They say that rain is a blessing. Showering the Earth and making the grasses look a bit greener— but what if it is an ooey-gooey, deadly, yellow rain?

The Deadly Drizzle

It was one bright and sunny day in 1981 when the Vietnamese and Laotian people noticed a sticky yellow liquid occasionally pouring down on them from the skies. According to witnesses, the strange yellow rain killed plants and gave people headaches, seizures, even blindness. The Vietnam war just ended a few years back, so the people are still untrusting.

The Hmong people, who fought alongside France against the Southeast Asian communists, were greatly affected. It was reported that the frequency of the “chemical attacks” increased in 1978-1979, reaching 260 incidents. Claims said that these attacks followed a pattern: usually, a slow-flying plane would drop bombs that explode slightly above tree level on sunny afternoons. They would then disperse colored smoke or oily liquid. Some say they were red, green, white, pink, yellow, and blue. Are they being bombarded with different toxic chemicals?

According to the then-United States Secretary of State Alexander Haig, the answer was yes.


After a lengthy, six-year investigation, Haig(A former General and NATO Commander)accused the Soviet Union of being the culprit behind what was tagged as the “yellow rain.” He said, “the international community has been alarmed by continuing reports that the Soviet Union and its allies have been using lethal chemical weapons in Laos, Kampuchea, and Afghanistan” and that they have found physical evidence that was analyzed and found high levels of T-2 mycotoxins. The Soviet Union, of course, denied this accusation.  Of course, we all know that T-2 mycotoxins are a mold that comes from the toxic fungus Fusarium-ssp.

(We all know that right?)

People were left perturbed when a mysterious yellow substance suddenly fell from the sky in Southeast Asia. Photo from WNYC Studios, Radiolab.

Matt Meselon, a Harvard University biologist, was skeptical of the US analysts’ claim, so his team had a closer look. After their investigation, they found out that the testimonies of the witnesses were inconsistent. For instance, the yellow substance would still pour down even when there weren’t planes insight (assuming these “bioweapons” were dropped by the Soviet Union from their aircraft.) Also, when the Yellow Rain dried, it turned to yellow dust. When checked under a microscope, it turned out to be pollens.

He had a theory: bee poop.

But why would thousands and thousands of bees decide to poop at the same time in the same area? Canadian biologists and Malaysian scientists were able to answer the question in 1989. The warm days caused the bees to leave together in a swarm, defecate, then come back to care for their larvae. They confirmed this by measuring hundreds of bees’ body mass before leaving their hives. After returning, they discovered the bees were 20% of their weight. It turned out, Asian honey bee larvae are sensitive and get deformed from high temperatures, so the adult bees had to reduce their mass (by pooping) to prevent them from overheating inside the hives.

Unidentified bee (Megachile sp.) collecting pollen, Taman Sari, Yogyakarta 2014-05-19. ©Chris Woodrich, Crisco 1492, CC BY-SA 3.0, via Wikimedia Commons

Next question, why did nobody see the bees? They flew at around 50 feet altitude with a speed of approximately 20 miles per hour, which was difficult to see.

Despite all these proofs, the US government did not retract its allegation against the Soviet Union.


So, Yellow Rain was nothing other than bees trying to shed some poop-weight to stay cool in the hive, which unfortunately occurred just after the Vietnam War when people were still a bit jittery and worried about being attacked. Recently Vietnam had fought a brief war with Communist China over their competing interests in Cambodia which only added to the paranoia.  As for the U.S. blaming the Soviets, chalk that one up to just another propaganda skirmish of the Cold War.