Discovering Minnesota’s Diverse Moth Species

**Phalaenophana pyramusalis** (dark-banded owlet, Family Erebidae, Subfamily Herminiinae).

How many moth species does Minnesota have?

When I first started moth hunting in 2017, I had no idea how many species of moths live in Minnesota. My first experience with Minnesota’s moth numbers was from a moth survey report. There had been a Minnesota DNR moth survey of state parks from 2006 to 2008 along the eastern edge of the state. Its purpose was to document moth species present before LDD moth (Lymantria dispar dispar) control efforts.

Their final list, representing just a small portion of the state, was 768 species, although they believed that statewide, there are about 2,200. I wondered how many of those moths might be where I live.

So many moths are tiny

Early on in my mothing I noticed there were many tiny moth species. I found some moths the size of a thumbtack. Others are smaller than a grain of rice, like the three species below.

*Epermenia albapunctella* (Epermenioidea)

Identification is not so simple

Most people are familiar with the larger charismatic moths, like the luna moth or one of the sphinx moths. But for many of the moths out there, they are just moths. This is understandable. Identifying anything to species is not always easy. With moths, this task is even more challenging given their variety of sizes, colors, and often subtle differences in wing patterns. To make matters worse, some species exist in different forms or look like other species.

Acleris (Superfamily Tortricoidea, Family Tortricidae) is a good example of a genus with intraspecific variation. Some species even resemble others within the genus. I’ve included two photos of Acleris celiana showing two of the forms it exists in. There are also photos of other Acleris species, some of which resemble each other.

So, is that the final count?

By the end of 2019, I had identified 541 moth species. It seemed to me this was close to the upper limit of moth species present. After all, the DNR survey had documented 768 species in thirteen state parks. These parks range from the southeast corner of the state to the northeast corner. I am looking at only a tiny fraction of that territory. About 40 acres, to be exact.

My list surpasses the DNR’s list

Eventually, my species checklist surpassed the MN DNR survey’s list. After rechecking identifications, synonymy, and duplications, my list was at 865 species. That’s 97 species more than the DNR list. How to account for that?

Accounting for the differences

The differences in species counts are most likely due to our respective sampling methods and time available. The MN DNR survey’s list is almost entirely species from so-called macro-moth taxa. It is heavily weighted towards Geometridae and Noctuidae.

It is likely that the smaller moths, the so-called micro-moths, were not within the scope of the survey. It would have taken too much time to identify every moth. This would delay the report and critical action on Lymantria dispar dispar expansion into Minnesota.

So, while our lists overlap for most of the macros, my list also includes micro-moths. These include those from the superfamilies Gelechioidea, Nepticuloidea, Tineoidea, Tortricidae, and other taxa with mostly minute moths.

When I am mothing, I try to photograph and later identify every moth that comes to my moth light. I am not under any time constraints to complete fieldwork or produce a final report. Some unidentified moths have sat in my photo files for years before I figure them out. They needed to present the bigger picture. I am just filling in the details and have plenty of time to do it.

My checklist will continue to grow

I’ve been working on documenting the moths on my land for eight years. I don’t think I am done yet. I also don’t think annual additions to my checklist have peaked.

The rate of new species additions has been about 33 per year since 2020. As of 2025, the species checklist stands at 865 moth species with 34 new additions. This includes macros and micros. If that rate continues, the checklist will reach 1,000 species in about four years.

Mothing into the fall and even the winter

Autumn is upon us now. Soon, almost all insect life outdoors will be gone. In the meantime, I will continue to photograph right up until the snow falls and the lakes freeze. But even in winter, it is possible to find some insect life, including moths, outdoors.

*Operophtera bruceata* (hunter’s moth) flies in late October. It continues into November when night temperatures typically drop into the 30s and upper 20s.

Ctenucha virginica: a day-flying moth, wasp mimic, and wetland inhabitant

**Female *Ctenucha virginica* resting on a foundation during the day.**

The blue wasp moth, Ctenucha virginica, is another moth in the Arctiinae (Tiger and Lichen Moths), like the woolly bear or Isabella moth. And like the woolly bear moth, its fuzzy larvae also overwinter, feeding briefly in the spring before pupating. They just don’t get as much attention as the woolly bears do.

*Ctenucha virginica* showing the metallic blue abdomen. The feathery antennae indicate this is a male. The long projections on the antennae help it to detect pheromones that the females are giving off.

Description

The descriptions below are based on my observations of this moth.

The adult Ctenucha virginica moths are large (wingspan 38 to 52 mm) with dark black (brown in older individuals as scales wear off) forewings fringed with white patches and darker black patches near the base and angle. The underwings are black and fringed in white. The abdomen and thorax are metallic blue, and the head is bright orange with black eyes. The antennae and legs are black. The antennae of males are fringed and comb-like.

The metallic blue color of the thorax and abdomen and the orange head of Ctenucha virginica mimics some species of blue wasps and so may serve to deter predators.

The larvae are are black and covered by tufts of short, yellow and white hairs. There is a white line along the sides under the fuzz. The fuzzy hairs of some individuals may be white. The legs are pink, which helps to distinguish white forms from similar-looking fuzzy white caterpillars.

When and where to see the larvae

Spring is the best time to find blue wasp moth caterpillars when they have emerged from hibernation and are feeding. In some years, they can be quite abundant. I have observed the larvae feeding on grasses, sedges, and iris in the spring. The preferred larval habitat is graminoid-rich wetlands, but I’ve also seen them in old hayfields, especially in damp areas.

