Game hunters have found strikingly “neon blue” meat inside wild California wild hogs, triggering advisories about potential contamination.
“I’m not talking about a little bit of blue,” Dan Burton, owner of a wildlife control company, told Salvador Hernandez at The Los Angeles Times.
“I’m talking about neon blue, blueberry blue.”
An investigation by local authorities found that the dramatic color change was caused by rodenticide poisoning, prompting them to issue a warning for the entire Monterey County area.
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Rat poisons containing the chemical compound diphacinone are often sold dyed blue for identification. Use of the compound has been heavily restricted in California since 2024.
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“Hunters should be aware that meat from game animals such as wild hog, deer, bear and geese could be contaminated if that game has been exposed to rodenticides,” says Pesticide Investigations Coordinator Ryan Bourbour of the California Department of Fish and Wildlife (CDFW).
“Rodenticide exposure may be a concern for non-target wildlife in areas where applications occur in close proximity to wildlife habitat.”
Worryingly, this is not the first time feral pigs in the region have had their entrails stained blue.
A popular agricultural rodent control, diphaquinone is a first-generation rodenticide that acts as an anticoagulant, causing severe internal bleeding.
It works by binding to an enzyme that recycles vitamin K. This reduces available vitamin K, making it impossible for animals’ livers to produce enough essential clotting factors to prevent internal bleeding.
Predators, including humans, that eat an animal poisoned with the toxin may become ill themselves; while the chemical breaks down faster than second-generation rodenticides, diphaquinone remains active in the tissues of the dead animal for some time, even if it is cooked.
Wildlife groups globally have long urged us to stop relying on chemical pesticides because of the collateral damage these poisons cause. From owls to bees, pesticides cause great harm to wildlife.
Non-target animals either consume it directly or are affected by secondary exposure when they eat other animals that have ingested the poison, adding further pressure to already endangered species.
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Difacinone has been found in the systems of many poisoned predators, including raptors, mountain lions, bobcats, foxes, as well as the endangered northern spotted owl and San Joaquin fox.
Although the prognosis is usually poor, anticoagulant poisoning can be treated in animals if it is caught before symptoms appear and vitamin K is given as an antidote.
But this devastating impact on wildlife is what has led to its strict control in California.
“Pesticide applicators are urged to take precautions when applying rodenticides to avoid exposing wildlife,” advises CDFW.
“Prior to application, it is important to ensure that non-target wildlife do not use the area where the pesticide is to be applied.
California feral hogs—which are hybrids between domestic pigs and European wild boars that were intentionally released a century ago—are voracious omnivores, so they would happily eat both poisoned rodents and bait.
Beginning in March of this year, a local hunter, Dan Burton, noticed several feral hogs going out of their way to obtain rodenticide-baited oats used in squirrel traps.
The associated dye appears to affect only the pigs’ fat, leaving the rest of their tissues colored normally.
Pesticides are also harmful to exposed humans. These have been linked to lower sperm count, diabetes, cancer, Alzheimer’s and other health conditions.
A recent US study found that the commonly used insecticide chlorpyrifos causes structural brain abnormalities and reduced motor function in children and adolescents.
Many of these pesticides have been used on a large scale without adequate long-term studies of their impact on human health.
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“Excessive and uncontrolled use of pesticides has led to food contamination as well as environmental, agricultural and aquatic pollution,” concludes a 2024 scientific review of pesticide use.
“To address the global threats posed by pesticides, international coordination and cooperation among nations is essential.”
Integrated pest management aims to mitigate the risks of such dangerous animal control practices by combining several safer strategies. These include encouraging natural predators and building fences, traps and other barriers such as vents.
Other animal deterrents may include the targeted use of light and sound, such as playing talkback radio, or the application of fragrances such as peppermint essential oil.
CDFW urges anyone who encounters blue animals or other abnormalities to report them to the Wildlife Health Laboratory; the details are here.
An earlier version of this article was published in August 2025.