1981: Alexander Haig announced that the United States was in possession of “physical evidence” that the Soviet Union was supplying its Southeast Asian allies with biological warfare agents for military use against their opponents. According to the Secretary of State, the Soviet Union was providing Laos and Vietnam with mycotoxins – poisonous compounds synthesized by fungi.
The “physical evidence”? Hmong villagers, refugees from fighting in Laos, had seen low-flying aircraft spraying what the Hmong called “yellow rain”, an oily liquid that left a residue of yellow spots on leaves, rocks and rooftops. Villagers caught in these chemical showers exhibited symptoms that included blurred vision, breathing difficulties and skin burns. Between 10 and 20 per cent of victims died.
If Haig was correct, the Soviet Union had violated international accords covering chemical and biological weapons. It was a dramatic and serious allegation.
On closer scrutiny, however, the “eye-witness” accounts of the refugees were found to be second- or third-hand reports, the medical evidence was questionable and analysis of the yellow spots showed that they consisted mainly of pollen.
The “yellow rain” almost certainly resulted from the mass release of digested pollen grains by swarms of bees. In other words, Haig’s toxic agents were in fact bee droppings. Hmong housewives didn’t want them spattered all over their nice clean laundry, but they were harmless.
Source: The Nonproliferation Review, Spring 2001