Sterilization is tricky when you have retractable testes.
Pablo Escobar smuggled something very dangerous that is still having a devastating affect on parts of Colombia: hippopotami.
Four hippos that were once pets of the notorious drug king have multiplied to more than 80... and could swell to almost 1,500 in the next two decades if something is not done now, scientists claim.
When Escobar was killed in 1993, his menagerie of exotic animals was rounded up and relocated to zoos, etc; but authorities were wary of trying to capture the one male and three females, a famously aggressive species, so left them to roam free.
Nearly three decades later, their offspring have colonized the Magdalena River and surrounding lakes, and are threatening to spread even further, according to an environmental impact study in the journal Biological Conservation.
While they have to contend with predators, drought and territorial competition in their native Africa, humid and food-plenty Colombia has turned out to be something of a "hippo paradise", which has helped their population to grow unchecked.
There have been many blocks to the tardy effort to control the invasive species: for one, they are rather beloved by locals, and are considered a sort of mascot for the area. They have become tourist attractions and feature heavily on local souvenirs. One early government attempt to cull the mammals had to be halted due to public outcry.
Capturing and rehoming them is extremely difficult, and not just because of their infamous bad temper. Measuring the same size as a family sedan and weighing a good deal more, they are very awkward to transport. Plus African nations are wary of adopting unpredictable foreign-raised animals and putting their own native population at risk.
Sterilization has also been tried, but may be even more difficult still, thanks in no small part to the fact male hippos have retractable testes.
According to David Echeverri Lopez, who led that effort, the dangerous, time consuming and costly approach is hardly worth it; he is only able to castrate one male a year, while the population is growing at a rate of 10 percent annually.
Now, their impact is starting to be felt. Infamously the most deadly animal on the African continent, one Colombian rancher was lucky to escape with his life when he was attacked last year; a hippo bit the 45-year-old and threw him through the air, breaking his leg, hip and several ribs.
Also, a separate study carried out last year on their habitat found huge blooms of algae and bacteria fueled by the animal's feces, causing the water to approach toxic levels for native fish.
The only way of halting the invasion is to begin killing the animals, however reluctantly.
"Nobody likes the idea of shooting a hippo. I do not like it," report author Nataly Castelblanco-Martínez said, per the Washington Post. "But no other strategy is going to work."