In 1997, NASA sent 64 desert beetles to Russia’s Mir space station with tiny wheels tracking their every movement; their movements helped scientists understand how light regulates biological clocks in microgravity

In May 1997, NASA sent 64 black desert beetles into space aboard the Space Shuttle Atlantis as part of the STS-84 mission. The shuttle docked with the Russian Mir space station, where the beetles were kept in individual chambers equipped with tiny wheels that turned whenever they moved.

The insects spent about 125 days aboard Mir before returning to Earth on a later shuttle mission in September 1997. During that time, scientists on Earth monitored the revolutions of the miniature wheels to study how the beetles’ activity changed in microgravity.

The experiment produced insights into how living organisms keep time. Researchers found that pulses of light could shift the beetles’ internal clocks even in near-weightlessness, while changes in gravity affected their natural rhythms in a different way.


The seemingly unusual experiment was aimed at understanding a serious challenge for human spaceflight: maintaining healthy sleep and circadian rhythms during long missions. Without the regular sunrise and sunset experienced on Earth, astronauts can lose important environmental cues that help regulate their biological clocks.

Tiny wheels tracked every movement

The species used in the experiment was Trigonoscelis gigas, a desert beetle collected from the Turkmenian sand desert.

The species’ adaptation to extremely dry conditions and its well-defined circadian rhythm made it useful for studying biological clocks under altered environmental conditions.

Each beetle was housed separately inside a device known as a Beetle Activity Monitor. The enclosure contained a small wheel that rotated as the insect walked, allowing researchers to continuously record its activity.

The spacecraft carried two kits containing 32 beetles each, for a total of 64 insects. Once aboard Mir, the kits were placed in the Priroda module.

Researchers could independently control the lighting conditions in the different kits. This allowed them to expose groups of beetles to different light schedules while all of the insects experienced the same microgravity environment.

What the spinning wheels revealed

The experiment examined two aspects of the beetles’ biological clocks.

One part investigated whether a brief pulse of light could shift the insects’ circadian rhythm depending on when the light was applied. Another examined how the intensity of light affected the length of the beetles’ natural activity cycle.

The results showed that a light pulse could shift the beetles’ internal clocks forward or backward depending on when it was delivered. This indicated that the light-sensitive mechanisms involved in regulating their circadian rhythm continued to function in microgravity.

Researchers also found that gravity influenced the beetles’ natural rhythm. Studies comparing microgravity, normal Earth gravity and centrifuge-generated hypergravity showed changes in the insects’ free-running period, or the length of their natural biological cycle in the absence of normal environmental timing cues.

The findings indicated that light and gravity affected the circadian system through different mechanisms rather than producing identical effects.

Beetles had separate activity peaks

The insects displayed a characteristic daily activity pattern, with two major peaks occurring around dawn and dusk.

Earlier research suggested that these peaks could be controlled by separate oscillators — biological timing systems that operate within the circadian system.

The fact that the two activity peaks could respond differently to changes in gravity provided evidence that the beetles’ sense of time was not necessarily controlled by a single, simple biological clock.

Instead, their circadian system appeared to involve multiple timing mechanisms that could respond differently to environmental signals such as light and gravity.

Why NASA studied beetle body clocks in space

Although the experiment involved insects, its broader purpose was connected to human spaceflight.

On Earth, the human circadian rhythm is strongly influenced by the natural cycle of daylight and darkness. In orbit, astronauts do not experience the same regular sunrise and sunset pattern, while microgravity removes another environmental condition that organisms evolved with.

Understanding how biological clocks respond when these signals change can help scientists study the mechanisms behind sleep, alertness and daily activity during space missions.

The 1997 beetle experiment therefore provided researchers with a way to isolate the effects of light and gravity on a relatively simple biological system.

More than two decades later, the mission remains part of the history of space-based circadian research. The 64 beetles are long gone from orbit, but the tiny wheels that recorded their movements helped scientists investigate a fundamental question: how does a living organism keep track of time when the environment it evolved in has been completely changed?