Category: Lepidoptera

This autumn I was fortunate to have this really interesting experience with a common but fascinating moth species. I invite you to read about it and see the photography.

New documented host plant (Nymphaeaceae) and life history documentation for the highly polyphagous moth, Orgyia leucostigma (Lepidoptera: Erebidae), in eastern Missouri.

Orgyia leucostigma Smith, 1797 is a moth species in the family Erebidae that is found throughout eastern North America and is known to be extremely polyphagous. Commonly known as the white-marked tussock moth, O. leucostigma has been recorded using 166 plant species in 55 families as hosts, mostly consisting of deciduous plants, but coniferous and herbaceous plants have also been recorded (Robinson et al. 2023).

In early September 2024, I observed six mid- to late-instar larvae of O. leucostigma, each feeding on the leaves of Nymphaea odorata (Nymphaeaceae) that were growing in a small artificial “pond” in my St. Louis County, MO suburban yard. Unfortunately, these insects consumed every available leaf of N. odorata in the pond before they could pupate. The only other species in the pond available to them was the exotic Pontederia crassipes (water hyacinth), which they did not readily consume. I was able to locate and remove five final-instar larvae from the remnants of the original host leaves and placed them in an outdoor cage where they successfully switched to feeding on leaves of Quercus muehlenbergii and Q. imbricaria (both Fagaceae). Within seven days, all five larvae built cocoons to pupate within.

To my knowledge, this is the first documentation of a nymphaeaceous host plant for O. leucostigma, which expands the host range of this already highly polyphagous species by another family. Unfortunately, the caterpillars did not reach pupation feeding on N. odorata alone, so the ability of O. leucostigma to reach adulthood on this host cannot be confirmed yet. However, the fact that five larvae of O. leucostigma were able to reach the final larval instar feeding solely on N. odorata makes this highly likely.

Life history of Orgyia leucostigma
The lifecycle of O. leucostigma begins as an egg, typically laid in masses by the adult female. Eggs are laid in late summer or early fall on tree bark, branches, or other surfaces. A single female can lay anywhere between 100 to 600 eggs. These eggs are small, round, and white to pale yellow in color, and are coated in a protective frothy substance produced by the female to safeguard them from predators and environmental factors.

Lepidopterans use a variety of strategies in overwintering. In the case of O. leucostigma, the eggs remain dormant over the winter, entering a state of diapause, a period of suspended development that allows them to withstand harsh winter conditions. They hatch in the spring when the weather warms, typically around late April or early May, coinciding with the budding of trees that will serve as food for the larvae.

After hatching, the larvae emerge as small, hairy caterpillars. This larval stage is perhaps the most recognizable and distinctive phase of O. leucostigma. The caterpillars are known for their colorful and tufted appearance, with a series of tufts (or tussocks) of hair along their backs and two long black “pencils” of hair protruding from both the front and back ends. The body is primarily yellow or cream-colored, with a pattern of red and black markings.

As discussed above, the larvae feed on a wide variety of trees and shrubs, including both deciduous and coniferous species. In our area, oak, maple, and willow, are among the most common hosts. The larvae are voracious feeders and can cause significant defoliation when present in large numbers, which can lead to tree stress, although healthy trees typically recover without long-term damage.

Once the larva has reached its final instar, it will spin a cocoon in a sheltered location, often on the trunk or branches of trees, beneath loose bark, or on the sides of buildings. The cocoon is made from silk and incorporates most of the caterpillar’s own urticating body hairs, offering added protection from predators.

Inside the cocoon, the caterpillar transforms into a pupa, a resting stage during which the most dramatic metamorphosis occurs. The pupal stage typically lasts 10-14 days, during which time the organism undergoes a complete transformation from a larva into an adult moth.

Upon completion of the pupal stage, the adult moth emerges. The adult form of O. leucostigma exhibits strong sexual dimorphism. The males are small, grayish-brown moths with a wingspan of about 25-35 mm. They have feathered antennae that they use to detect pheromones released by females from a considerable distance.

In contrast, the females are wingless and remain on or near their cocoons after emerging. They are larger than the males and have a plump, cylindrical body covered with dense hairs. Since they are flightless, females rely on releasing pheromones to attract males for mating. After mating, the female lays eggs near the cocoon, starting the cycle again. The female typically dies shortly after laying her eggs, while the male lives a few days longer in search of other mates.

Due to the stationary habit of the females, it is fascinating that all dispersal is dependent on the larvae in this species. To do this efficiently, early-instar larvae will often “balloon,” letting out an amount of silk to catch the wind, thus allowing them to move to new areas much quicker than by crawling. This dispersal mechanism is also practiced by many spiders.

In this specific case, all five of the pupa that I reared produced female adults and each of these eclosed exactly 10 days after cocoons/pupa were formed. At dawn of each morning following the females emergence, I walked the outside perimeter of our screened porch wherein the screened moth enclosure was contained. Each morning I found up to six male adult O. leucostigma that I captured and placed in the enclosure containing the females.

Mating appeared to be very brief and within minutes of contact by a male, each female began ovipositing. It was quite shocking observing the differences in size of the females before and after their egg masses where completed. See photos below that I attempted to document these changes.

While observing and photographing these activities, I happened to notice that a jumping spider (F. Salticidae) was attacking one of the females prior to her ovipositing. The spider must have come from the oak branches that I placed in the enclosure to finish rearing the caterpillars. I took enough time to take a few photos of this and then removed the spider with a pair of forceps. I noticed a drop of hemolymph on the back of the female after removing the spider. However, the female did not seem too bothered by this and created her egg mass within a couple of hours of this incident.

Caterpillars of this species are often found during my caterpillar hunts. Sometimes they are so plentiful as to be annoying when hoping for rarer quarry. I had read about the stationary eggbound females of this species but had little hope of ever actually seeing one in person. I very much enjoyed documenting these activities and I will try my best at overwintering these egg masses to fruition.

Literature Cited

Robinson, G. S., P. R. Ackery, I. Kitching, G. W Beccaloni and L. M. Hernández (2023). HOSTS (from HOSTS – a Database of the World’s Lepidopteran Hostplants) [Data set resource]. Natural History Museum. Available from https://data.nhm.ac.uk/dataset/hosts/resource/877f387a-36a3-486c-a0c1-b8d5fb69f85a (last accessed 16 Sep 2024).