A wildlife trapper in Monterey County made an unexpected discovery after capturing a series of wild pigs in March of this year. While processing the animals, the trapper found several with blue-tinged muscles and fat tissues. The bizarre discoloration is a result of exposure to diphacinone, an anticoagulant rodenticide that is often dyed to identify it as a poison, according to the California Department of Fish and Wildlife.

In an email to SFGATE, Fish and Wildlife pesticide investigations coordinator Ryan Bourbour said that the trapper observed the wild pigs eating directly from rodenticide bait stations. The scope of the contamination appears extensive across the southern part of Monterey County and along the Salinas River, according to KSBW-TV.

Wild pigs are adaptable hybrid creatures. Part domesticated pig, part wild boar, they can weigh upward of 200 pounds and now live in 56 out of 58 counties across the state. SFGATE previously reported on their increasingly aggressive behavior, including charging at a hiker. 

Vince Bruzzone, owner of Full Boar Trapping & Wildlife Control, is familiar with the oddity. “I have heard of this happening in agricultural ‘heavy’ areas like Salinas and other parts of the Central Coast,” he told SFGATE in an email. Bruzzone’s company was recently contracted by the Santa Clara Open Space Authority to help manage its wild pig population over the next three years for $243,000. He said he takes proactive measures because of this contamination issue. “I do make a point to tell those I donate carcasses to that if they ever were to come across blue meat from one of my pigs to dispose of it at a landfill (rather than dumping it) and bring me the bill so that it doesn't enter the food chain,” he said.

The situation reveals a paradox: While California banned diphacinone for most uses in January 2024, agricultural operations have exemptions due to their pest control needs. That loophole has broad ecologic implications. A 2018 statewide study found rodenticide residues in 8.3% of wild pig tissue samples — and in an alarming 83% of bear samples — mainly in animals frequenting agricultural zones. Wildlife officials warn that this contamination can ripple through the food chain, since wildlife can be inadvertently consuming poisoned prey.

After confirming the presence of diphacinone in the liver and stomach contents of wild pigs with blue tissues, Fish and Wildlife’s Wildlife Health Laboratory is advising hunters to not consume meat from any animals showing discoloration. Visible signs aren’t always reliable, however. “As demonstrated by findings of exposure in nongame animals, the discoloration is not always present and is not a reliable indicator of AR [anticoagulant rodenticide] residues in meat,” the 2018 study said.