I've never seen an alien, besides those in videogames or movies where they invade the Earth. "Independence Day" (1996) is the last film I saw about these beings. This movie shows the bitter hours spent by the USA citizens, government and army dealing with a group of invader aliens, who one day invaded the Earth.
This scenario seems unlikely because we have no evidence even that life exists on other planets. However, we're now fighting against invaders capable of destroying ecosystems, injuring humans or causing enormous economic losses: invasive species.
Unlike aliens, invasive species do not arrive by themselves. They are almost always associated with humans. We transport them accidentally or on purpose, from their place of origin to places where they previously did not exist.
One example is the Argentine parrot (Myopsitta monachus), a native bird to South America and it is very popular as a companion animal due to its striking colours and resistance. This bird has overcome more than 5,000 km of tropical forest between its natural distribution region and Mexico, transported by humans.
It is believed that once in the country, some individuals escaped or were released. Because they have no predators, they began to reproduce uncontrollably, leading to ecological problems. Indeed, the Argentine parrot transmits diseases to other birds and compete for food with them. Also, over-consume vegetation and their nests can damage utility poles, which affects the supply of electrical energy for homes.
There are numerous other biological invasions cases, all coinciding in causing negative impacts on ecosystems, human well-being and the economy. That's why some governments consider biological invasions a matter of national security, as the alien invasion we see in "Independence Day". Like in the film, preventing and mitigating the damages caused by biological invasions is required a huge coordinated effort between scientists, society, governments and even the army. In fact, in scientific literature, invasive species are also called "Invasive alien species". We can all contribute to this fight by not buying or transporting non-native species and responsible pet ownership. Let's not let them invade us.
Autor: Esteban Aceves Fonseca
Institute of Marine Sciences and Limnology, UNAM
s