Zebra mussels are a big problem in almost the entire US, with clogging of cooling systems at power plants an expensive consequence. Destruction of native fishing is a less visible consequence.

Kudzu is widespread in the SE US, and chokes orchards and pulls down power lines (and houses).

Russian Thistle (brought in a couple of hundred years ago) probably reduces usable grazing land by 20 or 30 per cent in parts of several states. (It was probably a contaminant in the "Russian wheat" brought in by early settlers. We'll keep the wheat, probably.)

The snails are eating houses and "pet pythons" are killing kids in Florida. The tropical snakes are causing really significant damage to bird and small native animal populations.

The big carp that are threatening a multi-billion dollar fishing industry in the Great Lakes may force Chicago to remove their canal that lets shipping from the lakes get to the Mississipi seaports, thereby shutting off a multi-billion dollar shipping industry.

And those #@$!% Shakespeare birds keep crapping poison ivy berries from the power lines in my back yard. (Free samples of the lovely ivy for anyone who wants to come and rip out a bunch.)

Armadillos used to be an insignificant problem when they came from Mexico without documentation, because they mostly stayed in Texas where the rest of us didn't care all that much; but they've now become fairly common in Nebraska and may have a foothold in S Dakota (~1200 miles from the border). They should all be deported if they don't immediately get a green card like all the new Brits do! I'd even suggest that the Armadillos should be required to find something useful to do to get their green cards, but the current more lenient standards could be applied to the ...

John