For any organism to exist outside of Earth’s protective atmosphere, it must overcome a severe combination of physical extremes. The conditions of space—a near-perfect vacuum, intense radiation, and wild temperature swings—challenge every fundamental aspect of terrestrial life. Exploring the survival of spiders requires differentiating between two scenarios: life inside a controlled spacecraft and exposure to the absolute vacuum of outer space. The answer shifts dramatically depending on the specific environmental context.
Spiders in Protected Space Environments
Spiders have successfully flown and lived aboard spacecraft, providing a direct answer to part of the survival question. These arachnids were first sent into orbit in 1973 aboard the Skylab 3 mission, which carried two European garden spiders (Araneus diadematus). More recently, golden silk orb-weavers (Trichonephila clavipes) were observed on the International Space Station (ISS) in 2011 as part of student-led experiments. These missions demonstrated that spiders can survive and function in the microgravity environment of orbit.
Their survival was entirely dependent on the pressurized, temperature-controlled, and life-supporting habitats provided by the crewed spacecraft. The spiders were kept in sealed enclosures that replicated Earth-like atmospheric conditions, including a breathable mix of gasses and a stable temperature range. The success of these experiments confirms that spiders can endure the launch process and the long-term effects of weightlessness, as long as a miniature Earth environment is maintained.
Physiological Limits in the Vacuum of Space
Unprotected exposure to the true vacuum of space would result in an instantaneous and lethal failure of the spider’s biological systems. The most immediate threat is the lack of ambient pressure, not freezing or radiation. All body fluids, including the spider’s hemolymph, would begin to boil at normal body temperatures in a process known as ebullism. This occurs because the boiling point of water drops significantly when the external pressure is extremely low.
Spiders rely on specialized respiratory organs called book lungs, which are stacks of alternating air pockets and hemolymph-filled tissue. Gas exchange in these organs occurs by passive diffusion. In a vacuum, there is no external air pressure to drive the necessary gas exchange, leading to immediate asphyxiation. The rapid loss of moisture due to evaporation and sublimation from the body surface would also quickly cause fatal dehydration. The combination of immediate asphyxiation and ebullism means an unprotected spider would die within seconds of exposure.
The Challenge of Microgravity and Web-Building
Observations from the space missions concerned how spiders adapted their behavior to the absence of gravity. On Earth, orb-weaving spiders use gravity as their primary orientation cue, resulting in asymmetrical webs with the central hub closer to the top. The spider waits on the hub facing downwards, allowing gravity to assist its movement toward trapped prey. In the microgravity of the ISS, this innate behavioral pattern was initially disrupted, and the spiders spun erratic or incomplete webs.
After an adjustment period, the arachnids began to construct webs that were noticeably more symmetrical, with the hub positioned closer to the geometric center. Researchers discovered that the spiders began using an alternative sensory cue for orientation. When the habitat lights were on, the spiders used the light source as a substitute for “up,” leading them to build webs that were once again asymmetrical, with the hub near the light. This demonstrated sensory compensation, where the visual cue of light replaced the physical sensation of gravity to guide their complex construction behavior.