Last year, my wife and I were mesmerized by a blooming carpet of marvelous mallow (Malvaceae) in Magee Marsh just east of Toledo. We couldn’t identify exactly which mallow was blooming, and I couldn’t get close enough to see a host-specific pest, so I had nothing. As a botanist, I’m a pretty good entomologist.
Using her smartphone, my wife found that the dominant mallow in Magee Marsh is Swamp Rose-Mallow (Hibiscus moscheutos, syn. H. palustris). I tried to contribute to the identification effort using my own smartphone, but only one of is, so I got nothing.
The scientific name applied to the swamp rose-mallow in Magee Marsh was correct up until mid-December 2025. That’s when Hanes and Barrett published a plant taxonomy paper descriptively titled, “The Hardy Hibiscus – Still Hardy, but No Longer Hibiscus …” (see Selected References). The authors reported that based on phylogenetic data, some members of the genus Hibiscus were moved out of that genus and into a reinstated genus, Muenchhusia. Thus, H. moscheutos is now M. moscheutos (basionym Hibiscus moscheutos). Taxonomists never sleep.
M. moscheutos is native to Ohio and ranges across eastern North America from southern Ontario to Florida. Consequently, it has gathered many common names including Common Rose Mallow, Crimson-Eyed Rose-Mallow, Eastern Rose-Mallow, Hardy Hibiscus, and Wild Cotton, to name a few.
The “hardy hibiscus” common name may be obsolete, but it references a key trait; plants are hardy in our temperate winters. Personally, I like the common name “Swamp Rose-Mallow.” It’s not glamorous, but it references the preferred habitat, flowers, and mallow family.
Two weeks ago, I saw a beautiful bloom display at Bowyer Farm, Warren County, OH, and recognized the plants as looking similar to those in Magee Marsh. The 600+ acre farm is owned by the Cincinnati Zoo and Botanical Garden (CZBG) and includes a native plant program, wetland restoration, and a browse program to feed animals in the Zoo.
This time, I could get close to the blooming plants. Based on the flowers, seed pods, leaves, and location (Ohio), I’m confident in declaring that the plant providing the wonderful floral display was swamp rose-mallow. Also, I emailed Brian Jorge, Manager of the Native Plant Program, CZBG, for help because I was confidently uncertain about my ID.
I visit Bowyer Farm frequently; however, this was the first time I had observed such a heavy bloom by swamp rose-mallow. Brian noted that each year, they harvest the seed and distribute it anywhere there are openings in their wetlands. Their successful efforts visually demonstrate the value of using this attractive native plant where drainage is poor.
Brian also noted that another closely related species, M. laevis (basionym H. laevis), is growing on the farm. The plant was once classified as H. militaris, and there is a connection between the specific epithet and common names that include “halberd,” such as Halberdleaf Hibiscus, Halberd-Leaved Rose-Mallow, and Halberdleaf Rosemallow. The leaves of halberdleaf rosemallow resemble the pointy end of a “halberd,” a medieval military (= militaris) weapon.
Sawfly Wreckage
I went searching for halberdleaf rosemallow to take photographs. However, instead of finding a mallow with halberd-like leaves, I found halberdleaf rosemallow with see-through leaves.
The plants were being wrecked by the so-called Hibiscus Sawfly (Atomacera decepta, family Argidae) larvae. Obviously, the sawfly didn’t get the memo about the hibiscus name-change. However, since "hibiscus sawfly" is not a common name approved by the Entomological Society of America (ESA), there remains the opportunity to give it a more accurate name.
Indeed, the sawfly is also called the Mallow Sawfly, which is far more accurate. The literature notes that it may be found on several members of the mallow family, including hollyhock (Alcea spp.). However, it should not be mistaken for the Hollyhock Sawfly (Neoptilia malvacearum), or vice versa.
As shown in the images illustrating this Alert, mallow sawfly larvae feed on the lower leaf surface, and their cryptic coloration makes them difficult to spot. They range in color from translucent early instars to later instars tinted various shades of semi-translucent green.
All instars have transverse bands of short, black bristles. While taking pictures, I noticed droplets of liquid oozing from the tips of the bristles. According to the literature, the bristles are attached to glands that exude toxic peptides that function as feeding deterrents primarily targeting ants. I tried to minimize disturbing the larvae; however, it’s likely the oozing defense chemicals were in response to me (Ant Man?).
