Elm Spanworm – Ennomos subsiggnaria

Elm Spanworm – Ennomos subsiggnaria Common Name: Elm Spanworm Latin Name:  Ennomos subsiggnaria Appearance:

• Adults are powdery white moths with 30-37mm wingspan. Each wing has a characteristic light tan patch in the centre of the underside. The mature female is somewhat bigger than the male, with slender antennae and a thicker abdomen.
• Larvae are up to 50mm long and vary in color depending on population density. Larvae in big outbreak populations have a dull slate black body with a rust-colored head capsule, but larvae in small outbreak populations might be consistently green, yellow, mottled brown, tan, or rose.
• Pupae are light brown and sometimes speckled with hooklets.
• Eggs are Barrel-shaped with an amber-colored ring on the exposed end, approximately 0.5mm. Eggs are pale green when first deposited in the summer and darken grey in winter. Eggs are placed in irregular compact masses (2-2.5cm broad) on the undersides of twigs.

Host plant: Elm, Ash, Hickory, and Walnut Territory: The elm spanworm is native to North America, with a range that includes the Eastern United States and Southeastern Canada. Damages caused by Elm Spanworm: The Elm spanworm is a serious defoliator of woodland and shade trees. It can entirely defoliate huge swaths of mixed hardwood forest during outbreaks. It is also a significant pest to urban trees. Damage rises with each successive year of defoliation; after the first year, damage may be limited unless trees are stressed, but after two years of severe defoliation, significant growth loss, branch dieback, and tree mortality are possible. Life history and Habits: Elm spanworm eggs overwinter on the underside of twigs, branches, or the trunk. The eggs hatch when the tree buds open in mid to late May. For the first few instars, the larvae emerge and begin eating gregariously on the underside of leaves, giving a shot-hole appearance. Mature larvae consume all leaf material between the main veins. Feeding takes roughly a month to finish. The larvae create coarse net-like cocoons of silken threads that “hooklets” attach to partially defoliated leaves, branch ends, or bark fissures (small barbs protruding from the pupa). Adults emerge 9-17 days later, from late June to July, and lay eggs from July to August. Each year, there is one generation.