Finding Williams’ Tiger Moth in Minnesota

William's tiger moth on a gravel road in northern Minnesota
The Williams’ Tiger Moth (Apantesis williamsii) I found in the SNF. Photographed on July 20, 2018.

In a previous life, I searched for and documented rare plant species. But I was always curious about everything in nature, so I made it a point to learn as much as I could about all the things in the forests, glades, lakes, and swamps I explored. Sometimes I would make an interesting discovery, like the moth in the above photo.

I find a new moth

A few years back, while on a rare plant survey, I found a tiger moth that I later identified as Apantesis williamsii (Williams’ Tiger Moth). I found the moth in Cook County, Minnesota, in the Superior National Forest (SNF). It was simply lying in the middle of an old logging road just waiting to be found, I guess.

I’d never seen a moth quite like this one. I photographed it (I would have anyway no matter if it was new to me or not) and took some notes about the surrounding area. Then I GPS-ed the location, which is about 20 miles south of the US-Canadian border.

Because blueberry pickers were using the road that day, I carefully moved the moth to a safe spot. Then I got back to that day’s mission, searching for rare plants in the forest and the rare Nabokov’s blue butterfly (Lycaeides idas nabokovi). It might have been in the area as its larval host plant, Vaccinium cespitosum (dwarf bilberry), grew nearby in a prescribed burn. I found plenty of dwarf bilberry that day, but no sign of Nabokov’s blue butterfly. Not even a caterpillar.

Not a common species in Minnesota

Apantesis williamsii is uncommon in Minnesota. It appears that there are only two records before 2018. One record is from Cook County, the same county where I found this one, up in the northeastern corner of the state. The other is from Lake of the Woods County in the Northwest Angle, right on the US-Canadian border, found in 2017.

Since then, additional sightings of Apantesis williamsii have been made. Two other sightings (here and here) were made in Minnesota in 2018, but from northern St. Louis County, about 50 miles west near Ely, and also close to the Boundary Waters and Canada.

Apantesis williamsii range map. The distribution of Apantesis williamsii is concentrated in the Cordillera.

Globally secure

This is not a rare species globally, but based on the small number of sightings, it appears to be uncommon in Minnesota. Most records of Apantesis williamsii are from the Cordillera, starting in Saskatchewan, Canada, and then south through Montana, Idaho, Wyoming, Colorado, Utah, California, Nevada, Arizona, and New Mexico in the western US. It occurs sporadically elsewhere, with scattered reports from Alberta, Manitoba, Ontario, Quebec, and New Brunswick in Canada, and in Michigan and Maine in the US.

Habitat preferences

In the main part of its range, Apantesis williamsii can be found in mountain meadows at middle to high elevations. It also occurs in quaking aspen forests and dry coniferous forests with sandy soil. The latter isn’t too different from the site where I found it. This was in a forest of aspen, birch, spruce, and fir with some jack pine and white pine on sandy soil. The weather is also cool in the summer, although climate change may upend that.

What does it it eat?

Larval food plants of Apantesis williamsii are not known, but it may feed on low-growing herbaceous vegetation like other species of Apantesis.

Something else I found on my way to the mailbox

Red-belly snake (Storeria occipitomaculata) sunning itself in my driveway.

Yesterday was warm, humid, and a little sunny. It was nice, especially after last week when our evening temperatures went below freezing. Some of the little animals that live here must have felt the same way. In one of the tire tracks in my drive was this tiny red-bellied snake (Storeria occipitomaculata) sunning itself on the warm gravel.

Red-bellied snakes are harmless, non-venomous, and eat small insects. They’re rather docile and don’t seem to get too upset when handled. I often find them in mounds of old hay and leaves where the decomposing plant matter generates heat.

The Minnesota DNR has a webpage on red-bellied snakes here.

Going in circles

A Stigmella moth leaf mine in a bristly blackberry leaf.

While out one afternoon in my tamarack swamp hunting for dwarf mistletoe, the subject of a future post, I found this leaf mine in the leaf of a bristly blackberry. The blackberry is possibly Rubus flagellaris, but I’m still working out the identity of the species.

The leaf mine bears a strong resemblance to the leaf mines made by the larvae of the moth Stigmella villosella (Family Nepticulidae). Stigmella villosella is a specialist on Rubus species. The adult moths are minute with a wingspan of only 3 mm.

I doubt I’ll see this moth at my lights, but maybe next year, if I find an active leaf mine, I could raise the larva to maturity. I’m going to give it try anyway.

Another Rubus leaf, but without leaf mines, just a few holes all near the midvein made by some unknown insect.