Early instars consume the lower epidermis and mesophyll, leaving the upper epidermis intact. Later instars devour all leaf tissue except the veins, eventually giving the affected leaves a lacy appearance.
Females are black with a distinct orange spot on top of their thorax. Males are entirely black. The females use their saw-like ovipositor (= sawfly) to insert individual eggs into leaves.
There are multiple overlapping generations per season, as illustrated in my images showing females ovipositing at the same time multiple instars are feeding. Thus, this sawfly can rapidly cause see-through leaves to appear on entire halberdleaf rosemallow plants.
Host with the Most
I observed a significant difference in the mallow sawfly’s host preference on Bowyer Farm. Despite being in close proximity, as shown in the image below, Halberdleaf rosemallow was extensively damaged while swamp rose-mallow remained largely untouched.
The difference in host preference was dramatic, even where leaves of the two mallow’s overlapped. My observations do not agree with those reported by others; however, there may be a possible explanation found in the literature.
Boyd and Cheatham (2004) evaluated 12 genotypes of Muenchhusia (basionym Hibiscus) for resistance to the mallow sawfly. They found that both swamp rose-mallow (M. moscheutos) and halberdleaf rosemallow (M. laevis) were at the high end of the sawfly damage spectrum, indicating both are highly susceptible.
Barrios (2019) worked entirely with swamp rose-mallow hybrids by crossing chemically induced tetraploids with natural diploid forms. She found that the hybrids with the greatest amount of hairs (pubescent = tomentose) on the leaves had less feeding damage from the mallow sawfly compared to those without hairs (glabrous).
If you look closely at the image below, you’ll see that the underside of the swamp rose-mallow leaf collected on Bowyer Farm is covered in a dense layer of tiny, woolly hairs. The underside of the highly pubescent leaf shimmered in the sunlight. It wasn’t as dramatic as the leaf pubescence responsible for silver linden’s (Tilia tomentosa) common name, but it affected my photography!
The image below shows mallow sawfly larvae on the underside of a halberdleaf rosemallow leaf. It also clearly shows that the leaf is glabrous.
Of course, the observations presented in this Alert are purely anecdotal. As noted above, the mallow sawfly has multiple generations per season, and there’s plenty of growing season left. I’m going to monitor the site. It may turn out that once the sawfly finishes eating all the halberdleaf rosemallow leaves, its second helping will be swamp rose-mallow leaves.
Selected References
Barrios, K. M. (2019). Tools for ornamental breeding: intraspecific crossing, triploid development, insect resistance evaluation, inheritance testing, somatic embryogenesis, plant growth regulators, and physical mutagenesis with Hibiscus spp., Liquidambar formosana 'Formosan Gold,’ Helianthus simulans, and Illicium parviflorum [Doctoral dissertation, University of Georgia]. University Libraries, University of Georgia, UGA Open Scholar.
https://openscholar.uga.edu/record/21441?v=pdf
Boevé, J. L. (2021). Behavior and body size modulate the defense of toxin-containing sawfly larvae against ants. Scientific Reports, 11(1), 13610.
https://www.nature.com/articles/s41598-021-93074-2.pdf
Boyd Jr, D. W., & Cheatham, C. L. (2004). Evaluation of twelve genotypes of Hibiscus for resistance to hibiscus sawfly, Atomacera decepta Rohwer (Hymenoptera: Argidae). Journal of Environmental Horticulture, 22(3), 170-172.
https://www.ars.usda.gov/ARSUserFiles/60620000/BoydPDF/jeh22%283%29170-172.pdf
Fay, M. F. (n.d.). APG - classification by Consensus. Kew. 7 Minute Read. Retrieved August 7, 2026, from https://www.kew.org/read-and-watch/apg-classification-consensus
Hanes, M. M., & Barrett, R. L. (2025). The Hardy Hibiscus – Still Hardy, but No Longer Hibiscus: Reinstatement of Muenchhusia (Malvaceae: Hibisceae). Journal of the Botanical Research Institute of Texas, 19(4), 375.
https://journals.brit.org/jbrit/article/view/1437/1471
Petre, C. A., Detrain, C., & Boevé, J. L. (2007). Anti-predator defense mechanisms in sawfly larvae of Arge (Hymenoptera, Argidae). Journal of insect physiology, 53(7), 668-675.
https://doi.org/10.1016/j.jinsphys.2007.04.007
Savolainen, V., & Chase, M. W. (2003). A decade of progress in plant molecular phylogenetics. TRENDS in Genetics, 19(12), 717-724.
