National Moth Week takes place July 21st through the 27th, which presents the perfect opportunity to talk about one of our state’s invasive species, the spongy (gypsy) moth. Since 1869, the spongy moth has been a pest to over 300 varieties of trees across the United States. From their caterpillar stage to adulthood, these moths spread fast and cause a lot of damage. Let’s take a look at what makes them so dangerous to North Carolina’s forest land and how you can help prevent their spread across the state.
History of the spongy (gypsy) moth
The spongy moth, formerly known as the gypsy moth and originally from Europe, was introduced to the United States in 1869 by Etienne Leopold Trouvelot. As an amateur entomologist, Trouvelot attempted to interbreed the gypsy moth with native caterpillars, his goal being to establish a strong and prosperous silkworm industry. After a huge storm hit and overturned the caterpillar enclosures in his backyard, the spongy moth that we know today was unintentionally released and has been making its way across the United States ever since.
The spongy moth did not find its way into North Carolina until 1971, when a total of 13 moths were caught in North Carolina in various locations across the state. Since then, it has been found in various counties across our state. Although it continues to be a dangerous pest to North Carolina trees, the treatment and programs in use today are among the most successful invasive pest management programs to date.
Lifecycle of the spongy moth
Like many other insects, the spongy moth has a four-stage lifecycle: egg, caterpillar, pupae, and adult. In the spring, the caterpillars hatch and begin their spread. A female moth can lay anywhere from 300 to 1,000 eggs, so these caterpillars arrive in mass. Typically, caterpillars will remain on the egg mass until a warm day approaches and then take residence in a nearby tree and begin eating. The caterpillar stage of the spongy moth is actually the most dangerous because each individual insect can eat up to 11 square feet in their lifetime. With hundreds of caterpillars hatching out of each egg mass, this can lead to defoliated trees very quickly! They feed on the leaves of over 300 varieties of trees, but especially love oak trees, as well as other hardwood species found in North Carlina.
The spongy moth caterpillars go through multiple growing stages before moving on to the pupae stage. The growth of the caterpillar is categorized by this molting process, where is sheds its exoskeleton to grow larger. For male caterpillars, this process happens five times before moving on to the next life stage. For females, the molting process will happen six times. Depending on the temperature, each molting season lasts approximately two weeks. Throughout this time period, the caterpillar continues to feed on the foliage of trees around it, causing even more damage and stress to the trees.
After their final molting stage, the spongy moth caterpillars transition into the pupae stage where they enclose themselves in a hard, brown shell-like pupal casing. The female pupae are often larger than the male pupae. Typically, the pupae will stay encased for about three weeks, depending on how warm it has been, before emerging as a fully grown adult moth.
After this time period, the spongy moth splits its pupal casing and emerges as a fully formed female or male spongy moth. The male moths emerge several days before the female moths, but once they emerge their sole purpose is to reproduce. The adult spongy moths do not feed. In fact, female spongy moths don’t even fly. Once they emerge, the female spongy moth will stay near where she emerged and begin emitting pheromones to attract the male moths. The male moths will fly around, typically about four or five feet above the ground, searching for the female moths to reproduce. With only a two-week lifespan, both the female and male moths die off shortly after reproducing.
Identifying the spongy moth
Currently, there are only two counties in North Carolina that are under quarantine for spongy moth infestations, Currituck County and Dare County, however, all 100 North Carolina counties are at risk for a new spongy moth infestation. So how can you identify the spongy moth and keep an eye out for it in your area? There are three traits that distinguish the spongy moth from other moths in our state that pose similarities. The caterpillar is the easiest to distinguish, while the pupae and adults are easiest to confuse with other moth species.
- Egg Mass Color and Size: The egg masses laid by adult female spongy moths are tan and buff in color, hairy, and typically the size of a quarter. Oval in shape, these egg masses can often be found in sheltered places, like the underside of a tree limb, but they can also be laid anywhere the female moth can crawl to, including lawn ornaments, play equipment, or car wheels. Female moths will lay their eggs in the summer each year.
