In 1990, the USSR sent six Japanese tree frogs to the Mir space station for an eight-day experiment, where researchers watched them float with all four legs stretched out and their bodies bent backward - then found the frogs improved their ability to land after jumping in microgravity

Six Japanese tree frogs in December 1990 were sent aboard the Soviet space station Mir as part of an experiment designed to see how their bodies and movements responded to microgravity. The frogs traveled to orbit with the crew and remained there for eight days, while researchers observed their posture, movement, feeding responses and ability to orient themselves without normal gravity.

The findings were later reported in a 1991 paper, “Behavior of Japanese Tree Frog under Microgravity,” led by Akemi Izumi-Kurotani and published in Biological Sciences in Space. Toyohiro Akiyama, the TBS journalist who became the first Japanese person in space, was among the paper’s authors.

The flight that carried the frogs to Mir

On December 2, 1990, the frogs began their journey to orbit aboard Soyuz TM-11, launched with Japanese journalist Toyohiro Akiyama and Soviet cosmonauts Viktor Afanasyev and Musa Manarov. The spacecraft reached the Mir space station two days later. The frogs were carried in a specially designed Life Support Box and later released into a glove bag on the station, where their movements and responses to various stimuli could be observed and recorded.

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What happened to the frogs in microgravity

Once released inside Mir, the frogs displayed a distinctive posture when floating. They stretched all four legs outward, bent their bodies backward and expanded their abdomens, resembling the posture they had shown during brief periods of weightlessness in earlier experiments.

The researchers also noticed an unusual behavior among frogs resting on surfaces. Four of the six frogs observed in the experiment bent their necks backward to a greater extent than had been seen on Earth. They also tended to walk backward while maintaining this position.

The frogs could still respond to external stimuli. When a leg touched an object while they were floating, they attempted to pull themselves toward it. They also showed responses to moving objects and mealworms, although one frog attempting to catch a mealworm was unable to eat it in the microgravity environment.

The experiment produced a clue about adaptation

The most revealing result came when the researchers repeated some observations. During the second experiment, the frogs became better at landing or perching on surfaces after jumping.

The number of failed landings fell from an average of 2.7 during the first experiment to 1.4 during the second, suggesting that the animals were beginning to adapt their movements to the unfamiliar microgravity environment.

The experiment also produced an important result after the frogs returned to Earth. All six survived the eight-day mission. Initially, their movements were slower, and some aspects of their vestibular function appeared impaired, but their behavior and vestibular responses returned to normal within about 2.5 hours of landing.

From a space experiment to a scientific record

The observations gave researchers a rare look at how an amphibian adapted its posture and movement when gravity was largely removed. A later paper by the same research team, published in Advances in Space Research in 1994, again examined the Mir observations and reported that the frogs' ability to land after jumping improved during the mission, while their normal behavior returned relatively quickly upon returning to Earth.