In this article opossums have been all but wiped out by snakes.

In my country we are overrun by possums (I guess they are close relatives of opossums), originally introduced for their fur, but now eating everything green in sight.

Is remarcable the over-cautious use of the word 'could' here.

There are tens of examples, from Achatina fulica to Aedes albopictus. Biologists study this since hundreds of years (and nobody listens).

Is it so hard to just put microchips that identify the owner into these animals?

Just imagine how easy it would be to punish the citizens releasing animals into the wilderness if micro-chipping was mandatory. No need to ban imports, nothing.

Micro chips can be removed, and some people just don't care the small probability to face a fine (that will not cover the 0,00001% of the economical damage caused in any case)