The European Gypsy Moth (Lymantria dispar dispar) is a species of moth introduced to North America in the 1860s and has since become one of the most notorious pest species in the deciduous forests of Northeastern North America. Unfortunately, the species finally made its way as far West as my home state of Michigan, USA during the late 1980s and has since firmly established themselves in the forests across the whole of the state.
Map of United States Gypsy Moth Establishment
Gypsy Moth larvae are both voracious eaters and quick to spread to new territory. Thanks to their light weight and the fine hairs that line the segments of their bodies, Gypsy Moth caterpillars are capable of being blown into the air and carried by strong winds. To held facilitate this spread, the caterpillars will climb nearby vegetation and then hang from silken threads that they spin until a strong breeze passes by. This airborne dispersion combination with the spread caused by the transport of firewood containing Gypsy Moth egg masses allows unchecked populations to travel as much as 13 miles per year. While this may seem like a small distance for any given year, changing climates and a lack of effective means for controlling their spread leave a relatively high likelihood that the species will ultimately spread across virtually all deciduous forest environments in the continental United States within the next 50 years.
Probability Map for Predicted United States Gypsy Moth Establishment
This is a pest species of major concern in North America because the larvae are one of the primarily causes of defoliation in the deciduous forests of Northeastern America. While the larvae tend to prefer oak, aspen, and fruit tree species, over 300 tree and shrub species are host to this pest, leading to widespread defoliation following their mass emergence in the Spring. Young larvae are black with long, hair-like setae, while their more mature counterparts are adorned with 5 pairs of blue spots and 6 pairs of red spots along the length of their bodies. Freshly hatched larvae are only around 3 mm in length, whereas a full grown caterpillar may reach up to 90 mm before entering the pupal stage.
Young Gypsy Moth Instars (1-2 molts) [May 29, 2021 - Kent Co., Michigan, USA]:
Mature Gypsy Moth Instars (4-6 molts) [June 13, 2021 - Kent Co., Michigan, USA]:
The spread of Gypsy Moths is particularly concerning because they are so efficient at defoliating vegetation, particularly in years with large outbreaks. The first major outbreak in the United States is dated to 1889 in the greater Boston area, where records reflect an outbreak that left local trees completely defoliated and caterpillars covering virtually all sidewalks and homes across 30 suburban towns. Despite enacting pest control strategies ranging from the application of acid to egg masses, burning infected trees, and the application of insecticide agents, efforts to control the species were largely ineffective, allowing the pest to then spread progressively further westward.
It is at this point in the year that many of the mature Gypsy Moth larvae will being to enter the pupal stage, where they will remain for a following 14–17 days before emerging as adult Gypsy Moths. In their adult form, Gypsy Moths are sexually dimorphic, with the males taking on a more buff tan and brown coloration, while the females are bright white with light brown banding and spots. The adult moths will live for about 1 month, where their only further goal being to find a mate and pass on their genetic information. The moths possess no operating digestive system at this stage and do not feed. After successfully mating, the female will lay around 500 eggs in a mass that is then covered by a fuzz-like mat to protect and insulate the eggs until they hatch the following year. This fuzzy mass can cause a rash similar in appearance to those produced by poison ivy if touched with unexposed skin. Touching live larvae results in a similar rash as well, further adding to the nuisance factor of the species.
Male Gypsy Moth:
Source: https://en.wikipedia.org/wiki/Lymantria_dispar_dispar#Introduction_to_North_America
Female Gypsy Moth:
Source: https://en.wikipedia.org/wiki/Lymantria_dispar_dispar#Introduction_to_North_America
Gypsy Moth Egg Mass:
Source:https://bygl.osu.edu/node/859
While efforts continue to try to slow the spread of this pest species, the population continues to expand its range in the United States. Since Gypsy Moths tend to lay their eggs on dead wood, the transport of infected firewood has become a primary means by which the species is able to infect new regions. Because of this, many state and national agriculture authorities encourage individuals to not transport their own processed firewood from one location to another. In my home state of Michigan, two firewood producers, Michigan Fuelwood Products and Beaver Creek Wood Products, are under contract with the state government to provide USDA-certified, heat-treated wood to state campgrounds and parks so that infect logs are not transported to these locations.
Though the species will likely one day become endemic to much of the continental United States, preventative measures such as these aim to both slow the spread of the pest as well as stifle yearly population numbers that threaten mass defoliation event like those first witnessed in 1869. For my part, I choose to step on each and every Gypsy Moth caterpillar I find (after getting a photo that is). They are not welcome in my forest.
References:
https://reliantmedicalgroup.org/blog/2017/05/31/gypsy-moth-rash-need-know/
https://en.wikipedia.org/wiki/Lymantria_dispar_dispar#Introduction_to_North_America
https://naldc.nal.usda.gov/catalog/CAT82474520
https://www.aphis.usda.gov/aphis/resources/pests-diseases/hungry-pests/the-threat/hp-egm/hp-egm
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