WHAT SHOULD WE DO ABOUT BENIGN EXOTICS?

by Whit Gibbons

November 13, 2016

Some introduced plants and animals such as fire ants and kudzu are classified as disruptive invasive species. In contrast, other well-known species not native to America such as apples and honey bees are viewed favorably and considered part of our culture.

In between are species that are considered neither detrimental nor beneficial; they do no apparent harm to people or native wildlife. I recently received questions about two of these benign exotic introductions.

Q: Can you identify a creature I found crawling across my sidewalk? It looks like a soft and slimy yellowish worm with black stripes down the body and an arrow-shaped head. I've never seen anything like it before. Is this some kind of invasive species? Should we destroy any that we find?

A: That is a type of flatworm known as a land planarian or greenhouse flatworm. Several species are known. One that is common in many areas was introduced into the United States from Asia more than a century ago.

They can stretch out to be over a foot long. They require moist conditions and are predatory on earthworms. They are slimy to pick up but do not bite or sting. They also can leave a shiny, silvery trail where they have crawled.

They sometimes lay eggs but also can reproduce by breaking off the rear portion of the body and crawling forward, leaving the end piece sticking to the ground to become another individual. That’s bizarre enough, but they also have no circulatory or respiratory system, no legs and no external or internal skeleton. They are so abundant in New Orleans that a colleague of mine caught land planarians for lab demonstrations in zoology classes at Tulane University.

As they are ubiquitous in warm, humid habitats and have been around for decades, trying to get rid of them is probably not worth the effort. I’m not aware that they do any harm environmentally, aside from eating a lot of earthworms.

Earthworm farmers and greenhouse owners, where earthworms are important for soil aeration, would disagree that they cause no harm and might want to eliminate them. Ironically, however, most earthworms are not native to America either, so who’s to say that land planarians shouldn’t be here also? Plus they are kind of cool creatures to show off to folks, as my grandsons often demonstrate when they discover one in the backyard.

Q: I live in southern Georgia and am wondering what kind of gecko I keep seeing. They are all over my yard, house and garage. They are super cute.

A: That is a Mediterranean gecko, one of our most widespread nonnative lizards. They are recognizable by the small tubercles visible all over the body and tail.

They were first reported in the United States in Key West, Florida, in 1910, probably introduced from cargo ships. They have made their way from southern Florida into urban areas in many parts of the South and Southwest over the last century, generally as an unseen hitchhiker on vehicles.

Most Mediterranean geckos live around man-made structures, so they have little or no impact on natural habitats or native wildlife. They come out mainly at night and are especially prevalent around houses or buildings in the vicinity of an outdoor light.

To my knowledge, they are totally inoffensive not only in regard to our picking one up but also to pets. One neat feature is that during their breeding season the eggs are visible inside the body of females. Mediterranean geckos are indisputably interesting little animals to have around.

We have many other benign introductions from other continents that live around us and cause no appreciable environmental harm. In fact, the number of nonnative species that thrive here now exceed the number of native representatives of some taxonomic groups in many regions. And the disproportionate ratio of exotic to natives continues to grow. We might as well learn to enjoy them.

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