The Very Hungry (LDD Moth) Caterpillar

If you have been outside recently exploring the trails in your area or just getting out in your yard, you have probably encountered numerous caterpillars and their handiwork. These are LDD caterpillars, also called gypsy moth caterpillars.

The LDD moth (whose acronym arises from its Latin name Lymantria dispar dispar) originates in Asia and Europe. It was introduced to North America in 1869 by a French scientist attempting to breed the LDD moth with silkworms. He was working in Massachusetts when one of the moths escaped, and quickly became an invasive species. The first report of LDD moth in Ontario was not until 1969.

The LDD moth is an invasive species that defoliates trees. It negatively impacts tree health and as a result, affects other species dependent on those trees. One LDD moth caterpillar can eat up to one square metre of leaves in its short lifetime. LDD moth prefers oak, maple, birch, white pine, and white spruce trees, but they will use about 300 different plant species as a host. Healthy trees can usually withstand LDD moth damage for a few years without serious impacts. However, when LDD moth are mixed with other stressors (e.g., drought, disease, other pests), the result can be reduced growth or even tree mortality.

Life Stages of the LDD Moth

The LDD moth goes through several life stages before actually reaching the adult moth stage.

1.   Egg Stage: The egg stage lasts from July to April. These masses of eggs occur on trees and other hard surfaces such as sheds, wood piles, and decks. The fuzzy light brown masses can contain 100 to 1000 eggs.

2.   Larval Stage: The larval stage begins in spring. In this stage, larvae hatch and begin eating foliage. In the beginning of this stage, larvae cannot be identified by their small black bodies. Nearing the end of this stage, larvae are much bigger and can be identified by their pattern of colours. They have five pairs of blue spots followed by six pairs of red spots on their backs.

3.   Pupa Stage: The pupa stage occurs from June to July. In this stage, the larvae shed their skin and their new skin hardens into a dark brown shell. After a week or two in the pupal shell, a larva will have transformed from a caterpillar to a winged adult moth.

4.   Adult Moth Stage: The adult moth stage lasts from July to August. Adult moths do not eat at all. Males are brown and can fly. The females are larger than the males, are cream coloured, and cannot fly. The males will live approximately one week, spending most of their time mating, and the females will die shortly after laying eggs.

LDD Moth in the Georgian Bay Biosphere

Despite being an invasive species, LDD moth is considered to have reached a state of naturalization and has periodic, predictable outbreaks. Luckily, LDD moth have a number of natural predators including a virus, a fungus, a small wasp which acts as a parasite, and other mammal and bird predators. An increase in the LDD moth population means there is more food available for its predators and after a lag of a few years, a subsequent increase in predator populations. More predators lead to a reduction in LDD moth density after 1-3 years. The cycle repeats every seven to ten years, and has kept the LDD moth population under control in past years. This does not mean, however, that LDD moths are not problematic. 

In the Parry Sound District, also called the French‐Severn Forest, 2,046 ha of defoliation was mapped in 2020 compared to 177 ha in 2019. The blue area on the map below represents defoliation in 2019. The red area represents defoliation in 2020. Much of the 2020 defoliated area was south of Parry Sound along the highway 400 corridor or near Georgian Bay. During ground surveys, defoliation and egg masses were observed in Port Carling, Lake Muskoka, Tobin Island, Lake Rosseau, and Go Home Lake.

Did you know?

A common question about LDD moth larvae is whether they bite. LDD moth larvae do not bite, rather, they have little hairs called setae, which create a stinging sensation on the skin. The larvae use their setae as a defence mechanism against predators. Contact with larvae may cause rashes consisting of red and white bumps which are itchy and uncomfortable. The rash typically appears in 8-12 hours and is resolved within a few days to two weeks. The best ways to prevent contact with the larvae are to avoid picking them up and to wear long pants and sleeves when around trees in the spring.

Found LDD Moth on Your Property? Here’s What You Can Do!

If you have found LDD moth in the egg, larval, or pupa stage, there are several control methods you can use. The infographic below provides a summary of which techniques work best at different stages and times of year.

In early spring you can scrape the egg masses off trees into soapy water. This will effectively kill the eggs. The caterpillars, pupae, and moths can also be killed later in the year in soapy water. To make collecting the caterpillars easier, try the burlap method. The burlap method involves wrapping and securing burlap around a tree trunk and folding it over. When it becomes too sunny, the caterpillars will climb between the layers of burlap for shade. Once they are gathered in one spot, it is easier to scrape many caterpillars into soapy water at one time. Repeat this process daily. See the video below for a tutorial.

The biological pesticide Btk (Bacillus thuringiensis kurstaki) is a naturally occurring bacteria that can be applied to foliage when the larvae are hatching and beginning to feed. When the caterpillars ingest Btk, it kills them. Btk can be dangerous to other species when used incorrectly. Before considering applying Btk on your property, be sure to do your research. For more information on Btk and safe Btk practices, read Health Canada’s Btk fact sheet

Be sure to report your LDD moth sightings using the EDDMapS Ontario app, the EDDMapS Ontario website, or by calling the toll-free Invading Species Hotline at 1-800-563-7711.

Further Reading:

LDD Moth in the Georgian Bay Biosphere information package

Ontario Invading Species Awareness Program – LDD Moth

Ontario Ministry of Natural Resources and Forestry – LDD Moth

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