eli5 how invasive species make their way across oceans,for example certain beetles coming from Japan to the US
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The vast majority of the time they hitch a ride on boats. Either some cargo or ship was infested/tainted or some person brought it over deliberately and things got out of hand.
For example, tumbleweeds are not native to the US, they are in fact from russia. They arrived in the US around 1870 because their seeds make their way into *everything,* such as the flax whose seeds were extracted, sold, bought, and shipped to south dakota. Then when the flax was planted so were the tumbleweeds which spread all over the great plains and american southwest in just a few years.
It’s often done deliberately. Rabbits aren’t native to Australia, but someone released a dozen so he could hunt them, now there are millions of them. A couple of centuries ago, a colonial gardener imported Himalayan blackberries. Birds spread them across the country. Now they’re everywhere.
It can deliberate or not.
Here’s an example of a deliberate one: Japanese Knotweed is a rather nice looking plant. It also has flowers that can be useful for beekeepers. It was imported for some use rather than accidentally.
The thing is that it is a weed. It tends to outgrow and outcompete indigenous plants killing them. It also secretes toxins from its roots which again kills anything that didn’t evolve alongside it.
It is ridiculously resilient and getting rid of it requires some rather extreme measures.
If you want another one: pigs. Back in the colonization era, many sailors would drop pigs on islands on the way to have a meat supply on the return trip. Pigs are incredibly good at surviving and reproducing. They also tend to ravage ecosystems as a result.
One that wasn’t deliberate: zebra mussels. They were basically stowaways on ships and made it to pretty much everywhere in the world.
Another non deliberate example is insects making it on imported fruits, vegetables, crops, etc.
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