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Lambdina fiscellaria and Lambdina athasaria

Eastern hemlock looper caterpillar. Photo: Pennsylvania Department of Conservation and Natural Resources - Forestry , Bugwood.
Scientific Name: 
Lambdina fiscellaria and Lambdina athasaria
Common Name: 
Hemlock Looper
Growing Degree Days (GDD's): 
120–707 GDD's (Source: Robert Childs, UMass Extension), 448-707 GDD's (Source: Cornell Cooperative Extension) Base 50F, March 1st Start Date.
Host Plant(s) Common Name (Scientific Name): 
Arborvitae (Thuja spp.)
Balsam fir (Abies balsamea) *Preferred host.
Hemlock (Tsuga spp.) *Preferred host.
Larch (Larix spp.)
Spruce (Picea spp.)
White spruce (Picea glauca)
Insect Description: 

Two species of geometrid (inchworm; looper) caterpillars are collectively referred to as the hemlock looper. Lambdina fiscellaria and L. athasaria are common native defoliators of hemlock that are found in Canada and the United States. (Additional subspecies may also occur.) Both may be found in mixed populations on their hosts. They are most significant as pests of hemlock and balsam fir, but have also been reported from larch, spruce, and arborvitae. Hemlock loopers have a black band with white teardrop-shaped spots along the length of the body. Tiny eggs (1 mm.) overwinter and hatch in late May or early June, and the young larvae begin to feed on the foliage of their host plants. Young larvae prefer new foliage, however as they age they will feed on old needles from other conifers. (Additional deciduous hosts have also been reported, such as sugar maple and white birch.) Hemlock loopers are described as wasteful feeders, not consuming the entire needle. Larvae grow slowly, and complete their maturation by late August or early September. Four or five instars are reported, depending upon the location. Mature hemlock loopers are approximately 1.18 inches in length. Caterpillars drop to the ground to pupate by late July. Pupae are generally brown and green with dark spots and not found within a cocoon. Adults emerge by September and October. Moths are small (approx. 1.25 inch wingspan) and tan to gray/brown in color. When populations are high, large numbers of these moths may be found mating and resting at the base of trees or surrounding vegetation. Eggs are laid singly on the bark of the trunks and limbs of trees at that time (Johnson and Lyon, 1991). Historically, populations may be heavy for 2 to 3 years, then virtually disappear (Robert Childs, Personal Communication). Outbreaks may be difficult to predict. (The University of Maine Cooperative Extension provides great information about historical outbreaks of these insects in Maine and Newfoundland.)

Damage to Host: 

Larvae are very wasteful feeders, feeding on and killing many needles. Needles will brown as a result of being fed upon, and by the middle of the summer the outer shoots and twigs may be barren of needles. In high populations, complete defoliation is possible. The "nipping" or "notching" behavior of this insect may lead to fallen needles forming a mat beneath the tree. Silk strands may be found in trees following pupation of hemlock loopers as the caterpillars use the silk to drop to the ground. Trees have been killed by these insects when in an outbreak, particularly hemlock (after a single year of defoliation) and fir (after one or two years of defoliation). Deciduous trees are rarely killed by these species.


By late May and early June, monitor for inchworm-like caterpillars in hemlock and balsam fir. Branches of preferred hosts can be shaken over a light colored sheet or umbrella (held upside down under the branches) weekly from June 1st to July 1st to look for fallen caterpillars. Search for notched needles. As the summer progresses, look for browning needles or branches and clipped needles beneath trees. Silk may be seen in trees in July as pupation occurs. Pupae may be found in the cracks and crevices of the base of the tree or debris found nearby on the ground after the end of July.

Cultural Management: 

No significant cultural or mechanical management options are noted.

Natural Enemies & Biological Control: 

Many records of natural enemies of hemlock loopers are known to science. Extensive lists of parasites of the eggs (Telenomus and Trichogramma spp.), larvae (Actia interrupta and Blondelia eufitchiae), and pupae (Pimpla and Pteromalus spp.) are available. Pathogens (Cordyceps militarisEntomophaga aulicaeEntomophthora shpaerosperma, and granulosis virus) of the larvae are also recorded. Predators (Calosoma sycophanta) of the caterpillars also exist. Some examples are found here in parentheses, but far more are known to science (Invasive Species Compendium). If selecting chemical management options, choose reduced risk insecticides that will protect the natural enemies that reduce hemlock looper populations.

Chemical Management: 

Abamectin (NL) 

Acephate (NL)

Acetamiprid (L)

Azadirachtin (NL)

Bacillus thuringiensis subsp. aizawai (L)

Bacillus thuringiensis subsp. kurstaki (NL)

Beauveria bassiana (NL)

Bifenthrin (NL)

Carbaryl (L)

Chlorantraniliprole (NL)

Chlorpyrifos (larvae) (N)

Chromobacterium subtsugae (NL)

Cyantraniliprole (NL)

Cyfluthrin (NL)

Deltamethrin (L)

Emamectin benzoate (L)

Flonicamid+cyclaniliprole (N)

Gamma-cyhalothrin (L)

Horticultural oil (L)

Lambda-cyhalothrin (L)

Methoxyfenozide (NL)

Neem oil (NL)

Pyrethrins (L)

Pyrethrin+sulfur (NL)

Spinetoram+sulfoxaflor (N)

Spinosad (NL)

Tebufenozide (NL)

Tau-fluvalinate (NL)

Zeta-cypermethrin (L)


Active ingredients that may be applied systemically include: abamectin (injection), acephate (injection), acetamiprid (injection), azadirachtin (injection, soil drench), cyantraniliprole (soil drench, soil injection), emamectin benzoate (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.

Read and follow all label instructions for safety and proper use. If this guide contradicts language on the label, follow the most up-to-date instructions on the product label. Always confirm that the site you wish to treat and the pest you wish to manage are on the label before using any pesticide. Read the full disclaimer. Active ingredients labeled "L" indicate some products containing the active ingredient are labeled for landscape uses on trees or shrubs. Active ingredients labeled "N" indicate some products containing the active ingredient are labeled for use in nurseries. Always confirm allowable uses on product labels. This active ingredient list is based on what was registered for use in Massachusetts at the time of publication. This information changes rapidly and may not be up to date. If you are viewing this information from another state, check with your local Extension Service and State Pesticide Program for local uses and regulations. Active ingredient lists were last updated: January 2024. To check current product registrations in Massachusetts, please visit: .