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Non-human immigrants

As Thanksgiving draws near, and we hear tales of “The First Thanksgiving”, and explanations of the tales’ inaccuracy, my mind turns to other immigrants. For better or worse, humans from the Old World journeyed across the Atlantic Ocean, and carved lives for themselves here in the New World. But humans are far from the only species to have done so.

Once upon a time, the Americas had no grasshopper species – genetic evidence suggests that our North American “Bird Grasshoppers” are descended from West African grasshopper immigrants which flew across the Atlantic. While this sounds rather far fetched at first, it become less so, when realizes that Schistocerca grasshoppers flew from West Africa to the Caribbean in 1988…
A decade before, in 1977, related Bird Grasshoppers flew from Central America to Hawai’i with the help of a strong storm system, where they have since caused problems. Most invasive species, though, have made use of human help to travel such vast distances.

Here in Montana, we have no shortage of invasive weeds, and many of them are immigrants that are here thanks to human activity. Spotted Knapweed stowed away in seed shipments, Mullein, Plantain, Dandelions, even Stinging Nettle All came over with European settlers, and were put to many uses.
On the other hand, Spotted Knapweed, both a more recent import and a more noxious weed, was not deliberate. Its seeds stowed away as contaminants in seed shipments, and the species has since spread through much of North America.

Honeybees, as well, are newcomers to this continent – deliberate introductions, unlike many insects. According to Thomas Jefferson, Native Americans called the honeybee the “white man’s fly,” and thought it associated with European settlements. While North America once had its own native species of honeybees, they went extinct long before the European honeybee made American landfall in the 1600s.

Our homes’ infestations of Cluster Flies? I suspect their introduction was less than planned. Likewise, European Paper Wasps, Asian Longhorned Beetles, and Multicolored Asian Ladybeetles were all stowaways who have done quite well for themselves here in the Americas.

Immigrant species aren’t all bad, however. Indeed, I’m very glad we have immigrant species – for every “bad” one, there’s another out there, somewhere, that presents a solution. Biological control can be a wonderful way to put imbalanced systems back into stability.

If you’re interested in learning more about what species became immigrants alongside European colonists, consider browsing Nunn & Quian’s “Columbian Exchange“. It gives a good summary of what foodstuffs, diseases, and technologies arose from immigrant species on both sides of the Atlantic.

Some of my favorite insect immigrants – flies which help control knapweed.
These two adults died with the coming of the cold,
but their young are safely overwintering inside seed heads.

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