Once, I found a Ctenucha virginica caterpillar feeding on frost lichens (Physconia sp.) growing on a black ash tree. It had climbed about 6 feet up the tree to get to this lichen. Below the tree grew the caterpillar’s usual food plants: iris, manna grass, and Carex species.

*Ctenucha virginica* larva on sedge in a vernal pool. The pink legs and the white stripe are visible.

Living in wetlands is not without dangers. In the spring, they may flood, and the caterpillars could drown. Their fuzzy hairs do help them to float, but eventually, these become waterlogged. One spring during flood season, as I was walking through a flooded sedge marsh, I found several dozen Ctenucha virginica caterpillars floating in the water. I collected each one and moved them to some sedge tussocks that stood above the water. I hope that helped them out.

A *Ctenucha virginica* caterpillar in a vernal pool. It is early spring (March 28, 2019), and some patches of ice are still present. The caterpillar seems unfazed by this. I moved it to drier ground anyway.

Pollinators

Ctenucha virginica moths are pollinators. Disguised in their wasp-like coloration, they fly during the day, nectaring at many kinds of flowers in upland and wetland sites.

***Ctenucha virginica* on *Rudbeckia hirta***

They also drink dew from plant leaves. The one pictured below was drinking dew droplets from the leaves of American hazel (Corylus americana). American hazel is covered in sticky red glandular hairs, and I wonder if this, in addition to water, was what it was seeking. Perhaps there are chemicals in the glandular hairs it needs.

*Ctenucha virginica* is drinking dew from the glandular hair-covered surface of American hazel leaves. The filiform antennae show that this is a female.

Active at night, too

Ctenucha virginica moths are frequent visitors to my moth lights. Last year, in late June and early July, they were in abundance, with ten or more each night. In the photos below are a few of the visitors I saw last summer.

More caterpillars this spring?

With so many Ctenucha virginica moths last summer I expect there will be an abundance of their caterpillars this coming spring. If there are then I will collect some so I can let them pupate in a safe environment and learn a little more about that stage of their life cycle.

Insects That Mimic Stinging Wasps: A Look at Synanthedon acerni

In a previous post, I wrote about syrphid flies that mimic bees and wasps. But are there other insects with this mimicry superpower? The answer is yes. Other types of flies, beetles, and moths all have species that mimic stinging insects. The moth Superfamily Cossoidea (Carpenter and Clearwing Moths) is notable for the many species that mimic stinging wasps.

Synanthedon acerni (Family Sesiidae, Subfamily Sesiinae, Tribe Synanthedonini) is one such very wasp-like moth. Its wasp-like appearance allows it to be active during the day while it visits flowers, feeding on nectar.

Life history

The larvae of Synanthedon acerni are not quite as benign. Known as the maple callus borer moth, its larvae bore into the trunks of maple (Acer spp.) trees. Eggs are laid near wounds in the bark. Entry into the tree is through these wounds on the tree’s trunk. The larvae bore into the bark and then into the cambium, where they feed on the inner bark and sapwood. Feeding takes place during the summer within galleries. In the winter, they hibernate in the galleries and resume feeding in the spring.

At maturity, the larva constructs an oblong cocoon of wood fragments, frass, and silk within the gallery, close to the surface, covered by a thin escape window. When ready to emerge, the pupa cuts open the cocoon and the escape window. The fully formed Synanthedon acerni moth then exits the pupa, which is left partially stuck in the gallery.

The same tree may be used year after year, weakening it and eventually leading to its demise. A callus will form on the trunk after repeated infestations.

Two Spectacular Tiger Moths: Arctia caja and Arctia parthenos

Arctia caja, great tiger moth, and Arctia parthenos, St. Lawrence tiger moth, are moths in the Family Erebidae, subfamily Arctiinae, which includes these previously discussed moths: Lophocampa maculata, Halysidota tessellaris, Pyrrharctia isabella, Apantesis williamsii, Apantesis virgo, Apantesis phalerata, and Haploa contigua.

Arctia caja and Arctia parthenos are strikingly beautiful moths, as showy as any butterfly, which are just day-flying moths anyway.

Description

Arctia caja is a large moth with a wingspan of 27-32 mm. The forewings are brightly colored in white and brown, forming a mosaic pattern. The underwings are orange-red and marked with large, round to slightly irregular black discal, basal, and submarginal spots containing metallic blue scales. The abdomen is orange-red but darker than the underwings. (Sources: Moths of North Carolina, Pacific Northwest Moths, BugGuide)

Arctia parthenos is also a large moth with a wingspan of 28-33 mm. Its forewings are chocolate brown, marked with numerous pale yellow or cream-colored spots. The underwing is orange with irregular black markings. The abdomen is dark brown to black with orange sides and tip. (Sources: Moths of North Carolina, Pacific Northwest Moths, BugGuide)

Habitat

Arctia caja occurs in northern hardwood forests, conifer forests, wet meadows along creeks and rivers, in disturbed agricultural areas, gardens, and in urban areas. (Sources: Moths of North Carolina, Pacific Northwest Moths, BugGuide)

Arctia parthenos also occurs in northern hardwood forests, conifer forests, boreal mixed woods and parklands, moist shrubby arctic tundra, and mountains in the south. (Sources: Moths of North Carolina, Pacific Northwest Moths, BugGuide)

Host Plants

Arctia caja is polyphagous and feeds on many kinds of herbaceous plants as well as some hardwoods. (Sources: Moths of North Carolina, Pacific Northwest Moths, BugGuide)

Arctia parthenos is also polyphagous but has a preference for hardwoods such as willow, aspen, and alder. (Sources: Moths of North Carolina, Pacific Northwest Moths, BugGuide)