Hello hello! Today is the final story in our flora & fauna of Boise series. The first looked at the birds of Boise. The second looked at the flora of Boise. Today, we're looking at the invasive species of Boise. This series was written by the wonderful Amanda Patchin. Enjoy! - Marissa

Say the phrase “invasive species” on the streets of Boise and you might hear a dumb joke about Californians moving to the valley. But when it comes to actual invasive species, Boise does have a few worth talking about. And most of them ended up here through someone’s well-intentioned but disastrous attempt to do something good.

An invasive species is more than just an organism imported from elsewhere. To qualify as “invasive” it must be non-native, overpopulated, and harmful to the ecosystem. Non-native is pretty easy to identify. Any plant or animal that did not historically live here is not native to the region. Simple, definitive. But there are plenty of non-native plants and animals that so well-adapted to our region that it is surprising to realize that they are not from around here.


Say “squirrel” in Boise and you will be assumed to be talking about the little gray and brown critters that live in trees and run across streets. Say “squirrel” in one of the many rural communities around Boise, and the assumption will be that you are referring to ground squirrels.

Photo by Brittney Weng

Ground squirrels are native to the Boise region and are full of personality as well as danger. Ranchers historically dislike them because of the danger their tunnels pose to horses and cows who may step into one and break a leg. Ground squirrels are generally fair game for hunting and going “whistle pig” shooting is a rite of passage for many young Idahoans. However, some subspecies are endangered and therefore are protected.

The greater danger of ground squirrels is that they do serve as a reserve for the bubonic plague. Yeah, that plague. The black death. The plague that killed half of Europe in the 1340s. If you do take up whistle pig shooting, be sure not to touch or allow a pet to touch the dead animals! In 2012 an Oregon man contracted the plague after fleas from a dead ground squirrel got on his dog and then on him. He survived but not until he had lost his fingers and feet to progress of the disease.

Photo by Miguel Vieira on Flickr

To Boiseans, the fox squirrel is definitely more familiar than their plague-bearing cousins. Unfortunately, they are not actually a native species, although they are thriving in Boise. Whether or not they qualify as invasive would depend on an assessment of whether or not they are overpopulated and whether or not they are harmful to the ecosystem. They certainly do not appear on the official Idaho list of invasives, however, my garden would like a word! Because they are hungry from their winter hibernation, the springtime sees them digging up freshly planted seeds for a quick snack before the trees send out their shoots and leaves.

There are native red squirrels that inhabited the Boise area long before Europeans arrived, however, their populations are under pressure because of the prevalence of the fox squirrel. It is easy to confuse the two, unless you have ever seen a red squirrel next to a fox squirrel, when the fox squirrel’s superior size would forever distinguish them. You can spot red squirrels up in the mountains running up and down the big ponderosa pines and you can spot fox squirrels up on my porch investigating the cereal bowl my son left out this morning.


It may be a relief to know that Boise’s most dreaded, most hated, most painful weed is an invasive species and thus a fair target for any and all methods of destruction. Fox squirrels are kinda cute, if you forget that they are essentially rats with fuzzy tails, but no one ever saw a goathead and thought anything but curses.

The weed itself is rather innocuous looking, just a flat and spreading little mat of green with tiny yellow flowers in the spring, but it grows painful little burrs that make stepping on LEGO feel positively gentle by comparison.

I first met the dreaded goathead while playing volleyball in a friend’s backyard way back in the early 2000s. All along the cultivated edge of their sand court, the spiny little monsters came creeping in. The greatest difficulty in any attempt to eradicate the creeping vine, is how hardy and durable it is. The roots of the puncture vine have many tiny hairs allowing it to take advantage of the barest scrap of moisture. It can thrive in loose sandy soil, in compacted soils on roadsides, and equally well in fertile and rich soils. It is found in gravel parking lots, in the untended bits of dirt between sidewalks and streets, in the disturbed soils of a new construction site.

Organic farmer and permaculture enthusiast Tao Orion argues in her book Beyond the War on Invasive Species that we must consider the ecological niche an invasive plant occupies before attempting to eradicate it. When I first read her book I excitedly went to my neighbor, Keith, who has been fighting a steady war of attrition against the patches of goathead that plague his biking routes. All my enthusiasm faded though, when our conversation made clear that there was no proper way to replace goathead with an equally adaptable competitor. It survives because it lives where there is virtually no competition.

Credit Boise Goathead Fest

The goathead arrived in Boise with European settlers. There is a popular rumor that they were deliberately imported as a preventative measure against runaway prisoners around the Old Idaho Penitentiary. I first heard it while working at the old Owyhee Hotel in the late 90s. There is no documented source for this rumor and according to Boise State Radio, we have only been sure of goathead’s presence in the area for a little over forty years, which would seriously discount the Old Pen story!

