No, there are not living animals crawling on Mars. The images show dark, branching surface marks on the red planet, and scientists call them mars spiders because their shape looks spider-like from orbit.
These features are real, but they are geological patterns made by ice and gas, not actual creatures.
You usually find these patterns in the polar region of Mars. Seasonal CO2 ice builds up during winter and changes in spring.
The result can look eerie in spacecraft photos. That is why the nickname has stuck.
The “spiders” are part of araneiform terrain, a name that refers to spider-like channels and pits carved into the ground. This is a surface process shaped by cold seasons, not biology.
From above, the features have a body-like center with branching lines that spread outward like legs. Orbiters capture them in a way that makes them look unusual, even though they are just patterns in ice and dust.
Araneiform terrain forms in areas where frozen carbon dioxide changes with the seasons. The term helps scientists describe the shape without suggesting anything alive is there.
The process starts with winter ice and ends with spring gas release. That seasonal cycle can crack the surface, move dust around, and leave behind the dark, spidery marks you see in images.
During winter, carbon dioxide ice forms a dry ice layer over the ground. When spring sunlight returns, the ice at the bottom starts to turn directly into gas, a process called sublimation.
As the gas builds under the ice, pressure rises until it breaks through. Dust gets carried upward in jets, and the falling material leaves dark spots and branch-like channels on the surface, as described by ESA’s Mars Express report.
This is not a common Earth-like pattern because it depends on a very thin, seasonal layer of dry ice and a cold Martian climate. The result can stretch from tiny marks to features that span hundreds of meters.
You can spot these features most clearly near the southern polar terrain, especially around complex landscapes like Angustus Labyrinthus. Mars orbiters have shown both the dark spots on the surface and the web-like channels below.
Angustus Labyrinthus is also known as Inca City, a region first found by Mariner 9. ESA notes that many of the dark spots appear near this area, where rough hills and plateaus make the terrain easy to study.
Mars Express used its High Resolution Stereo Camera to capture the dark surface spots linked to the gas bursts. The image showed the marks scattered across hills and plateaus, which helped confirm how widespread the features are.
The ExoMars Trace Gas Orbiter has captured the tendril-like patterns even more clearly. In the ESA image set, the orbiter showed the branching channels that sit below the darker surface marks, adding a clearer view of the full shape.
Lab work has reproduced the process on Earth. This gives you strong evidence for the ice-and-gas explanation.
Some questions remain about why certain regions grow these patterns more easily than others.
Researchers used a dirty under-vacuum simulation testbed for icy environments and a liquid-nitrogen-cooled test chamber to mimic Martian conditions. These tests showed how gas escaping through ice can carve spider-like shapes, a result also discussed in a Planetary Science Journal study on Mars terrain experiments.
The features seem to need the right mix of ice thickness, sunlight, and surface material. Areas with layered frost and loose dust may be better at producing the dark branching patterns than smoother ground.
What Remains Uncertain About Their Growth
Scientists still debate details like how the channels widen over time. Researchers also question why some sites make large clusters while others do not.
The main process is clear. Scientists continue to study the fine steps of growth.
