May 2026 Installment
Taking the long view: a host from the coast
Often, it is necessary to take the long view about solving mysteries in nature…
In a swamp on the North Carolina coastal plain, tangled in greenbrier vines, twisted stems of Wax Myrtle (Morella cerifera) swirled into the steamy air. Standing knee deep in muck, I could see the trunks well and noticed a thin line winding its way down branches and even trunks—the tell-tale signs of a stem-mining moth in the genus Marmara. These mines were old and unoccupied but showed where a caterpillar had tunneled just under the surface of the trunk, creating a long squiggly line as it fed on its thin layer of bark.
Marmara mines on the trunk of Wax Myrtle (Morella cerifera)
Almost exactly four years ago, I was working on plant surveys along the coast for the State of North Carolina, when I found these mines on Wax Myrtle in a coastal swamp on the outer banks. I had found mines of many different species of Marmara moths before—their larvae often overwinter in the trunks, then finish feeding in the late winter or early spring. They make a semi-circular cut at the end of their mine, in a thin, flexible layer of bark near the surface (often on younger branches). Then they use silk to make that thin layer buckle, creating a pocket of air underneath called a bark flap (see photo below). Silk can do this because it shortens as it dries, so if they stick their silk to the bark surface, then as the silk shortens, this bends the bark flap. Larvae crawl into the bark flap and spin a cocoon, making strange tiny silk-wrapped spheres called “frothy bubbles” and fixing them on the outside of the cocoon (see photo below). No one knows what purpose these balls serve. Wagner et al. (2000) guessed that they protect the cocoons in some way from parasitoids that can eat insect prey from the inside out (after which their prey dies)—the bubbles create a physical barrier. When the cocoon is finished, the larva pupates inside the cocoon, and the adult emerges a couple of weeks later.
Bark flap on Wax Myrtle--you can see the semi-circular cut in the bark on the right, and the bulge or pocket where the cocoon might be in the center of the branch.
Marmara cocoon on Wax Myrtle. You can see the frothy bubbles on the white silk surface of the cocoon.
Mamara moths are sometimes leaf miners, often stem miners, and are sometimes both. Evidence suggests that many Marmara species are host-specific, meaning that many species probably feed on one or a few plant species only. Although it is necessary to raise an adult to identify species, they are often ridiculously difficult to raise to adulthood. This is because they are inside tree branches or trunks of only certain plants, and are at a stage when they can be collected for only a short time—they die if they are collected too early. Thus, raising adults requires that I find their cocoons. If they pupate in bark flaps, I can cut those bark flaps with cocoons inside them off of the branches with razor blades (see photo below—the bark flap came off of this one but had no cocoon in it yet). If they wander off of their host plants to spin cocoons, I would need to catch larvae before they exit the mines and hope they exit and spin cocoons in the container.
Bark flap cut from Wax Myrtle. The flap itself fell off, leaving the exposed bark below. There was no cocoon in the bark flap, so the larva was likely still in the layers underneath.
I figured I hadn’t much hope of raising the Marmara on Wax Myrtle from coastal plants. I don’t get to the coast very often, so it would be more of a gamble to find them at the right time. However, this coastal native plant has been introduced to, or has colonized, much of the Piedmont in North Carolina as well. In Raleigh and throughout the Piedmont, Wax Myrtle acts as an invasive species, moving into native habitats and taking up spaces that natives had filled previously. I found Wax Myrtles growing at Durant Nature Preserve along our lakes and was happy to find the Marmara mines on several of those plants. I have spent the last 2-3 winters observing these miners, and have found out that they do in fact make bark flaps (whew!). Through trial and error (mostly error), I was able to triangulate their pupation timing.
This year I was ecstatic that two 2-3 mm-long adults emerged from bark flaps I’d collected from Wax Myrtle trees (see photo below). Apparently, leaf-mining Marmara had been found on this host once in Texas, but no stem miners had been documented on this host before (Eiseman et al. 2017). With adults in hand, we now have hope of identifying the species or describing it if it is new. That may still take a while, as it involves dissection, comparison with other known species, writing, drawing, and everything that goes into publication. It still helps to take a long view. We may solve this mystery in the next few years. Other mysteries will take much longer to solve than this one.
Marmara adult, raised from Wax Myrtle--the moth is about 3 mm long.
References:
- Eiseman, C.S., Davis, D.R., Blyth, J.A., Wagner, D.L., Palmer, M.W., and Feldman, T.S. 2017. A new species of Marmara (Lepidoptera: Gracillariidae: Marmarinae), with an annotated list of known host plants for the genus. Zootaxa 4337 (2): 198-222.
- Wagner, D. L., Loose, J. L., Fitzgerald, T. D., DeBenedictis, J. A., and Davis, D. R. 2000. A hidden past: The hypermetamorphic development of Marmara arbutiella (Lepidoptera: Gracillariidae). Annals of the Entomological Society of America 93(1):59-64.