Maine’s outdoor enthusiasts face an unexpected health threat that many discover too late—caterpillars that can cause painful, poison ivy-like rashes and serious respiratory problems.
With browntail moth caterpillars alone affecting all 16 Maine counties and being declared a public health nuisance by the Maine CDC, understanding these rash-causing species has become essential for anyone spending time outdoors in the Pine Tree State.
The microscopic, barbed hairs shed by certain caterpillars can become airborne and cause skin reactions ranging from mild irritation to severe, weeks-long rashes requiring medical attention.
Even more concerning, inhaling these toxic hairs can trigger respiratory distress, particularly dangerous for individuals with asthma or other breathing conditions.
This guide will help you identify the six most problematic caterpillar species in Maine, understand the health risks they pose, and learn proven strategies to protect yourself and your family.
From recognizing the distinctive features of each species to implementing effective prevention measures, you’ll gain the knowledge needed to enjoy Maine’s outdoors safely while avoiding painful encounters with these deceptively dangerous creatures.
Caterpillars in Maine That Cause Rashes
1. Browntail Moth Caterpillar
The browntail moth caterpillar (Euproctis chrysorrhoea) represents Maine’s most serious caterpillar health threat. These invasive pests have dark brown bodies with a broken white stripe running along each side and two distinctive red-orange spots on their backs near the tail end. The caterpillars reach about 1.5 inches in length and are covered in thousands of microscopic, barbed hairs that contain potent toxins.
Important Note: The Maine Center for Disease Control and Prevention has officially declared browntail moths a public health nuisance due to their widespread impact on human health.
The toxic hairs cause dermatitis similar to poison ivy, but the effects can be far more severe and long-lasting. Most people develop localized rashes lasting hours to days, but sensitive individuals may experience severe reactions persisting for weeks. The barbed hairs become embedded in skin, causing both chemical reactions from toxins and physical irritation.
Browntail moth caterpillars are active from April through late June, feeding primarily on oak, apple, cherry, and other broadleaf trees. They create distinctive silky webs at branch tips during winter, which serve as overwintering shelters for hundreds of larvae.
Key Insight: The toxic hairs remain dangerous for up to three years after being shed, continuing to pose health risks long after the caterpillars have pupated or died.
These caterpillars pose unique dangers because their hairs easily become airborne through wind, mowing, raking, or any activity that disturbs vegetation. Even driving through infested areas with windows down can expose sensitive individuals to harmful hairs.
2. Hickory Tussock Moth Caterpillar
Hickory tussock moth caterpillars (Lophocampa caryae) are easily recognizable by their striking white fuzzy appearance punctuated by distinctive black hair pencils. These caterpillars feature dense white hairs covering their bodies with prominent black tufts projecting from their heads and tails, creating an almost decorative appearance that can be deceptively appealing to children.
The prickly hairs serve as an effective defense mechanism and can cause itchy, irritating rashes upon contact. While not as severe as browntail moth reactions, hickory tussock caterpillar stings can still produce uncomfortable skin irritation lasting several hours to days.
Common Mistake: Children are particularly vulnerable to hickory tussock caterpillar exposure due to their natural curiosity and tendency to handle interesting-looking creatures they encounter outdoors.
These caterpillars primarily feed on hickory, walnut, and other nut-bearing trees, becoming most noticeable in late summer and early fall when they leave host trees to search for pupation sites. During this wandering phase, they’re commonly found on sidewalks, driveways, and outdoor furniture.
The caterpillars grow up to 1.5 inches long and are most active during daylight hours. Their distinctive appearance makes them relatively easy to identify, but their attractive fuzzy coat often tempts people, especially children, to touch them despite the potential consequences.
3. White-marked Tussock Moth Caterpillar
The white-marked tussock moth caterpillar (Orgyia leucostigma) displays one of the most elaborate appearances among Maine’s problematic caterpillars. These striking larvae feature bright yellow bodies with black markings, topped by distinctive white, black, and orange hair tufts that create an almost paintbrush-like appearance.
Four prominent white hair tufts emerge from the caterpillar’s back, complemented by two long black hair pencils at the head and one at the tail. Bright red spots dot the body, and orange spines project from various segments, creating a complex and visually impressive defensive display.
The irritating hairs can cause contact dermatitis similar to other tussock moths, though reactions are typically milder than browntail moth encounters. However, sensitive individuals may still experience significant discomfort and skin irritation requiring treatment.
Pro Tip: White-marked tussock caterpillars often feed on common landscape plants including roses, fruit trees, and shade trees, making encounters likely in residential areas.
These caterpillars feed on over 140 different plant species, including maple, oak, birch, apple, and many ornamental plants. Their broad diet and adaptability to urban environments make them common in parks, yards, and residential areas throughout Maine.
The species produces two generations per year in Maine, with caterpillars most abundant in late summer and early fall. Their striking appearance and tendency to feed on landscape plants increase the likelihood of human contact.
4. Gypsy Moth Caterpillar (Spongy Moth)
Gypsy moth caterpillars, now officially called spongy moth caterpillars (Lymantria dispar), pose both forest health and human health concerns in Maine. These caterpillars display distinctive paired blue and red spots along their backs, with blue spots near the head and red spots toward the tail, set against gray or brown bodies covered in long hairs.
The irritating hairs can cause skin reactions, though typically less severe than browntail moth encounters. However, spongy moth caterpillars can still trigger allergic reactions and skin irritation in sensitive individuals, particularly children who may handle them directly.
| Spongy Moth Identification | Details |
|---|---|
| Size | Up to 2.5 inches when mature |
| Distinctive Features | Paired blue and red spots |
| Body Color | Gray to brown with long hairs |
| Active Period | Late April through June |
| Preferred Hosts | Oak, birch, apple, willow |
These caterpillars are voracious defoliators, capable of stripping entire trees of leaves during outbreak years. While their primary concern involves forest and landscape damage, the health risks from their irritating hairs shouldn’t be overlooked.
Spongy moth populations follow natural cycles, with outbreak years occurring roughly every 7-10 years. During peak years, caterpillar abundance can create significant exposure risks for outdoor enthusiasts and workers.
The caterpillars prefer oak trees but will feed on over 300 different plant species when food becomes scarce. Their ability to defoliate large areas increases the likelihood of human encounters during peak population years.
5. Eastern Tent Caterpillar
Eastern tent caterpillars (Malacosoma americanum) create conspicuous silk tents in the crotches of tree branches, making them among the most visible caterpillar species in Maine. These caterpillars have dark bodies with blue sides and a white stripe running down their backs, distinguished from browntail moths by their lack of red spots and different tent construction.
The hairs covering these caterpillars can cause mild to moderate skin irritation in sensitive individuals. While reactions are generally less severe than browntail moth encounters, eastern tent caterpillars can still trigger allergic responses and skin discomfort requiring attention.
Important Note: Eastern tent caterpillars emerge from their tents to feed during the day, making encounters more likely for people working or playing near infested trees.
These social caterpillars feed primarily on wild cherry, apple, and other trees in the rose family. The distinctive silk tents serve as communal shelters where caterpillars rest between feeding periods and molt as they grow.
The species produces one generation per year, with caterpillars active from early spring through early summer. The conspicuous tents make infested trees easy to identify, allowing people to avoid areas with high caterpillar activity.
Eastern tent caterpillars rarely cause lasting damage to healthy trees, but their presence indicates potential exposure risks for humans. The caterpillars process in lines between tents and feeding areas, creating predictable movement patterns that can help people avoid contact.
6. Forest Tent Caterpillar
Forest tent caterpillars (Malacosoma disstria) differ from their eastern tent cousins by not constructing tents, instead feeding openly on tree foliage in large aggregations. These caterpillars display blue and black coloration with distinctive white keyhole-shaped spots running down their backs, making them identifiable when examined closely.
The irritating hairs can cause contact dermatitis, particularly when caterpillars are handled directly or when people work in heavily infested areas. During outbreak years, the sheer number of caterpillars increases exposure risks significantly.
Forest tent caterpillars prefer hardwood trees, especially oak, birch, maple, and aspen. They feed gregariously, often completely defoliating branches or entire trees during peak population years.
Key Insight: Forest tent caterpillar populations follow natural cycles with major outbreaks occurring every 10-15 years, followed by periods of low abundance due to natural predators and diseases.
These caterpillars move in distinctive processional lines between feeding and resting sites, sometimes covering sidewalks, roads, and outdoor surfaces. During peak years, their abundance can make avoiding contact challenging in heavily infested areas.
The species produces one generation per year, with caterpillars active from late spring through early summer. Their preference for feeding high in tree canopies sometimes reduces human contact, but fallen caterpillars and processing lines increase ground-level exposure risks.
Health Effects and Symptoms
Understanding the range of health effects caused by rash-inducing caterpillars helps individuals recognize exposure and seek appropriate treatment. Reactions vary significantly based on individual sensitivity, exposure duration, and the specific caterpillar species involved.
Skin Reactions:
- Immediate burning or stinging sensations upon contact
- Red, itchy rashes similar to poison ivy
- Raised welts or bumps at contact sites
- Blistering in severe cases
- Persistent itching lasting days to weeks
Respiratory Symptoms:
- Coughing and throat irritation from inhaled hairs
- Breathing difficulties, especially in asthmatics
- Chest tightness or wheezing
- Burning sensations in mouth and throat
- Swollen lymph nodes in severe cases
The microscopic hairs work through two mechanisms: chemical toxins that trigger inflammatory responses and physical irritation from barbed structures that embed in skin and mucous membranes. This dual action explains why reactions can be both immediate and prolonged.
Pro Tip: People with asthma or respiratory conditions should carry inhalers when spending time outdoors during peak caterpillar seasons and consider wearing masks in heavily infested areas.
Children typically experience more severe reactions than adults due to their sensitive skin and higher likelihood of direct contact with caterpillars. Parents should teach children to avoid touching any hairy or colorful caterpillars and to report encounters immediately.
Prevention and Protection Strategies
Effective protection from rash-causing caterpillars requires understanding their seasonal patterns and implementing multiple prevention strategies. The most successful approach combines awareness, avoidance, and protective measures.
Seasonal Timing:
- Peak risk period: April through July
- Browntail moths most active: May through June
- Tussock moths most visible: August through September
- Weather dependency: Dry, windy conditions increase airborne hair exposure
Protective Clothing and Equipment:
- Long-sleeved shirts and long pants when outdoors
- Closed-toe shoes and socks
- Gloves for any yard work or gardening
- Respirator masks in heavily infested areas
- Safety goggles when using power equipment
Environmental Modifications:
- Remove winter webs from trees during dormant season
- Keep grass cut short to reduce hiding places
- Dry laundry indoors during peak seasons
- Use damp conditions for outdoor activities when possible
- Avoid leaf blowing in infested areas
Activity Planning: Choose rainy or humid days for outdoor work, as moisture keeps toxic hairs from becoming airborne. Plan activities around weather conditions and avoid unnecessary exposure during peak caterpillar activity periods.
Common Mistake: Many people focus solely on avoiding live caterpillars but forget that shed hairs and old cocoons remain toxic and dangerous for years after the insects are gone.
Professional pest control may be necessary for severe infestations, particularly browntail moths on residential properties. Contact certified arborists or pest management professionals familiar with Maine’s caterpillar species for safe, effective treatment options.
Treatment and First Aid
Prompt treatment following caterpillar exposure can significantly reduce the severity and duration of symptoms. The key to effective treatment involves quickly removing toxic hairs and managing inflammatory responses.
Immediate Response Steps:
- Remove clothing carefully – shake out garments outdoors before bringing them inside
- Use tape to lift hairs – gently dab the sticky side of duct tape on affected skin to remove embedded hairs
- Take a cool shower – use soap to wash away remaining hairs; avoid hot water which can worsen reactions
- Apply ice packs – reduce swelling and provide immediate relief from burning sensations
- Avoid scratching – prevents secondary infections and further skin damage
Topical Treatments:
- Hydrocortisone cream with aloe for anti-inflammatory effects
- Antihistamine creams to reduce itching and swelling
- Calamine lotion for drying effects on blistered areas
- Cool compresses using witch hazel for immediate relief
Oral Medications:
- Over-the-counter antihistamines like Benadryl or Claritin
- Ibuprofen or acetaminophen for pain and inflammation
- Prescription corticosteroids for severe reactions
Homemade Treatment Compound: Maine General Medical Center recommends mixing:
- 1/4 cup witch hazel
- 1/2 tube hydrocortisone cream
- 1/2 tube diphenhydramine cream
- 1/4 tube Aspercreme or lidocaine cream
Important Note: Never use topical and oral diphenhydramine simultaneously, as the combination can cause excessive drowsiness and other complications.
When to Seek Medical Attention
While most caterpillar exposures can be managed at home, certain symptoms require immediate medical evaluation. Understanding warning signs helps prevent complications and ensures appropriate treatment for severe reactions.
Seek Emergency Care For:
- Difficulty breathing or wheezing
- Swelling of face, lips, or tongue
- Widespread rash covering large body areas
- Signs of secondary bacterial infection
- Fever or systemic illness
Schedule Doctor Visit For:
- Rashes persisting longer than a week
- Increasing pain or swelling after initial treatment
- Pus or drainage from affected areas
- Reactions not responding to over-the-counter treatments
Special Considerations: People with asthma, allergies, or compromised immune systems should consult healthcare providers promptly after exposure. Children may require medical evaluation sooner than adults due to their increased sensitivity and potential for more severe reactions.
Document exposure details including the caterpillar species (if known), exposure duration, and initial symptoms to help healthcare providers determine appropriate treatment approaches.
Frequently Asked Questions
Q: Can you get a rash from caterpillars without touching them directly? A: Yes, the toxic hairs from browntail moths and other species can become airborne and cause reactions even without direct contact. Wind, lawn mowing, and other activities can disperse these hairs widely.
Q: How long do caterpillar hairs remain dangerous in the environment? A: Browntail moth hairs can remain toxic for up to three years, while other species’ hairs typically lose potency within one year. The hairs gradually wash into soil but can resurface during dry, windy conditions.
Q: Are some people more susceptible to caterpillar rashes than others? A: Yes, sensitivity varies greatly among individuals. Children, people with allergies or asthma, and those with sensitive skin typically experience more severe reactions.
Q: What’s the best time of year to remove browntail moth webs? A: Winter is the safest time to remove webs when caterpillars are dormant and weather conditions keep toxic hairs from becoming airborne. February through March is considered optimal timing.
Q: Can pets be affected by these caterpillars? A: Yes, dogs and cats can experience skin irritation and respiratory problems from exposure to toxic caterpillar hairs. Keep pets indoors during peak activity periods in heavily infested areas.
Staying Safe in Maine’s Outdoors
Living and recreating safely in Maine requires awareness of these six rash-causing caterpillar species and their seasonal patterns. By learning to identify browntail moths, tussock moths, and tent caterpillars, you can make informed decisions about outdoor activities and protection strategies.
The key to avoiding painful encounters lies in understanding that these creatures pose health risks beyond their immediate presence. Toxic hairs persist in the environment long after caterpillars have moved on, making year-round caution necessary in areas with known infestations.
Remember that Maine’s natural beauty can be enjoyed safely with proper preparation and awareness. Check local forest service reports for current infestation levels, plan outdoor activities during low-risk periods when possible, and always have treatment supplies readily available.
This information is for educational purposes only and is not intended as medical advice. Always consult with a qualified healthcare professional for persistent symptoms or severe reactions to caterpillar exposure.
