2016 September 17
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These plants are one of the signature species in the area, and figure heavily in the tourist trade – Thimbleberries, Rubus parviflorus. They are primarily a cool-weather western species, growing along the west coast at increasingly higher altitudes as one moves south. They mostly don’t grow east of the Rockies, but somehow we ended up with a disconnected population along the southern and western shores of Lake Superior[1]. They grow quite lushly, particularly on the north side of roads, alongside woodland trails, and at the edge of wooded areas. Here’s a patch on June 13, 2016, right at the height of their blooming season:


The leaves are pretty distinctive, they look kind of like maple leaves, only bigger and a more lurid shade of green.


The blossoms start out looking like this when they first open:


and later end up like this after they’ve produced their pollen:


After the blossoms are pollinated, they take close to six weeks for the fruit to ripen, these are from July 26, 2016:


The ripe fruit resembles raspberries, except that they are softer and easier to squash, and also have a slightly velvety texture as if they are covered with short fur.



The core of the fruit pulls out, leaving this behind after the berry is picked:


Like a lot of wild fruits, the berries are extremely tart. They can be eaten plain, but it is kind of a puckering experience. The thimbleberry jam that is made for the local tourist trade runs almost 50/50 sugar/berries. The jam is quite expensive because it takes a long time to pick enough berries (The Jam Lady, up about 30 miles north of here in Eagle Harbor, is asking $12 for what looks like a half-pint jar). Some of the jam producers pick their own berries, while some of the largest producers mostly buy their berries from free-lance pickers, who roam all over the Keeweenaw[2]. One of the other big thimbleberry jam producers is the Jam Pot Bakery, which is operated by the monks of the Society of St. John, and has become a significant tourist attraction[3].

Generally the thimbleberries do very well, but sometimes there are disease and pest problems. Probably the most significant are the Thimbleberry Gall Wasps, Diastrophus kincaidii. These only arrived in the Lake Superior region in the mid-to-late 1980s, and by the 1990s they were severely knocking back the thimbleberry production. The galls start out as a solid swelling on the thimbleberry stalk, where the wasp larvae are growing inside.



The gall eventually kills the stalk, and in the spring the wasps leave behind a dried-out gall:


The wasps don’t kill the plant outright, but they infest and destroy first-year growth, and since stalks don’t bear fruit until the second year, this can really put a crimp in the fruit production. When the wasps first got into the area they dramatically reduced fruit production, and the competition for fruit among the jam producers was pretty fierce for most of the late 1990s and early 2000s. Things have settled down now, and while the galls are still plentiful the plants have evidently developed enough resistance to the wasps that they can still produce significant fruit.

[1] I expect that what happened was that, during the last ice age, the margin of the ice sheet was the sort of cool, wet environment that thimbleberries like, and so at the time they grew all the way from coast to coast. But then, when the glaciers melted back, the Great Plains area became too dry and too hot in the summer for them. But, since Lake Superior kept the Upper Peninsula cool and wet, the thimbleberries were able to survive here after they died back elsewhere.

[2] For a fairly in-depth discussion of the Keeweenaw Thimbleberry Jam industry, check out this document: THIMBLBERRY JAM PRODUCTION IN HOUGHTON AND KEWEENAW COUNTIES, MICHIGAN (pdf file). This is an MS thesis from 2003, prepared by a forestry student here at Michigan Tech.

[3] The monks’ products are good, but much too expensive for daily consumption. They are clearly targeting the tourists.

2 Responses
  1. Mary Peed permalink
    September 19, 2016

    Last time I was at the monks, the jam was near to $20 a half pint. You can find half pints at the local farmers markets for $10 a half pint. And yes, it’s still pretty expensive for regular consumption. But like some other local specialties (pastys, nisu, kuchen bread, juustoa) it says “COPPER COUNTRY”!!

  2. Kyle Pellar-Kosbar permalink
    September 19, 2016

    The monks wild bilberry jam is totally worth it though. (Call me a heretic, but Thimbleberries never did much for me.)

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