Little inspires human ingenuity, or overcomes moral scruples, like the desire for improved means of smiting one’s enemies. From sharper swords to bigger bombs, soldiers have always sought an edge. And long before either swords or explosives existed, scholars believe, Paleolithic warriors were hurling “bee bombs”—nests of stinging insects—into enemy caves. That was 100,000 years ago, notes Jeffrey Lockwood, entomologist and author of Six-Legged Soldiers (Oxford UP), and it marked, of course, only the beginning. By the end of the Second World War, the Nazis had 30 million Colorado potato beetles ready to unleash on British crops, and Japan’s Unit 731 had killed more people in China with infected fleas and flies than atomic bombs had killed in Japan.
Less well known than bacteriological warfare, with which it is intimately linked—nothing delivers epidemic disease like an insect host—war by bug has left its mark on the historical record. Roman engineers liked to toss entire beehives into besieged cities, and defenders too deployed insects, along with boiling oil and large rocks. On their south-facing sides, some medieval castles had bee boles, warm recesses attractive to hive builders, which ensured there would always be a ready source of six-legged defenders.
Before the 20th century, however, insect conscripts never caused a fraction of the mortality that freelance bugs did. In the American Civil War, in which some 620,000 soldiers died, two-thirds were felled by disease, most of it spread by insects. After scientists established the insect-disease role in epidemics, everything changed. The Japanese were the first to grasp the military implications. In the Russo-Japanese war of 1904 the Imperial army became the first in history to lose fewer men to sickness than to weapons.
But the possibilities of knowledge always cut both ways with humans. It was the very strength of Japanese medical science—galvanized by a ruthless microbiologist named Shiro Ishii—that later unleashed the most horrific insect-fought war ever. Ishii set up shop in the puppet state of Manchuria to test his biowarfare theories on human guinea pigs. His Unit 731 grew to have a budget rivalling that of the Manhattan Project, and a staff of 10,000. At first, despite barbarous procedures—infected prisoners were vivisected so precise records of the disease’s effects could be kept—Unit 731 was unable to kill people in sufficient numbers to impress the high command. Fragile pathogens tended to die off before initiating epidemics.
Then Ishii had his conceptual breakthrough: insects, he realized, not only delivered diseases, they protected them en route. So Ishii devised a Dante-esque perpetual plague machine. A four-storey granary was built to attract, feed and house a rat colony. Rats were captured, infected with plague, and held immobile. Fleas were dumped from test tubes onto the rats’ shaved stomachs. Once infected, they were harvested by semi-nude workers, whose bare skin gave them a chance to detect and brush off escaped fleas before they could bite. Infected fleas were then placed in incubators with uninfected rats and fleas. In this way Ishii ramped up monthly production to an astonishing 15 kg of plague fleas, 45 million individual fleas.
It worked so well for Ishii—bombers dropped flea canisters on Chinese villages, sparking plague outbreaks that continued erupting into the 1950s—that he sought, and found, a related method to deliver something even more lethal. In May 1942, Japanese bombers attacked the city of Baoshan with standard explosives and a few ceramic shells, known to Unit 731 as “maggot bombs.” They burst open on impact, disgorging their contents—houseflies in a slurry of cholera bacteria. The bombers came back three times that week, for the sole purpose of driving the sick into the countryside. The explosive bombs killed 10,000 in Baoshan, but the regional cholera epidemic took 200,000 lives.
In all, Japanese biological warfare killed 580,000 Chinese, most by insect. There were war crimes trials in Tokyo after the war, as there were in Nuremberg, but Ishii and his men never appeared in court. He retired on a full military pension, while some of his staff rose to high positions—between 1947 and 1983, every head of the Japanese National Institute of Health, with one exception, had served in Unit 731. Why such leniency? The Americans, focused on a possible war with the Soviets—and seeking an edge—had cut a deal with Ishii in return for his research.