Spongy moth: Fact sheet

Identification

Adult

Male moths are much smaller than females and have a wing span of 35 to 40 mm. Females have a wingspan of 55 to 70 mm. Males are brown, whereas females are mainly white. Both sexes have a dark, crescent-shaped mark on the forewing.^{Footnote 1 Footnote 2} Both sexes also have pectinate antennae, however the males have longer branches that give their antennae a more feathery appearance.

Larva

The first (3 mm) and third (7 mm) instars are black with long hairs; the second instar (5 mm) is brown with short hairs. Instars 4, 5 and 6 are similar to each other and may be light to dark gray with flecks of yellow. They have long hairs that may be dark or golden and have 2 rows of tubercles along the back. Normally 5 pairs of blue tubercles are followed by 6 pairs of red. However variations are known to occur, including all 11 pairs of tubercles being blue.

Egg

Ovoid egg masses are covered with tan-coloured hairs from the female's abdomen. They eventually become sun-bleached with age. Egg masses are approximately 30 to 60 mm long and 20 to 30 mm wide and may contain 100 to 1000 eggs.^{Footnote 3} Spent egg masses have pin sized holes caused by emerging larvae.^{Footnote 2}

• Plant pest card – Spongy moth Lymantria dispar dispar

Host trees

Quercus (main host), Acer, Alnus, Betula, Crataegus, Fagus, Malus, Populus, Prunus, Salix, Tilia and many other tree and shrub species.^{Footnote 4 Footnote 2}

Location of infestation within the tree

Larvae feed on foliage within the crown.^{Footnote 1}

Host condition

Healthy trees.^{Footnote 3}

Distribution

Europe, northern Africa, eastern Canada and northeastern USA.

Signs and symptoms

Typically near their pupation sites, female moths lay egg masses on tree bark, branches and other protected places, including rock piles, lawn furniture, bird houses, piles of wood, beneath logs, underneath recreational vehicles or equipment, etc.^{Footnote 3} Early instar larvae excavate small holes in leaves and feed gregariously.^{Footnote 1} As the larvae grow they make larger holes and they also consume the leaf margin. Final instar larvae will consume the entire leaf. At high populations, larvae can strip all leaves from a tree. At low populations, feeding may be barely noticeable, and larvae may be difficult to find since they prefer to rest in dark locations under bark flaps, stones, litter on the ground, etc.^{Footnote 3} Larvae seek sheltered places to pupate.^{Footnote 5} Pupae may be found attached by silken thread to branches, tree trunks, rocks, forest debris, buildings or fences.^{Footnote 5} During outbreaks large amounts of frass may fall from defoliated trees.^{Footnote 3} When food is scarce, larvae will also feed on unripe tissues of annual shoots, flowers and buds.^{Footnote 1} 1 year of defoliation may not kill a healthy tree. Severe defoliation can reduce tree growth and predispose trees to attack from other insects and diseases. 4 successive years of defoliation can cause mortality, especially in weakened or stressed trees.^{Footnote 6}

• Image 1: Larger and mainly white female (top). Smaller and mainly brown male (bottom). Note dark crescent-shaped mark on forewings
• Image 2: Female spongy moth ovipositing an ovoid egg mass. Egg masses are covered with tan coloured hairs from the female's abdomen
• Image 3: Spongy moth larva. Note 5 pairs of blue tubercles are followed by 6 pairs of red
• Image 4: Defoliation by early instar spongy moth larvae. Note small holes in the leaves
• Image 5: Extensive stand defoliation caused by spongy moth
• Image 6: Extensive stand defoliation caused by spongy moth