The stinging nettle caterpillar, the larval stage of a non-native species of moth previously named the oriental moth, is a striking insect. Caterpillars are brightly colored with conspicuous markings, warning other organisms that the caterpillars also possess well developed urticating spines found on fleshy horns. Caution: the spines of these caterpillars can cause a reaction similar to touching stinging nettle plants. They should not be handled. Caterpillars, once mature, spin hard cocoons often found in the forks of smaller twigs of their host plants. Cocoons may look like buds on the plant or bark and blend in and are white and gray-brown in color. It is thought that the cocoons of this species were accidentally introduced into a suburb of Boston, MA around 1906. The pupal stage is the overwintering stage, with adult moths emerging in the spring. Fernald reported adult moths emerging in Massachusetts in late June, early July. Adults are active for a short period, and do not feed. Female moths lay their elliptical, flattened, and transparent eggs singly on the undersides of host plant leaves. Caterpillars feed on the leaf undersides initially, but eventually eat the entire leaf, except for the midrib and main veins, from the tip as they grow in size. Eight instars of caterpillars have been observed for this insect (Dyar, 1909). Larvae have been reported in Massachusetts from late July to October, pupae from May to June, and adults from late June to early August (Schaffner, 1959).
The stinging nettle caterpillar is a very obscure insect that is rarely seen in a limited portion of eastern Massachusetts. Caterpillars may feed on the foliage of many hardwoods but mostly Norway maple, sycamore, apple, and hawthorn. More recently it has been confined to about a 30-mile radius around Boston, Massachusetts and has not been seen until limited reports of finding the caterpillars have been made in recent years (Topsfield, MA, 2019; The Caterpillar Lab). The largest extent of the distribution of this insect around Boston may have been in 1942 when an approximately 300 square mile radius was reported (Dowden, 1946). At this time, it is still helpful to report the stinging nettle caterpillar to the MA Department of Agricultural Resources (MDAR), here: https://massnrc.org/pests/report.aspx . Take a photo of any caterpillars seen, and collect a specimen if it can be safely done. MDAR or UMass Extension can assist in submitting a sample for confirmation to the USDA Animal and Plant Health Inspection Service (APHIS).
A sex pheromone of this species has been isolated previously by scientists (Shibasaki et al., 2013), although populations of this insect are thought to be so low currently in Massachusetts that monitoring for this insect with traps may not be necessary.
Handling the caterpillars of this species in any way (such as to collect and destroy them) is not recommended. Larvae can be a nuisance, because their spines cause a nettle-like irritation when they come in contact with exposed skin. Because of the very low population of this insect, cultural management is likely unnecessary.
An important parasitoid wasp of the stinging nettle caterpillar is Chrysis shanghaiensis, which may parasitize 1/10 of the pupae in the native range of this insect. In 1917 and 1918 this parasitoid wasp was brought to and released in Massachusetts from China, and by 1919 only 6% of the cocoons were found to be parasitized (Fernald, 1920). Additionally in North America, the following parasitoids (some thought to be species complexes) have also been noted from oriental moth: Trichogramma minutum, Ascogaster quadridentata, Chaetexorista javana, and Lixophaga mediocris (Gates et al., 2012). There is question as to whether or not populations of these natural enemies or biocontrols still exist in Massachusetts or North America, because the population of oriental moth is so low. Additional natural enemies or biological control agents of the oriental moth were reported by Schaffner in 1959. These include the dipterans Chaetexorista javana and Compsilura concinnata as well as the hymenopteran Psycophagus omnivorus. Chaetexorista javana was brought intentionally from Japan in 1929 and 1930 and approximately 85,000 adult flies were released in the Boston area with first recoveries of the species in 1930 following the initial releases (Schaffner, 1959).
Abamectin (NL)
Acephate (larvae) (NL)
Azadirachtin (NL)
Bifenthrin (larvae) (NL)
Chlorantraniliprole (larvae) (NL)
Indoxacarb (larvae) (L)
Neem oil (NL)
Spinosad (NL)
Tebufenozide (larvae) (NL)
Chemical management of this insect is more than likely unnecessary because populations are so low, they cause no measurable damage to their hosts.
Active ingredients that may be applied systemically include: abamectin (injection), acephate (injection), azadirachtin (injection, soil drench), chlorantraniliprole (soil drench), and neem oil (soil drench).
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.
