The tide may finally be turning in favour of the humans in our war on rats, Jordan Kisner writes for The Guardian. Trying to kill rats is futile: under pressure they multiply faster. “The rat’s primary survival skill, as a species, is its unnerving rate of reproduction. Female rats ovulate every four days, copulate dozens of times a day and remain fertile until they die… This is how you go from two to 15,000 in a single year. When poison or traps thin out a population, they mate faster until their numbers regenerate.” The solution is to keep them from mating, which would collapse rat colonies without rebound — essentially putting rats on the pill — but “until recently no pharmaceutical product existed that could make rats infertile, and even if it had, there was still the question of how it could be administered.” An Arizona company, SenesTech, claims to have found the solution in a liquid product that, in tests, caused a drop in rat populations of roughly 40% in 12 weeks. “This will change the world,” Loretta Mayer, a biologist and CEO of SensTech, says. The trick for the company was to make the liquid potable for rats, which are known to avoid what they don’t know. City rats, in particularly, will be difficult because they’re simply so well-fed. Another problem was that the liquid’s “active ingredient, 4-vinylcyclohexene diepoxide (VCD), is bitter and caustic” and rats “have the same taste preferences as humans”: they prefer fat and sugar. “ContraPest, the finished product, is viscous and sweet” and it did not kill the rodents. Kisner describes the development of ContraPest and SenesTech’s CEO and investors as something that “sounds crazy: a band of animal lovers and firemen in the mountains of Arizona, led by a Buddhist girl scout, making a pink milkshake for rats that may eventually improve the lives of [mns] of people.”

Rats aren’t entirely bad, though, according to some misguided souls. They are being used in a wide range of fields — from detecting landmines to testing for diseases. One tech startup named Apopo is even using African giant pouched rats to detect tuberculosis in humans. The rats, affectionately named HeroRats, have a significantly higher correct diagnosis rate than conventional tests at just a fraction of the cost, Ashoka Ireland’s communication manager Fiona Koch writes for Silicon Republic.

The Calhoun experiments on mice, rats, crowding and density — the real life inspiration for The Secret of NIMH: Some of our readers may be familiar with the 1971 children’s book Mrs. Frisby and the Rats of NIMH, later adapted into the 1982 animated film The Secret of NIMH, featuring this now-famous scene with the Great Owl (2:48) which served as nightmare fuel for an entire generation. The book and film tell the story of a widowed mouse trying to save her home from a farmer’s plow by seeking the help of rats who had been experimented on and had achieved literacy and technology. What is less well known is that the book and film were inspired by a series of experiments on mice and rats beginning in 1968 at the Bethesda, Maryland National Institute of Mental Health (NIMH). As detailed two weeks ago by Atlas Obscura’s Cara Giaimo in ‘The doomed mouse utopia that inspired the ‘Rats of NIMH,’’ Dr. John Calhoun set out to study the effect of raising mice in controlled settings where the only constraint on the growth of their population was the setting of their communal nest. “They were given the run of the place, which had everything they might need: food, water, climate control, hundreds of nesting boxes to choose from, and a lush floor of shredded paper and ground corn cob.”

While the work was ongoing, many tried linking the results of Calhoun’s findings to rising population sizes and densities of humans living in urban settings. “There could be no escape from the behavioral consequences of rising population density,” according to Calhoun in one of his early papers. In each experiment, the population of the mice would double before suddenly crashing into a terminal decline as the majority of the specimens exhibited pathological behavior resulting from the frequency of the unwanted social interactions. As noted in a report by the World Health Organization on the Calhoun experiments: “It seemed that the adrenal system offered the standard binary solution: fight or flight. But in the sealed enclosure, flight was impossible. Violence quickly spiralled out of control. Cannibalism and infanticide followed… Calhoun called this vortex ‘a behavioural sink,’… At the experiments’ end, the only animals still alive had survived at an immense psychological cost.”

But was the problem density, or crowding? Residents of megalopolises such as Cairo may hear of such reports and wonder how the findings of Calhoun’s experiments may ultimately play out with regard to human populations. However, follow-up experiments on humans found no ill-effects on greater density. Rather, as the WHO report notes, “focus now shifted away from simply identifying the pathological consequences of density and towards factors that mediated its effects. This was aided by a distinction between ‘density’ as a physical measure and ‘crowding’ as a subjective response… Researchers recognized that Calhoun’s work… was about degrees of social interaction. By reducing unwanted interaction through improved design of space — providing prisoners with individual cells or patients with independent living areas — crowding stress could be avoided. This had been the focus of Calhoun’s later research.”