- Spongy moth caterpillars: The caterpillars are often very easy to spot because of their bright color patterns. Throughout the molting stage, caterpillars can grow from 1/16 inches in length to 2.5 inches. After hatching, caterpillars will display a bright yellow head, five pairs of blue dots, and six pairs of red dots on their backs. In addition to their bright colors, these caterpillars are very hairy. They can be found crawling and feeding from March to late May.
- Male spongy moth characteristics: Unlike many other moth species, male spongy moths fly during the daytime. Male moths will typically stay toward the inside edge of the forest and fly about four to five feet above the ground. The easiest way to identify them, however, is their antennae, which are very large and feathery.
If you sight a spongy moth, caterpillar, or egg mass, please contact our Plant Industry Division directly at (919) 707-3730 or send an image to badbug@ncagr.gov.
Why is the Spongy Moth considered an invasive species?
To be considered an invasive species, a species must not be native to the environment it is in, spread easily from where it first arrived, and be able to harm the environment, economy, or human health. Since each spongy moth caterpillar can eat 11 square feet of leaves in their lifetime, an infestation of this pest causes healthy trees to be stripped of their leaves multiple years in a row, which can lead to tree death
With spongy moth caterpillars feeding on over 300 varieties of trees across North America, and female moths laying anywhere from 300 to 1,000 eggs at a time, the trees across our state are in danger of being attacked by spongy moth at an alarming rate. This is why staff in our Plant Industry Division work hard every day to both trap and treat the insects to control their spread across the state and decrease the population.
Trapping and Treatment of the Spongy Moth
Our Plant Industry Division works to control the spongy moth population in North Carolina through two methods: trapping and treatment. Each year between April and June, staff members set out roughly 16,000 traps across our state. These traps are monitored from July to September to determine location of spongy moths in our state and which counties, if any, need to be placed under quarantine. Learn more on that at: https://ncagr.gov/plant-industry-spongy-moth-regulations.
So what are traps made from? Most traps used by our Plant Industry Division are known as “delta traps,” which is an orange or tan coated paper triangular box with pheromone lure and adhesive. The string lure in the trap is doused in the female spongy moth’s sex pheromone to attract the males. Once the males land inside the trap, they are trapped in the adhesive. In areas where there are higher numbers of spongy moths, milk carton shaped traps are used because they can hold more moths. These traps also contain the female sex pheromone. If you see a trap of any kind in your area, please do not disturb or move it!
In areas where high numbers of spongy moths have been found, our Plant Industry staff uses the SPLAT, or Specialized Pheromone & Lure Application Technology, mating disruption method to treat and control the population. This treatment is completely organic, and is the safest method for our staff to use for both the moths and the surrounding community. The female sex pheromone is released by plane over the infestation area. This stops the spongy moths from being able to find one another to reproduce. None of the moths are hurt or killed in the process, simply disoriented. “It’s much like spraying strong-scented body spray in a room full of blindfolded people and asking them to find who’s wearing it,” said Sara Lalk, Forest Health Research Operations Manager with our Plant Industry Division. “It’s hard to figure out where the scent’s coming from!” These treatments are not only the safest to use in our state, but also incredibly effective.
How can you help?
“Help us help you,” Sara Lalk said. “A lot of the people who are doing these treatments and putting out traps are more than happy to talk with you and answer any questions that you might have. Engage with us and allow us to ease your mind about the process. We care about the trees in our state just as much as you do, and at the end of the day, we all want the same goal – healthy forests and beautiful land.”
Here are a few other ways that you can help control the spread of spongy moths in your area:
- Don’t move firewood. Buy it where you burn it.
- Check your clothing and suitcases when travelling and camping
- Keep an eye out for moths, caterpillars and egg masses in trees near your home or forests in your area
- Meet with Plant Industry staff in your area to learn more about what they are doing and how you can get involved
We are so thankful to have our Plant Industry staff on board to help protect forests in our state by managing these pests. Thank you for helping them do their job by identifying and reporting the spongy moth when you see one. Together, we can control and eliminate the dangers of this pest across our state.
