cases, a fly landing on a ceiling bumped into it. Whereas, we did not observe such collisions for vertical landings.”

Prof. Sane adds that, “This study will help us gain insights into how the nervous system acquires and integrates inputs from multiple sensory modalities to execute a fast but precise behaviour.” He also explains that these flies belong to the Dipteran order which means they have only one pair of wings and their hind wings are modified into special structures called halteres, which helps in body orientation and alerts them when they are involuntarily pitching or rolling.

Inspired by nature

“We look at nature for inspiration. This helps drive the fundamental science of engineering, to understand how flies are able to solve these problems so we can apply them to future technologies,” explains Prof. Jean-Michel Mongeau, one of the authors from Pennsylvania State University in a release. “This work reiterates how fast these [manoeuvres] are executed within an extremely small nervous system. This data can lead to new hypotheses for understanding how brains function.”

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