Fish and visitors stink after three days, Ben Franklin famously said, and we have recent evidence of his wisdom in Minnesota while hosting emerald ash borers and the Japanese rock pool mosquito.

They were uninvited guests. The emerald ash borer, first found in St. Paul May 13, came from Asia. Initially identified in the United States near Detroit in 2002 (like Detroit doesn't have enough problems?), scientists guess that it was probably here for 10 years before that. Green ash, black ash, white ash, blue ash — the beetle is an equal opportunity pest, and it's a slow death for the tree — two or three years.

Like the ash borer, the encephalitis-carrying Japanese rock pool mosquito is an accidental import. It's in at least five Minnesota counties, and as I type this with three mosquito bites on my right hand and two on my left, I wonder where I've been lately and how to possibly tell a Japanese mosquito from a Yankee bug.

Species have been moving around the globe since there have been species, and sometimes, unlike the two mentioned above, humans move them on purpose. Ecologists use the term "introduced species" for this effort, and there have been spectacular mistakes.

The house sparrow, for example. Prior to the 19th Century, it was found only in Eurasia and North Africa. In 1851-52, 100 birds from England were intentionally and successfully introduced to Brooklyn, N.Y. In the next few years, releases followed around the country, including St. Paul in 1876. The birds were imported to eat insects (some said they would gobble up the horse dung stinking up the streets), but the pest controller became the pest.

"Without question the most deplorable event in the history of American ornithology was the introduction of the English Sparrow," wrote W.L. Dawson in "The Birds of Ohio" in 1903. By 1887 states had established house sparrow bounties (2 cents apiece in Illinois) and "sparrow clubs" were formed to shoot the rascals. Neither worked. House sparrows are now among the most numerous songbirds in the country, although some evidence exists that the birds have been in a slight decline since the rise of monoculture farming practices in the 1960s.

House sparrows vie for most numerous honors with the European starling, also an introduced species. The starling's history in the United States is much more romantic than eating horse poop, however. A man named Eugene Schieffelin, perhaps under the influence of Anglophilia, brought starlings over in 1890 in what has been described as the first (and last) effort to introduce all the birds mentioned in the plays of William Shakespeare to the United States.

"There's a special providence in the fall of a sparrow," said Hamlet, but Schieffelin's motives with starlings were probably more along the pest-control lines of the sparrow-lovers, and the results were the same.

Lest we place too much blame on bird-lovers for what we now see as boneheaded moves, there have been many fish (such as carp) and plants (such as dandelion) that we'd now rather not have around in large quantities.

And lest we find ourselves guilty of the sin of presentism, as historians call it, where would sportsmen be on a fall afternoon in Minnesota without the Chinese ringneck pheasant or the German brown trout? And, as we sit under the shade of the Minnesota state tree, the Norway (red) pine, let us remember that it is not native to Norway at all; white settlers mistakenly thought it was the pine they grew up with in the Old Country.