06/16/2026
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A California ground squirrel chews up shed rattlesnake skin, licks the scent into its fur, heats its tail by pumping blood from its core, and waves the superheated tail at the rattlesnake in a frequency the snake can see in infrared but the squirrel cannot see at all.
It does this only against rattlesnakes. When it encounters a gopher snake, which cannot detect infrared, it waves the tail cold. The squirrel knows which snake can see heat and adjusts the signal accordingly. Researchers at UC Davis had to build a robotic squirrel to prove it.
Ground squirrels make up roughly seventy percent of the northern Pacific rattlesnake's diet. That number means this is not an occasional encounter. It is the central relationship in both animals' lives. The rattlesnake eats ground squirrels more than it eats anything else. The ground squirrel is hunted by rattlesnakes more than by any other predator. The two species have been locked in an arms race on the same California hillsides for so long that the squirrel has evolved a defensive package that reads like it was designed by a military contractor.
The scent application was documented by Barbara Clucas, a graduate student in Donald Owings' animal behavior lab at UC Davis, and published in the Proceedings of the Royal Society B in 2008. Clucas observed California ground squirrels and rock squirrels picking up pieces of shed rattlesnake skin, chewing them, and licking the paste into their own fur.
They also collected snake scent from soil and rocks where rattlesnakes had been resting. Adult females and juveniles applied snake scent more frequently than adult males. The reason is survival math. Adult male ground squirrels are large enough to survive a rattlesnake bite. Adult females are smaller. Juveniles have not yet developed enough venom-resistance protein to survive one. The animals most vulnerable to being killed by a rattlesnake are the ones wearing rattlesnake perfume.
The scent probably works in two ways. A rattlesnake approaching a burrow at night smells snake instead of squirrel and may bypass the entrance entirely. A rattlesnake that enters the burrow may hesitate if the scent suggests another snake is already inside. Mothers lick their pups to transfer the scent, coating the young in a chemical disguise before they are old enough to apply it themselves.
The infrared tail signal was discovered by Aaron Rundus in Owings' lab and published in PNAS in 2007. Rundus filmed ground squirrels confronting live rattlesnakes in a controlled lab environment using an infrared camera. When a squirrel faced a rattlesnake, it raised its tail, flagged it back and forth, and simultaneously dilated the blood vessels in the tail, flooding it with warm blood from the body core.
The tail temperature rose several degrees, matching the heat of the rest of the animal. In the rattlesnake's infrared vision, the squirrel suddenly appeared much larger. A small rodent waving a cold tail is a meal. The same rodent waving a tail that glows hot in infrared is something harder to assess, and the hesitation costs the snake its ambush.
Rundus tested the mechanism with a robotic squirrel that could flag its tail with or without infrared heating. When the robot flagged with heat against live rattlesnakes, the snakes were significantly less likely to strike. When the robot flagged cold, the deterrent effect dropped. The squirrel's defense is not just visual. It is broadcasting on a channel that only pit vipers can receive.
The squirrels also assess individual snakes. Research from Owings' lab showed that ground squirrels can evaluate how dangerous a specific rattlesnake is by the sound of its rattle. They adjust their approach based on the assessment. Against a less dangerous snake, they mob aggressively, kicking sand, bobbing their heads, and advancing. Against a more dangerous snake, they increase their distance and rely more on the tail signal. They are reading the threat in real time and calibrating the response.
Naturalists in the 1940s first noticed California ground squirrels walking directly up to rattlesnakes, waving their tails, and kicking dirt. They had no explanation for why a prey animal that constituted seventy percent of the snake's diet would approach its primary predator on purpose.
Eighty years of research later, the explanation is that the squirrel is not approaching its predator. It is deploying a layered defense system that includes chemical camouflage stolen from the enemy's own skin, an infrared broadcast tuned to the enemy's most sensitive receptor, venom resistance that makes a bite survivable for adults, and a behavioral assessment protocol that reads the individual threat level of each snake it encounters. The rattlesnake has heat vision, venom, and an ambush strategy refined over millions of years.
The ground squirrel stole the snake's scent, cracked the snake's infrared channel, neutralized the venom, and kicks sand in its face while doing it.
Source: Clucas et al. (2008), Proceedings of the Royal Society B. Rundus et al. (2007), PNAS. Donald Owings and Richard Coss labs, UC Davis. National Geographic, 2007. CapRadio, October 2025.
