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)

Range

A neighborly moth

Genus overview

Haploa is a genus of moths in the superfamily Noctuoidea, family Erebidae, subfamily Arctiinae (Tiger and Lichen Moths). The genus comprises six species in North America north of Mexico and is not known from anywhere else. Four species are known from Minnesota: Haploa contigua, Haploa lecontei, Haploa reversa, and Haploa confusa.

So that’s the easy part. When I look over my photos of Haploa species, I am struck by the way Haploa lecontei, Haploa reversa, and Haploa confusa seem to grade into one another. Why? Maybe because I am misidentifying them. Or maybe because these are just photos of one species and its range of variation. Which species? I’m not sure anymore, but it might be Haploa confusa. The one I am sure of is Haploa contigua.

Haploa contigua

Haploa contigua is one of four species of Haploa with all white hindwings. The base color of the forewings is cream-colored to white. The costa and inner margins are bordered in dark brown. A diagonal dark brown line extends from the costa beyond the midpoint to the inner margin above the anal angle. Joining this is another line running from the outer margin. Haploa contigua lacks any lines or spurs in the antemedial portion of the forewing. All-white individuals are indistinguishable from other Haploa species with all-white forms.

Haploa contigua inhabits mesic woodlands to riparian woodlands. The larvae feed on the leaves of many species of woody and herbaceous plants.

The genus name “Haploa” is from the Greek word for “simplicity, singleness”, and the species epithet “contigua” is from the Latin word for “bordering” and so the neighbor moth.

I found some more leaf mines

**A leaf mine in a big-leaf aster leaf that was probably made by the larva of an *Ophiomyia* sp., a genus of leaf-mining flies.**

Recently, I’ve become more interested in leaf mining insects after finding what might be the serpentine leaf mine of a Stigmella moth in a blackberry leaf. This wasn’t the first moth leaf mine I have found. In 2017, I identified another leaf mining moth, Phyllocnistis populiella, recognizing it from its leaf mine in a balsam poplar leaf.

Later, in 2019, I found the adult of another poplar leaf mining species, Phyllonorycter nipigon. Beyond that, my findings of leaf miners have been sporadic and by chance when photographing micro-moths at my moth lights.

Changing weather, changing focus

With the colder fall weather, it is more difficult to find insects and other arthropods. So, now I am turning my attention to the signs of them.

Out on my walks in the woods late last month, I came across five more serpentine leaf mines. The first was in a big-leaf aster (Eurybia macrophylla), which is shown in the photo at the top of the page. The other four were in wild red columbine (Aquilegia canadensis), coltsfoot (Petasites palmatus), goldenrod (Solidago gigantea), and bunchberry (Cornus canadensis). I couldn’t find larvae in any of them, but I think I have a good idea of what made them.

**This leaf mine in a columbine leaf was probably made by a larva of *Phytomyza aquilegivora*.**

Possible identifications

The leaf mine in the aster leaf was probably made by the larva of a species of fly in the genus Ophiomyia, leaf mining flies in the family Agromyzidae.

**Phytomyza *agromyzina* in bunchberry**

While I’m not absolutely certain, the leaf mines in the other four plants were probably made by the larvae of leaf mining flies in the genus Phytomyza, also in the family Agromyzidae.

Columbine: Phytomyza aquilegivora
Bunchberry: Phytomyza agromyzina
Coltsfoot: Phytomyza albiceps group (see page 5)
Goldenrod: Phytomyza solidaginophaga

I’ve probably seen the adult Phytomyza flies, but didn’t give them a second thought, assuming they were just some more pesky flies buzzing around my head looking for blood or sweat. Next year, I’ll be paying more attention.

Leaf mining flies are species-rich

There are at least 600 named species of Phytomyza, making it the largest genus of leaf mining flies in the world. Ophiomyia has over 200 species. Species of Phytomyza and Ophiomyia are host-specific, which accounts for much of the diversity in their genera.

Cerodontha is another species-rich leaf mining fly genus in the Agromyzidae, with 285 species worldwide. Cerodontha is a monocot specialist mining the leaves of sedges (Cyperaceae), soft rushes (Juncaceae), irises (Iridaceae), and grasses (Poaceae). Some Cerodontha species have been found in Minnesota and neighboring Wisconsin.

A quick search of species of Phytomyza and Ophiomyia that might occur in northern Minnesota shows at least twenty species and five species, respectively. The number of Cerodontha species in Minnesota is unknown. I think next summer is going to be an interesting one.