Most probably goatheads arrived stuck to an animal's fur or embedded in a bike or car tire. Spread has been attributed to sheep carrying the burs in their wool, which would fit with the rich tradition of Basque shepherding in the foothills, but still does not account for the relatively late documentation of the nasty little vines.

No discussion of goathead would be complete without acknowledging eradication attempts. They are pretty sturdy little things and so the best approach is to dig them up at the root. An old screwdriver is perfect for loosening the solid around the root and ensuring you get the whole thing.

Credit Boise Goathead Fest

It takes repeated weedings to really clear out a patch and once you start working on a spot you should plan to spend several years revisiting it to pull up new vines. Spring is best for this work but a late Autumn visit will help decrease reseeding.

Boise’s annual Goathead Festival is a great way to learn more and get some practice in!

Credit Boise Goathead Fest

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Poison hemlock

As horrible as goatheads are. As much as we loathe them when we step on them or when we find them in the paws of our limping dogs or when they pop all the tires on all the bikes, they are not nearly as terrible as the next invasive species on my list. I find fox squirrels annoying when they eat the freshly planted seeds in my garden, I find goatheads painful when they pierce the bottom of my thin-soled moccasins, but poison hemlock can literally kill you.

Credit Luciana Armilio Thornton

In 399 BC a short, stubborn, ugly man was sentenced to death for corrupting the youth. Socrates was an annoyance to the establishment of Athens and, despite the declaration of the Delphic Oracle that he was the wisest man alive, he was put to death for questioning everything. His story, as told by Plato, is fascinating for the rich curiosity he constantly showed, his passionate enjoyment of the pleasures of friendship and intellect, and for his steady insistence on acknowledging the limitations of knowledge.

Accused of sophistry and denial of the gods he defended himself (quite eloquently) by saying he spoke plainly and that he was the defender of the gods for he rejected the crude anthropomorphic tales told about them. The politically tense situation in Athens assured his conviction and his death sentence was to drink brewed poison hemlock.

The death of Socrates. Illustration source: poison.org

Growing up in Idaho, I thought hemlock was a kind of pine tree. And, in fact, the Western Hemlock is a conifer. The lovely, soft branches of the Western Hemlock dot the slopes of North Idaho mountains. Technically “Tsuga”, hemlocks are so called because they are supposed to have a similar scent to poison hemlock. It would be dangerous to attempt the comparison though, as even the smell of a poison hemlock can make a person ill!

Like goatheads, native to Eurasia, the poison hemlock came to Idaho from Europe. Its native range includes North Africa as well, but it is distributed across much of the world and can even be found in New Zealand and Australia. It grows in disturbed ground and particularly like wet, heavy, and poorly drained soils. Thus, it can be found along ditches and streambeds even in a dry climate like ours.

Credit Luciana Armilio Thornton

Poison hemlock is in the carrot family and its leaves look like carrot tops and parsley. Green with reddish-purple spots, the stems are sturdy and allow it to grow very tall. Poison hemlock is classified as invasive but it is far too dangerous for amateur attempts at eradication. The smell can sicken and kill and it takes only a few leaves worth of its dangerous alkaloids to shut down the central nervous system of a mammal.

I’ve personally spotted poison hemlock in the Cottonwood Creek drainage near the Military Reserve. Definitely watch out for it along any wet trails and give it a wide berth!


There are plenty of mites and beetles and bugs on the Idaho Invasive Species list, there are also varieties of catfish and carp and even a piranha! However it is Walleye making the news today.

Walleye are not native to Idaho and, while they can easily survive here and are managed in small areas around the state, they are predatory to native fish like perch, and damaging to perch habitat.

Walleye caught in Lake Pend Oreille. Source: Idaho Fish & Game

What is surprising about Walleye is that it is appearing in bodies of water it has no natural access to. Unless Walleye have secretly been developing land transport systems for themselves, it seems that someone has deliberately been introducing them into isolated lakes.

Just last week, an angler reported catching a walleye on the Snake River below Swan Falls Dam. Fish and Game officials say this is the third body of water (Lake Cascade and Lake Lowell are the others) this spring where walleye have been encountered.

Walleye caught near Swan Falls. Source: Idaho Fish & Game

It is important for citizens to be aware of invasive species and sensitive to their effects. Idaho’s list includes plenty of plants, bugs, and critters to be aware of and it is wise to be attuned to the possibility of accidentally transporting mussels, pox, or blight into your community. Still, not every introduced species is invasive.

The lovely Gingko trees lining Capitol Blvd are native to Asia but well adapted to our City of Trees. The potato is native to Peru, but nutritious and profitable for Idaho. And the beef we eat is the long descendant of the mighty Aurochs that roamed the mountains of Europe.

Perhaps a goathead in your foot is the ecological price of enjoying a well-grilled steak.

Thanks for reading!

With love from Boise,

Amanda Patchin

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A weekly newsletter & podcast about what's going on in Boise, Idaho. Every week we share stories about people, places, history, and happenings in Boise.

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