These are probably the berries of Italian arum (Arum italicum) in Troy, seen in September. Photo by Dana Wilde

Earlier this fall I was poking around by the brook, thinking about the plethora of life in crowded thickets, when down in the dry brown grass under goldenrod skeletons near a burdock hedge, a patch of red caught my eye. It was bright winterberry red, but close to the ground.

I knelt down, my knees got wet, and I parted some grass to find an unfamiliar oblong cluster of orange-red berries on a papery stalk lying almost on its side. Never seen anything like this, I thought, which doesn’t really mean much in my case because my knowledge of the natural world is cavalier at best. If it sticks to me while I’m walking in a field, I try to figure out what it is.

Several field-guide/internet-search episodes later, I was pretty sure I had come upon Italian arum, also known as Arum italicum, orange candle flower, lords and ladies, or cuckoo’s pint. It’s poisonous, causing severe irritation in the mouth if chewed, and can even be fatal. Its cousin is jack-in-the-pulpit (Arisaema triphyllum), which also has poisonous properties but can be eaten if properly prepared. Both mature plants have the spadex with “jack” peeking out, but the stalk of berries on this plant seemed to indicate it was arum.

Jack-in-the-pulpit is native here, but Italian arum is not. Arum is native to Eurasia and apparently escaped cultivation as an ornamental in North America, spreading from the South and Midwest to the Northwest and parts of the East Coast, where in places it’s deemed invasive.

Which brings up a burr that has been sticking to my sleeve unattended for a long time: What does “invasive” mean, exactly?

Definitions from reliable sources such as the U.S. and Maine departments of agriculture boil down to this: An invasive species is a species living in an area where it is not native and causing harm or disruptions (to environment, economy or health). Among plants, distinctions are made between native, nonnative, invasive, naturalized, exotic, translocated, and opportunistic native plants. (There are also weeds – plants people just don’t want around for whatever reason – and noxious weeds. I guess Mark Twain would call them weeds, and damn weeds.)

Some things are obviously insidiously invasive, and others you might never guess. I found out recently, for example, that some species of hawkweeds, which grow practically everywhere around here, are invasive. A spider species you may or may not have unknowingly laid eyes on, the European hammock spider, arrived from Europe in the vicinity of Mount Desert Island sometime in the last 50 years or so and has been spreading along the coast and disrupting the lives of other competing spider species.

Harmful species get here by human and nonhuman means. The spider probably came on a boat. The Maine Department of Agriculture warns people not to bring in Asiatic bittersweet and multiflora rose for holiday wreaths and garlands, no matter how pretty they look, because they escape readily and do serious damage to native plants.

The Maine Forest Service persistently warns against bringing firewood in from out of state, in order to keep out the Asian longhorned beetle, which is creeping slowly northeasterly, because it can decimate about 20 species of native trees. The emerald ash borer, which destroys ash trees and is already here, also spreads on firewood.

In the water, zebra mussels, which travel well on the hulls of boats and have caused enormous trouble in the Great Lakes, are in New England. European green crabs somehow got to the Gulf of Maine around 1900 and in recent decades have been exploding in population and eating shellfish resources. Variable-leaf milfoil showed up in the Northeast in the 1930s and in recent decades has caused vexing problems in central Maine lakes.

It may not be surprising to learn that house cats, who were probably brought to North America from Europe as much as 1,000 years ago, are still deemed invasive here.

Researchers say the Northeast has historically been particularly attractive to invasive species, for a variety of possible reasons. And as the climate warms over the coming decades, species that normally thrive in warmer southern areas are going to head this way of their own accord. The scientists are reluctant to predict exactly which ones will cause disruptions because so many ecological variables are involved. Changes in air and water temperatures, forestland damaged by increasingly severe storms, persistently drier or wetter conditions, and lengthening growing seasons will attract some species of plants and animals, and drive others out.

The explosion of deer ticks in recent years, turning time spent in the woods into a risk of debilitating disease, is just one example. Deer ticks are not invasive, since they are native here, but changing conditions have made them much more prevalent than they used to be.

My Italian arum, if that’s what it was, is not listed as even present in Maine, let alone as invasive. How did it get here? The short answer: A bird may have eaten a berry elsewhere, flew northeasterly and pooped a seed into our woods.

Life finds a way, to quote a monster movie.

Dana Wilde lives in Troy. You can contact him at naturalist1@dwildepress.net. His new book “Winter: Notes and Numina from the Maine Woods” is available from North Country Press. Backyard Naturalist appears the second and fourth Thursdays each month.