Caution: hairs found on the caterpillar and pupal life stages of this insect can cause a rash similar to poison ivy. Some individuals are very sensitive to browntail moth hairs and may also experience allergic reaction. The chance of interacting with browntail moth hairs increases between May and July, although they could be a problem at any time of year.
The larval or caterpillar stage of this insect is present from August until the following June (spending the winter in webs they create on the tips of host plant twigs). In the fall, groups of caterpillars are found creating webs around a tightly wrapped leaf (covered in bright white silk) where they will overwinter in groups of 25-400. These 2-4 inch long webs can be found on the ends of branches often on apple or red oak. As soon as leaves begin to open in the spring (usually by April), the caterpillars will crawl from their webs to feed on the new leaves. Caterpillars are fully grown around June and spin cocoons in which they pupate. These cocoons are also full of the irritating hairs and should be dealt with extreme caution. Adult moths emerge in July and females lay eggs on the undersides of leaves in masses of 200-400, covering them with hairs from their bodies. (Adults do not typically cause skin rashes.) Eggs hatch around August and September and larvae feed shortly before forming their overwintering webs.
The primary concern with this insect are the poisonous hairs found on the caterpillars. Contact with the caterpillar or its hairs can cause a rash similar to poison ivy in susceptible individuals. If hairs break off and blow around in the wind, they can cause difficulty breathing and headaches. While this insect can act as a defoliator in the larval stage, feeding on the leaves of many deciduous trees and shrubs, this activity may be secondary to concerns about public health risks. Care should be taken to avoid places infested with these caterpillars, exposed skin or clothing should be washed, and the appropriate PPE should be worn if working with these insects. Consult your physician if you have a reaction to the browntail moth.
Monitoring for this insect can be helpful in the fall, approximately in September, but also before leaves open in the spring in areas, such as parts of Cape Cod, where this insect has been seen in previous years. At those times, it is possible to scout for the tightly wrapped webs which have overwintering caterpillars within by looking at the tips of host plant branches. If interacting with either the larval (caterpillar) or pupal life stages of this insect, it is important to wear personal protective equipment such as gloves, long sleeved shirts and pants, and close-toed shoes. Professionals who know they are allergic to browntail moth should avoid working with this species.
If the overwintering webs are found, they may be carefully clipped from the host plant and submerged in soapy water or destroyed before host plant leaves become available and the caterpillars begin to feed and develop. Take care to avoid contact with the hairs of this insect when handling any life stages or otherwise working in areas where they may be found.
An interesting piece to the history of the browntail moth in North America includes its association with Compsilura concinnata, a parasitoid fly that was originally introduced as a biological control organism for spongy moth (Lymantria dispar). While this fly alone was not able to reduce spongy moth populations, it appears that it did decimate browntail moth populations. Although Compsilura concinnata had a positive effect in reducing browntail moth populations, it is also a generalist which attacks over 180 species of native Lepidopterans in North America.
Until recently, a suite of natural enemies and biological control organisms have kept browntail moth populations low in much of its former introduced range in North America. Parts of southern coastal Maine have been dealing with outbreak populations of browntail moth since roughly 2016. In Massachusetts, in recent years, browntail moth has been confined to coastal parts of the state in certain areas of Cape Cod and the North Shore, particularly on beach plum. However, it is a good idea to be aware of this insect and know how to identify it properly.
At least two tachinid fly parasitoids are known to attack browntail moth: Compsilura concinnata, as previously mentioned, and a species of Townsendiellmyia. Various wasp parasitoids will also attack browntail moth, including those in the genera Pimpla, Brachymeria, and others. An entomopathogenic fungus (Entomophaga aulicae; a different species than E. maimaiga, which attacks Lymantria dispar caterpillars) as well as an NPV virus (the Euproctis chrysorrhoea Nucleopolyhedrosis Virus; EcNPV) also impact browntail moth populations.
Acephate (NL)
Acetamiprid (L)
Azadirachtin (NL)
Bacillus thuringiensis subsp. kurstaki (NL)
Beauveria bassiana (NL)
Bifenthrin (NL)
Carbaryl (L)
Chlorantraniliprole (NL)
Chlorpyrifos (N)
Cyantraniliprole (NL)
Diflubenzuron (N)
Flonicamid+cyclaniliprole (N)
Horticultural oil (L)
Indoxacarb (L)
Malathion (L)
Methoxyfenozide (NL)
Neem oil (NL)
Pyrethrins+piperonyl butoxide (L)
Pyrethrin+sulfur (NL)
Spinosad (NL)
Tebufenozide (NL)
Primarily found in older apple orchards and on beach plum in coastal areas. Also on several different deciduous hosts, including but not limited to those listed above.
Active ingredients that may be applied systemically include: abamectin (injection), acephate (injection), acetamiprid (L), chlorantraniliprole (soil drench), cyantraniliprole (soil drench, soil injection), and neem oil (soil drench).
When used in nurseries, chlorpyrifos is for quarantine use only.
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022 neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
