They are slimy, squishy, and slow-moving creatures with long bodies with no legs, pretty much like homeless snails. Slugs are land-dwelling mollusks that are considered garden pests: Hiding during the day but crawling out at night to slide across your garden pathway and onto the leaves, chewing off your beloved daffodils before retreating and leaving behind their unmistakable trail of silvery mucous. It’s safe to say that many of us are not fans of slugs. However, during World War I, these mollusks actually played a totally different role when they became some sort of life-saving, organically-powered, costless life-savers.

Gas Uses During WWI

World War I was an era of gas warfare. When the Germans first used the deadly chemical weapon in 1917, the troops were basically unprepared for the kind of attack. They had trouble detecting whether or not an area was contaminated. During World War I, the production of different dangerous chemicals started.

Tear gas was among the first gasses used. The chemical causes irritation, coughing, and burning sensations in the eyes, mouths, and nose, thus making you tear up. It was not lethal enough to kill people, so chlorine gas followed. Chlorine was deadly and could damage the tissues of the eyes, throat, and lungs after contact. The chemical could cause fluid to form in the lungs and basically drown people from the inside. The disadvantage of using chlorine gas was that it has a yellow-green color that screams its grand entrance, so the victims could immediately tell if they were being attacked.

There was also phosgene gas, which as opposed to chlorine, was colorless. The French first used the highly toxic chemical in 1915, which could also cause the lungs to fill with a liquid called pulmonary edema. Around 85,000 soldiers fell victim to this chemical. Then there was mustard gas that could soak up the troops’ clothes and cause severe blistering upon skin contact. Mustard gas is not easy to detect either until the victims start to itch and then, later on, develop large blisters.

The major problem was that the military didn’t have sophisticated technology back then to enable them to create masks like the M50 Joint Service General Protective Mask or MOPP gears. They even thought soaking masks with urine would offer some protection from the harmful effects of these chemical gases, you still had a face soaked in your own urine. Hopefully, it was your own.

Although less than 1% of the total deaths in the war were from gas, the fear instilled in the troops was huge. After World War I, the Geneva Protocol of 1925 prohibited the use of chemical warfare.

Slugs as Mustard Gas Detectors

The use of slugs as mustard gas detectors started with a curator named Paul Bartsch at the Smithsonian’s US National Museum, now called the National Museum of Natural History. His discovery was purely accidental as he brought these slugs home one day, and they escaped from their enclosure and crawled into his furnace room. When Bartsch found the slugs, they looked so distressed: the slugs were doing some weird movements with their tentacles to show that they were distressed.

He didn’t really think much of it until a few years later, the United States entered World War I in 1917, and he recalled the reaction of the slugs in his furnace room and thought they could possibly be useful. He went back, collected some slugs, and conducted experiments to see if the mollusks would react to the mustard gas. He found out that they were extremely sensitive, more than humans and more than other animals that were commonly used to detect gases like dogs. He informed the US Army about it, and the army entertained the idea.

Enlisting in the Army

As it turned out, slugs react at levels of one particle per 10-12 million and would compress their bodies and close off their breathing spores to survive the gas attacks or whatever chemicals without a fuss. Compared to horses and dogs with fatal responses, the slugs don’t incur adverse effects.