The browntail moth has been getting a lot of attention because their numbers have spiked to a level we haven’t seen in quite some time.
Why do we care so much? Because the toxic hairs shed by browntail moth caterpillars can cause a severe rash or respiratory issues for those who encounter them. These hairs are easily encountered once they become airborne. Many people don’t even know they are being exposed because the hairs are so small.
2021 Maine Update
During their 2021 winter web survey, the Department of Forestry spotted webs in every county in Maine. Below are the counties with the highest increase and highest infestation. View the Maine DACF full 2021 survey.
Counties with Highest Increase in Infestation
Counties with Highest Infestation
The weather plays a huge part in hair activity. Dry and windy weather sets the hairs in motion. For March and April, the average wind speed has been 3.5 mph with an average maximum of 20 mph (higher than average) and the average rainfall in March and April was 1.9″ (lower than average). If that continues into May and June, it means this could be a bad BTM season. The current drought monitor indicates we are “abnormally dry.” The NOAA May- July forecast indicates an “equal chance of above normal, near-normal, and below normal” precipitation levels. I’m going to guess that means we’ll be around the middle.
The previous year also plays a role. In particularly wet springs, a fungus can develop which kills the caterpillars. This means they will not turn into moths and lay lots of eggs for hatching the following year. That is substantial since each moth lays 25-400 eggs. That didn’t happen in 2020. Maine had its 18th driest June since 1895 and May was also below average.
The Cause of the Health Issues
Throughout much of their life cycle, the moth sheds its toxic hairs which become airborne or attach to leaves and brush. When the barbed hairs contact our skin or lungs, they can cause itchy painful rashes or respiratory issues. Issues are reported most in June and July when the toxin concentration in mature larvae is at its highest.
The most common reaction occurs when the caterpillar hairs contact the skin. This can cause both chemical reactions to the toxins and physical irritation when the hairs get embedded in the skin. The chemical reaction, referred to as dermatitis, produces a severe rash similar to poison ivy. Symptoms include itchy, blistered and swelled skin. The rash itself is not contagious. It’s caused by a reaction to the toxins that are in the hairs. Unlike the oil of the poison ivy plant, the hairs are not likely transferred to others through physical contact.
Respiratory issues are less common but can be particularly problematic for asthmatics. If you have asthma, you should carry your inhaler with you when spending time outside, especially during windy conditions. If you choose to be outside under these conditions, you may want to wear a mask that covers your nose and mouth.
If the hairs get caught in the mucosal areas of the mouth or throat they can cause burning, irritation or itchiness. Symptoms may be relieved by taking liquid Benadryl which helps counter the histamine reaction that the hairs can cause. However, you are encouraged to seek medical attention.
Symptoms can appear within hours of contact. If you think you’ve developed a reaction, make an appointment with your doctor as soon as possible to discuss treatment options.
There is no antidote for the toxins, so treatment is focused on relieving symptoms and eliminating further exposure. Coastal provides a compounded topical browntail moth medication which has been shown to significantly reduce discomfort from the rash. The compound is available, by prescription only, in both lotion or spray form. The spray is especially beneficial in treating these types of rashes because they are painful to touch. For those who have an acute case, a short course of oral corticosteroids may be prescribed.
Since many reactions occur over weekends, seeing a doctor may not be immediately possible. In these cases, you may find relief by soaking in a warm bath and applying calamine lotion or antihistamine cream.
You can also make an over-the-counter version of our prescription-strength lotion. Combine equal parts of the following OTC creams: hydrocortisone 1% (e.g. Cortizone 10), diphenhydramine hydrochloride 2% and zinc acetate 0.1% (e.g. Extra Strength Benadryl), benzocaine 20% (e.g. Lanacane), and pramoxine hydrochloride 1% (e.g. Itch-X). Although not as strong as our compounded lotion, it may provide some relief.
There are several actions you can take to reduce your risks.
- Avoid places that appear to be infested. Indicators include vacated nests and trees and shrubs with a lot of missing leaves.
- Wear a respirator, protective eyewear, and cover exposed areas of skin. This is important on windy days or when performing activities that would stir up hairs such as lawnmowing or raking.
- Wipe or rinse off lawn furniture before sitting in them.
- Take precautions when driving through infested areas in an open-air vehicle.
- Do yard work on damp days or spray the area your working in. Moisture will help keep the hairs from becoming airborne.
- Blow window fans outward instead of inward. You may not get the benefit of the breeze, but it will pull hot air out and will prevent pulling hairs in from outside.
- Don’t dry laundry outside. Hairs can become embedded in clothes and cause reactions when you wear them.
- Wash clothes after spending time in an infested area to remove embedded hairs.
- Take a cool shower after spending time in an infested area.
- Use duct tape to remove any hairs that may have embedded while outside.
- Remove nests. This should only be done in winter or early spring, while the larvae are dormant. Many nests are too high for the average person to remove, so check with an arborist to see if they offer nest removal service. View a list of licensed arborists willing to prune winter nests or a list of licensed pesticide applicators willing to treat browntail moth.
2020 Exposure Risk Map from the Maine Forest Service
Click the image below to view the full map on the Maine Forest Service’s website. Watch the MFS website for the 2021 map.
How do you know they’re in the area?
The area of infestation has previously been in the southern coastal part of the state, however, the area of infestation continues to grow. View the Maine Forest Service’s risk map for the latest status (the map for 2021 should be out soon).
Their nests are noticeable webs that are typically found in oak or apple trees. They appear in the fall and shelter the larvae through winter. In spring, hundreds of larvae can emerge from each nest to start wreaking havoc on trees and humans.
The best indicators of browntail moth infestation are vacated nests and trees and shrubs with a lot of missing leaves.
Resources and More Information
- Lessons Learned from Browntail Moth Seasons
We’ve seen a lot of patients suffering from the rash. In this article, we share what we’ve learned.
- Frequently Ask Questions from the Maine Forest Service
This is a really good resource for questions you have about controlling the population, avoiding the rash, etc.
- Maine Forest Service
The site contains a lot of information including a risk map and a list of arborists willing to prune browntail webs.
- 2021 Browntail Moth Winter Web Moth Survey
- Maine CDC Division of Disease Surveillance
Information on the rash and how to submit areas as a public health nuisance.
- Midcoast Browntail Moth Support Facebook Page
Updates on the situation as they get them.
- Browntail Moth Research Report from U-Maine
- 2021 Falmouth Browntail Moth Updates
Includes spraying information and a list of roads to be treated.
- Yarmouth Browntail Moth Updates
Includes information on the treatments and a list of arborists in Cumberland County who will prune webs and apply pesticide treatments.
- State of Maine Browntail Moth Control Statutes
Includes information on declaring a public health nuisance and aerial spraying rules.
- Harpswell study finds surprising browntail moth survival Forecaster article summarizing a study funded by the town of Harpswell.
- Browntail Moth Field Research and Trials
Harpswell Heritage Land Trust
- Bills that have gone through the State Legislature: