Hickory Tussock Moth Caterpillar

Common Name

Hickory tussock moth

Scientific Name

Lophocampa caryae Harris, 1841
Order: Lepidoptera (butterflies and moths)
Family: Erebidae (tussock moths, tiger moths, and kin)

Summary

Hickory tussock moth caterpillars are fuzzy, white, and black caterpillars that are often very apparent in the fall, sometimes in large numbers. The hairs may irritate the skin of people sensitive to them, but there are no known cases of systemic allergic reactions in response to the hairs of this species.

Distribution

Hickory tussock moths are found primarily in northeastern North America from Maine and New Brunswick south to North Carolina, west to Wisconsin and Illinois. They also occur southwest into Texas and Mexico, but are less common in that region.

Description

Young caterpillars are white with black spots (Figure 1). Older caterpillars can grow up to 1.7 inches (4.5 cm) and are covered in white and black setae or hairs (Figures 2–4). The black setae are arranged in tufts along the back and a set of black "pencils" often occurs at the front and back. Their cocoons are spun from silk but incorporate setae for defense against predators (Figures 5–6). Adult moths are tan to light brown and have cream-colored spots that occur in rows; the underwings are cream colored (Figures 7–8).

Life History

Hickory tussock moths have one generation per year. Adult moths fly May–June and caterpillars are present July–September. Eggs are laid on the underside of leaves in clusters of up to 100 or more. The young larvae feed gregariously on one or a few closely associated leaves (Figure 2). Older larvae become more solitary and feed singly or in small groups. Populations occasionally break out and cause local defoliation. Mature caterpillars are often encountered when they leave the host plant and crawl around in search of a protected place to spin a cocoon (Figure 5). Adult moths are attracted to lights at night.

Host Plants

Hickory, walnuts, pecan, and American hornbeam are preferred hosts. Other hosts include ash, elm, oak, willow, and maple, but they can likely feed on most hardwood deciduous trees. Caterpillars have also been recorded on hops, Virginia creeper, raspberry, rose, sumac, and blueberry.

Medical Importance

Hickory tussock moth caterpillars use their hairs for defense – the hairs are barbed, easily detach, and can become embedded in the skin, eyes, or mucous membranes of potential predators. When they spin their cocoons, the caterpillars incorporate the hairs into the silk so that the cocoons are also protected (Figures 5–6).

Humans, especially young children, can be exposed to the hairs when the caterpillars or cocoons are accidentally or purposely handled, squashed, or ingested. One study from southwestern Pennsylvania found that children accounted for 80% of all exposures and that the majority of all exposures were dermal (on the skin).

While caterpillars are most often encountered during the fall, the cocoons may be found year-round; after the adult moths emerge in the spring, the cocoons remain behind and gradually deteriorate depending on how exposed they are, such that some may continue to be present throughout the summer. Hickory tussock moth caterpillars spin cocoons in protected places, so accidental exposures may occur when moving firewood or reaching into areas where the cocoons are not seen.

Exposure to hickory tussock moth caterpillar hairs generally results in a localized rash and associated itching. Ingestion of the hairs may additionally elicit associated drooling, irritability, and anorexia. Allergic reactions to the hairs have not been associated with hickory tussock moths; however, a 5-year-old boy suffered an allergic reaction after exposure to the related spotted tussock moth (Lophocampa maculata), so allergic reactions may be possible.

When caterpillars and cocoons are handled, the setae may become dislodged and lay upon the skin without embedding, in which case washing the affected area with water and soap should eliminate them without further issue.

If the setae become embedded in the skin, tape can be applied to the affected area to remove them. If tape is insufficient or some hairs remain embedded, they may need to be removed using fine forceps or tweezers. Antihistamines and topical steroids may be needed to treat localized itching and swelling.

If the hairs are ingested or embedded in the eye, or if an allergic reaction happens in response to the setae becoming embedded in the skin, immediate medical attention should be sought. While most patients need only minimal supportive care and recover spontaneously within 48 hours, care should be taken, given the potential risk of complications.

Control

Because hickory tussock moths are a native species, they are usually controlled by a host of natural enemies. When outbreaks do occur, the majority of defoliation occurs late in the season, just a few weeks before trees naturally drop their leaves, so the caterpillars do not generally cause long-term damage to the affected tree.

If control is warranted or desired, the best method will depend on the life stage of the caterpillars. If egg masses or aggregations of young caterpillars are discovered, the affected leaves or branches can be pruned out. The eggs/caterpillars can be moved to a different part of the property where their feeding can be better tolerated, or they can be killed by submerging them in a bucket of soapy water.

If many young caterpillars are found on smaller (generally <15 feet tall) trees, a product containing Bt (Bacillus thuringiensis) or spinosad can be applied. Both Bt and spinosad are organic insecticides that are derived from bacteria. Bt is very selective in what it affects (the subspecies Bt kurstaki affects only caterpillars), so it is safe to use around pollinators and other beneficial insects. Spinosad is somewhat less selective than Bt as it does not affect many beneficial insects but is toxic to many pollinators.

Older, larger caterpillars may be individually handpicked and killed in a bucket of soapy water (if hand picking, be sure to wear gloves). Bt and Spinosad become less effective as caterpillars grow, so if chemical control is desired, more broad-spectrum insecticides will need to be used. But again, by the time older caterpillars are present, it is unlikely that their feeding will damage the long-term health of the affected tree, so control is rarely warranted.

Warning

Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.

References

 DuGar, B., J. Sterbank, H. Tcheurekdjian, & R. Hostoffer. 2014. Beware of the caterpillar: Anaphylaxis to the spotted tussock moth caterpillar, Lophocampa maculata. Allergy & Rhinology, 5: e113–e115.

iNaturalist. 2019. Hickory tussock moth. Accessed 30 August 2019.

Kuspis, D. A., J. E. Rawlings, & E. P. Krenzelok. 2001. Human exposures to stinging caterpillar: Lophocampa caryae exposures. The American Journal of Emergency Medicine, 19(5): 396–398.

Lotts, Kelly and Thomas Naberhaus, coordinators. 2017. Butterflies and Moths of North America. Hickory tussock moth. Accessed 30 August 2019.

Robinson, G. S., P. R. Ackery, I. J. Kitching, G. W. Beccaloni & L. M. Hernández, 2010. HOSTS - A Database of the World's Lepidopteran Hostplants. Natural History Museum, London. Accessed 27 August 2019.

Tripi, P. A., R. Lee., J. B. Keiper, A. W. Jones, & J. E. Arnold. 2010. An unusual case of ingestion of a moth cocoon in a 14-month-old girl. America Journal of Otolaryngology, 31: 123–126.