Around how many things are killed by invasive species each year?

Many. Here is a list of invaders here in the U.S.

Eurasian collared dove

English sparrow

Starling

Rock dove

Nutria

rock python

Burmese python

Roseringed parakeet

Canary parakeet

Red crested cardinal

Many animals have been introduced with damaging results to the native wildlife. The eastern gray squirrel, for instance, was introduced to the U.K, Where it has decimated the red squirrel population. Foxes and other introduced species have played havoc in Australia with the small marsupial numbers.