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.

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.**

Fire Bears: caterpillars that can survive winter’s grip

**A woolly bear or fire bear on October 5, 2015, in a forest opening with abundant herbaceous vegetation for it to eat.**

If you could think of the top 10 most recognized caterpillars in North America, would the woolly bear be on that list? Probably. Many of us have seen the woolly bear , since childhood, watching them scurry across roads and paths on warm autumn days.

How many of us have seen the moth that the woolly bear transforms into? Not many unless you, like me, are a moth nerd. While not as dramatically colored as their caterpillar stage, the moths are nonetheless beautiful.

Fire bears

The genus name Pyrrharctia is from two Greek words: “pyrrh“, meaning “fire, flame colored, red” from the red-orange color, and “arktos“, meaning “bear” after the bear-like appearance of the fuzzy black bands. Fire bears.

Moth description

The woolly bear is the larval stage of the Isabella tiger moth (Pyrrharctia isabella), a apricot-yellow to buff-brown moth in the Arctiinae (Tiger and Lichen Moths). The forewings of the Isabella tiger moth are marked by darker veins and dark spots. The first dark spots, in a row about a quarter of the way from the apex, form a “W” shape (“angulate”) when viewed from above. The second set of dark spots is about three-fourths of the way from the apex. These form an irregular circle.

Along the wing tips are two rows of dark spots. The underwings are pale white in males and salmon-tinted in females. These also have black spots.

The top of the yellow to buff-brown abdomen is marked by a row of 5 or 6 roughly diamond-shaped black dots. The legs are black, but the first segment (tibia) of the forelegs is bright orange.

*Pyrrharctia isabella* on July 10, 2018 showing forewing markings.

Host plants

Woolly bear caterpillars feed on low-growing herbaceous plants like plantain, dandelion, dock, clover, and grasses and sometimes tree leaves. Weedy, mowed lawns, like mine, are perfect for them and other moth larvae, too. I’ve also seen woolly bear caterpillars eating swamp aster (Symphyotrichum puniceum) flowers and unripe meadowsweet (Spiraea alba) fruit in native wetlands.

**A woolly bear caterpillar is eating swamp aster (*Symphyotrichum puniceum*) flowers on September 19, 2017.**

Life cycle

The life cycle of woolly bear caterpillars begins when they hatch from eggs laid in early summer. They feed for the rest of the summer and go through four to six molts. In the fall, before cold weather sets in, they prepare to hibernate and wait out the winter under leaf litter. In the spring, they emerge from hibernation to feed a little while longer before going into pupation, after which new adult moths emerge. In my area, this happens during July.

In warmer climates, there may be two generations per summer, with the second generation going into winter hibernation.

Surviving the winter without freezing

Woolly bears’ bodies contain a lot of water, and if that water freezes, it will produce sharp crystals that can destroy cells. How do they get around that, especially in places where the average winter temperature is 15-20°F (-9 to -6°C) with lows sometimes reaching -60°F (-51.1°C)? That would be where I live.

Antifreeze, of course, which lowers the caterpillar’s freezing point. They also export water out of their cells, so if they do freeze, there will be fewer ice crystals that could burst the cells. They essentially dehydrate themselves and pump their bodies full of glycerol.

Weather forecasters?

There are plenty of stories about the woolly bear caterpillar and how the proportion of dark to orange on the bodies can predict how severe the coming winter will be. Unfortunately, those are just stories. Coloration is affected by age, how well the caterpillars fed during the summer, genetics, and the weather while the caterpillar was growing.

Festivals in honor of woolly bears

Many people love woolly bears and even devote festivals in their honor in places like New York, Ohio, and North Carolina.

Encouraging woolly bears

How can you help woolly bears thrive? Less frequent mowing and allowing some weeds to grow are two ways. Also, leaving leaf litter in places such as hedgerows and near the edges of yards provides a safe haven where they, along with other insects, can hibernate and pupate. In this way, you ensure that woolly bears will continue for years to come.

Halysidota tessellaris (Banded Tussock Moth): Identification and Life Cycle

In an earlier post, I wrote about Lophocampa maculata, a moth in the Arctiinae, distinguished by its fuzzy black and yellow larvae. These larvae later metamorphose into beautiful adult moths with a contrasting pattern of alternating bands of warm, muted golden-orange and darker brown markings with a reddish-orange tinge. In this post, I write about Halysidota tessellaris, the banded tussock moth, another moth in the Arctiinae.

*Halysidota tessellaris* caterpillar feeding on a crabapple leaf in late summer.

Identification

Like Lophocampa maculata, the larvae of Halysidota tessellaris are also fuzzy, but they are usually gray to dingy brown with long white and long black tassels. The adult moth, while similar in size to Lophocampa maculata, has translucent yellow forewings marked with slightly darker bands and irregularly shaped block-like cells that form a tessellated pattern. Also, there are two parallel blue stripes on the fuzzy thorax.

Life cycle

Across its range, larvae of Halysidota tessellaris feed on many species of hardwood tree leaves. Among these are box elder (Acer negundo), sweet birch (Betula lenta), ash (Fraxinus spp.), oaks (Quercus spp.), and many others. Adult moths take nectar and are pollinators of milkweeds (Frost, S. W. (1965) Insects and Pollinia. Ecology, 46. 556-558, paywall).

*Halysidota tessellaris*, a worn specimen, but the blue lines are prominent.

Similar species

Adults of the related Halysidota harrisii (sycamore tussock moth) are similar in appearance to Halysidota tessellaris. Where the ranges of Halysidota tessellaris and Halysidota harrisii overlap, genital dissection is necessary to determine the species. Halysidota harrisii larvae, which may be solid white, yellow, orange, or gray, feed exclusively on sycamore (Platanus occidentalis) leaves. The ranges of sycamore and the moth coincide closely.