200k doesn't seem like that much. Rats aren't very big, and Barcelona is a pretty large city, with a population of about 1.5M humans. I would have expected more, having grown up in a rural area where there's a lot more mice, rats and other critters than one per 7 humans.
Leaving aside the pest aspect (and I'm sure it's all too real in many places), rats are fascinating creatures with a sharp, pragmatic intelligence, loads of adaptability, and social behaviors that we primates can very easily recognize and relate to.
I have seen rats perform clearly abstact thinking, brewing up complex ad-hoc plans, and show stunning degrees of spatial awareness. I have been lied to by a rat, who seemed to have worked out a decent model of my expected behavior. Which I promptly delivered - the rat won.
And these were domesticated rats. I should be surprised if their wild cousins weren't up to even more hardcore mental trickery.
This reminds me of the saying <i>"You're never more than 6 feet from a rat"</i><p><a href="https://www.bbc.com/news/magazine-20716625" rel="nofollow">https://www.bbc.com/news/magazine-20716625</a>
I lost count after 200,003 rats :)<p>Do rats serve a useful (for us) purpose there? If not, can we release a rat specific poison or is that impossible without harming the entire ecosystem?
A bit of context that is perhaps relevant. As some of you know, there is a political conflict between the central government of Spain and the local, pro-independence Catalan government. El País, a newspaper published in Madrid, has quite explicitly taken the central government's side a few times. I wouldn't be terribly surprised if this bit of news was singled out for publication because it's about there being potential health and safety issues in the main city of Catalonia.