As an aging gardener, I figure I know a lot. Or at least I have forgotten much. But here's something I never considered: those plump earthworms that we want in our gardens and red robins love to eat aren't native to North America.

Yes, they are invasive species, brought over from Europe by the colonists and other immigrants with the plants they brought and in ship ballasts.

I learned that interesting bit of trivia at a recent master gardener class taught by Dawn Pettinelli, who manages UConn's Soil Nutrient Analysis Lab and the Home and Garden Education Center. If one ponders soils, and master gardeners do, the invasive worm theory makes sense. The native worms wouldn't have survived our ice age and glaciers.

So, the earth worms we think we know and love, like common night crawlers (Lumbricus terrestris) and red wrigglers (Eisenia foetida), came from Europe. There are at least 14 such species in northern New England, according to Dr. Josef Gorres at the University of Vermont. They seem pretty compatible - we know they turn organic matter into nutrients for plants and their tunnels help aerate the soil, so we consider their presence a sign of healthy garden.

But, there are aggressive invasive earth worms in our midst, and it doesn't look pretty. The Crazy Snakeworm (Amynthas agrestis), which looks like an energetic little snake, is devouring top soils and mulch, to the detriment of our plants. These Asian worms live on top of the soil, not in it.

It's not good for our landscapes or our lawns, and it's even worse for the native Eastern deciduous forest, where the understory is being destroyed and habitat for native forest wildflowers is disappearing, making it easier for invasive plants to take over. Insect and animal species that live in the forest duff are suffering, too.

Dr. Gorres points out that since we think earthworms, in general, are up there with Mom and apple pie, we haven't realized the indirect consequences of the invaders. He says we need to avoid introducing even the European worms into our native Eastern forests.

So what's a responsible gardener to do? Since vermiculture (that's tech-speak for feeding your kitchen peelings to composting worms) and using worm castings (that's polite gardener-ese for worm poop) are all the rage, it means knowing what kind of worms we're using and handling them properly, says Pettinelli. And yes, the UConn Home and Garden center will help home owners identify worms.

If you're in the market for composting worms, ask for them by the Latin name, E. foetida. Avoid any worm that has "crazy" or "jumper" in the common name, even if they are a bargain. The Crazy Snake worms are an annual species, which means the adults shouldn't survive our New England winters. Their eggs might, though, especially in compost piles.

If you buy or use worm castings, know the source, too. Worm eggs can be mixed in with the castings.

Once it warms up, don't apply mulch too deeply around plants. Telltale signs of the Asian species include clumps of worm castings on top of mulch, rapidly degrading mulch and anemic plants that are otherwise in the right location and soil and are properly watered. There could be a very happy colony of Crazy Snake worms living at the plant's base.

It's not that hard to spot a Crazy Snake worm wriggling away, but don't think that grabbing and drowning it will solve the problem. The critters can reproduce from a broken tail piece, so you've just done them a favor if you pull one out of the ground. There aren't any organic controls or natural predators identified yet, so collect, bag and throw away the castings, but don't put them in the compost pile. If you can catch the worms, toss them in a solution of 20 percent vinegar and 80 percent water.

Since worms don't migrate that quickly, at least not the European ones, we humans are to blame for spreading them. We do that by transporting plants and soil, trekking into woods, dumping our left-over fishing worms in the garden or tossing spent potting soil and cast-off horticultural plants on the edge of the forest.

You can learn more from the UConn Home and Garden Center website, www.ladybug.uconn.edu, or stop by the UConn booth at the Connecticut Flower and Garden Show, which runs through Sunday at the Hartford Convention Center. There are free soil pH tests for anyone who can find their lawn or garden soil under the snow.

While it's good to get a thorough nutrient analysis every couple of years, Pettinelli says the pH test is the most important test for both garden and lawn soils. That's because nutrient availability is dependent on a soil's relative acidity. A proper pH level can make all the difference between a healthy plant and a stressed, sickly one.

Suzanne's weekly "CT Outdoors" radio show is on WLIS 1420 AM and WMRD 1150 AM from 1 to 1:30 p.m. Saturday and from 7 to 7:30 a.m. Sunday, or listen to archived shows in the On Demand section of www.wliswmrd.net. Reach her at suzanne.s.thompson@sbcglobal.net.