Parks commission: Spongy moth prevention starts at home

By Mary Jo Bertolino

You might not have heard of a spongy moth, but most likely you have had some kind of contact with them. Spongy moth is the new name for gypsy moth (Lymantria dispar). These moths were introduced to Massachusetts in 1869 by E.L. Trouvelot, an amateur entomologist hoping to start a silk business. They escaped his home and spread through the northeastern United States. 

The Department of Agriculture’s Animal and Health Inspection Services monitors the spread of the spongy moth and has counties that are currently quarantined for these invasive pests. The hope is that the spread can be contained to the current locations.

Unfortunately, Michigan is part of the area that the spongy moths have already taken hold. The damage from the larvae stage can decimate foliage on shade trees with oak, willow, apple, birch and beech trees being some of their favorite foods, although there are about 300 trees and shrubs that they will feed on. If the damage is early enough in the year, the tree may regrow some buds and leaves and should be able to recover from the infestation. If the infestation is large enough, the damage could be permanent and kill the tree. These damaged trees could recover in a year or two, so should not be considered dead until then.

Identifying the spongy moth

The first stage in a spongy moth’s lifecycle is the egg masses found on tree trunks, branches, and in protected areas outdoors. This can be outdoor furniture, children’s toys, play structures, vehicles, garbage cans and many other items left undisturbed outside. These masses are usually tan-yellow, fuzzy, usually 1 ½ inch long and ¾ inch wide but can be the size of a dime and can be found late fall, winter and early spring. The egg masses can contain 500-1,000 eggs.

When you find these masses, the easiest way to deal with them is to scrape them off their location and place the nest in a container of soapy water. Leave them in the container for 2 days before discarding them in the trash. Some suggest squashing the nests but squashed nests could leave some eggs to hatch in the spring. This stage is the longest in the life cycle and you will have the best chance of getting ahead of an infestation. You can also spray the masses with horticultural oil.

If you know that you have seen spongy moths on your property, look for the masses and remove them before they proceed to the next development stage.

The second stage is the larvae stage that erupts in spring, usually around mid-May. These larvae will be about 0.25 inch long and will climb up the tree to a branch then drop down on a silk strand to be blown by the wind to another location. This is called “ballooning” and if you have walked into a small wormlike insect hanging from a silk thread, you most likely walked into the nest area of the spongy moth. The larvae will continue to climb up to branches and do this again if the location isn’t suitable for its food consumption.  The area that these larvae travel is usually less than 100-150 yards from the original nest. The larvae will also leave a heavily infested tree in order to find a better feeding spot and can be blown by the wind up to a half mile.

Once the larvae start feeding, they go through stages of growth called “instars.” The males go through five stages of instars and the females go through six stages.

The female must gain energy to lay eggs and will be larger than the male at maturity. The first instar will last about a week, then they go through a molt.  The second instar will last another 5 to 8 days, then molt to become the third instar. They will continue this process until maturity and will continue feeding on the leaves of the tree that they call home.

The mature male caterpillars will be 1.5 to 2 inches long and the females will be 2.5 to 3 inches long. The red and blue dots on the backs of these caterpillars will become evident by the third instar. The young larvae feed during the day and the older larvae will feed at night. The older larvae will climb down the tree to escape their natural predators, birds, and hide in crevices and leaf litter for protection during the day. 

The best way to deal with the larvae stage is to stop it before it can get to the first instar. You can do this by using burlap folded in half and tied to the trees.  The opening of the burlap should be facing down. The larvae will get trapped in the fold and you can remove them to a bucket of soapy water.

Some people will use sticky tape to place around the trunk of a tree to capture the larvae. This can also be accomplished by putting a ring of duct tape around the tree with a sticky product on the tape such as Tanglefoot (composed of gum, resins, vegetable oil and wax), or turning your duct tape sticky side out.

Another method of stopping the larvae is using Bt (Bacillus thuringiensis) spray on the tree. This is only useful if the tree is short enough to spray.  Otherwise, you might want to contact an aerial company to do the spraying for you. Bt is a biologic product that is sprayed on the foliage and the larvae ingest it while eating the leaves. The efficacy of Bt on the larvae is 70 percent and will have to be resprayed after a rain. This biologic agent will kill the larvae but not harm humans or pets.

Bt is useful for all kinds of caterpillars and should be used judiciously. It can also kill butterfly larvae and should not be sprayed near milkweed and other plants that attract butterflies.

You may find larvae in an upside-down V shape on a tree. This is an indication of the nuclear polyhedriosis virus (Entomophaga) that has killed these larvae, usually ending a spongy moth outbreak. Fungal diseases will occur after a particularly rainy episode and will also interrupt the lifecycle of the larvae. Should you remove the carcasses? NO! The fungus is naturally occurring and will help to control future outbreaks. Outbreaks last from 2 to 4 years and afterwards the spongy moth population will remain low for some time.

The third stage of the spongy moth is the pupae stage. This stage lasts about 10 to 14 days and is easily identified by the hard brown cocoons. The male cocoon is smaller than the female and are found in crevices of bark or under branches but are not limited to those locations. They can be under picnic tables, outdoor items like dog houses, playhouses, planters, vehicle wheel wells and other protected locations. They can easily be removed and placed in soapy water for a few days or put in a plastic zipped bag to be discarded.  

The last stage of the spongy moth lifecycle is the adult winged moth. The female is easily identified by her white/beige wings and cannot fly. The female releases a pheromone to attract the male to her and after mating, she will release her mass of eggs and will die shortly afterward. The lifespan of this stage is about 2 weeks.

The male spongy moth is brown and grey in color and has feathery antennae to pick up the pheromone scent. They will fly back and forth in a zig zag pattern trying to locate a female. The adults do not feed during this time due to a lack of mouthparts. It would be difficult to try to locate the female before mating, but not impossible. Since they only live for 2 weeks at this stage, you would have better luck finding her egg mass.

Female spongy moths do not fly and if you see one flying, it must be reported to the federal or state agriculture officials. This will be one of the flighted spongy moth complex (FSMC) that is identical to the spongy moths that are already in Michigan. The only way to accurately know the difference is by DNA testing. If the FSMC were to be imported into the United States, it could be a major threat to our forests.

Proactive with landscaping

What do I do for my landscape?

Be proactive. Inspect your property for egg masses from October to May.  If you have the larvae that managed to get by your inspection, use a trap on your trees to capture them.

Found a cocoon? Place it in a bucket of soapy water or put it into a sealed container before discarding it.

For large infestations, you may need to get a professional to spray. The professionals book their services in the fall, so if you decide to call them, do it as soon as possible.

Invasive species cause harm to our natural environment, and everyone should do their best to eradicate them or report as necessary. Most invasives have been innocently brought in by someone who did not know the species was not native to the area. Diseases and insects cross state lines with firewood, maybe to an area that has no known predator or natural repellant. Do not take firewood from its local environment. Instead buy heat treated firewood if you must take it to your destination or use the local wood.

Inspect your RV and boat for insect nests and terrestrial species not native to your location. If your RV or boat has been standing in one place for a while, consider power washing it to remove unwanted travelers.

Together we can work to combat the invasives that harm our environment.

Mary Jo Bertolino is a member of the Laketown Township Parks and Recreation Commission.