Other Common Names
Fall Webworm (larva)
Écaille fileuse - En français… Ilze V-G.
Synonyms and other taxonomic changes
Phalaena cunea Drury 1773
Hyphantria cunea
Explanation of Names
CUNEA: from the Latin "cuneus" (a wedge) or "cuneatus" (wedge-shaped); perhaps a reference to the shape of the dark markings on the forewing of some individuals
Numbers
common to abundant throughout range
Size
wingspan 25-42 mm
larva length to about 25 mm
Identification
Adult: wings either all white (in northern and some southern individuals) or sparsely to heavily marked with dark grayish-brown to black spots (in many southern individuals); spots rectangular or wedge-shaped, arranged loosely in rows in basal half of wing, and in either a V-shape or more-or-less random arrangement in distal half; ventral side of prothorax and femur of foreleg with orange hairs; hindwing either all white or with one or two black spots
Larva: two distinct races - northern larvae have black head, yellowish or greenish body with dark dorsal stripe and long whitish hairs arising from black and orange tubercles located along sides (in each cluster of hairs, at least one hair is about twice as long as the others); southern larvae have orange or reddish head, yellowish-tan body with orange to reddish tubercles and brownish hair. Wagner
(1) lists extremely long hairs, "greater in length than four or five body segments," as an identifying characteristic.
Note: This species is very often confused with Spilosoma congrua and S. virginica where ranges overlap. When a view of the abdomen is not possible, one of the key clues as to which species, lies with the appearance of the legs: in particular, the tibiae and tarsi of the forelegs. The key to using this characteristic to separate these three species is as follows:
S.congrua; tibiae and tarsi will be solid white laterally, bordered by solid black medially along the interior of the tibiae/tarsi with a clear demarcation and no banding on tarsi.
S.virginica; tibiae and tarsi will be strongly white with complete or partial black banding along the tarsi.
H. cunea; tibiae and tarsi vary – in immaculate specimens the tibiae/tarsi is often completely white/pale, while in heavily marked specimens, the tibiae/tarsi are completely black. In other lighter marked specimens, tarsi may appear banded and most similar to S.virginica, but will only appear so laterally with solid black/dark medially. When dealing with this variation, it’s typically described as H.cunea having dark tibiae/tarsi, the tarsi banded with white, verses S.virginica having mostly white tibiae/tarsi, the tarsi banded with black.
Where an egg mass is present, another clue is available. The egg masses of S.virginica are typically yellow, of S.congrua typically white, and those of H.cunea, a very pale green.
Range
All of United States and southern Canada plus northern Mexico
Accidentally introduced from North America to Yugoslavia in the 1940s, and has since spread throughout Europe; later introduced to northern China and North Korea
Habitat
Weblike tents in branch tips where clusters of caterpillars strip foliage (by contrast, eastern tent caterpillar nests are built in tree crotches)
Adults are nocturnal and attracted to light
Season
Adults fly from May to July in the north; March to August in the south (or all year in Florida)
Caterpillars are found June to September or October in the north; May to October in the south. Larva are most often noticed when they reach final instar and wander out of their home trees to find a place to pupate.
Food
About 120 species of hardwood trees have been recorded as larval hosts
In the north, common hosts include alder, apple, ash, birch, Box-Elder (Acer negundo), cherry, elm, mulberry, poplar, willow
in the south, common hosts include ash, hickory, maple, mulberry, oak, pecan, poplar, redbud, sweetgum, walnut, willow; preferences for different host plant species appear to be regional and seasonal
Life Cycle
one generation per year in the north; up to four generations in the south; up to 1,500 eggs are laid in a mass on undersurface of leaf of host plant; female covers the eggs with white hairs from her abdomen; larvae molt up to eleven times through successive instars before leaving the web to pupate; overwinters as a pupa in silken cocoon under bark flaps; adults emerge in spring
Larvae feed on foliage throughout their development, and secrete silk which they spin into small webs. As they grow, they enlarge the webs, which can sometimes enclose the entire tree. Even severe infestations have little impact on trees because the damage occurs near the end of the annual growing season. Except in the case of ornamental trees, control is seldom necessary because the damage is generally of aesthetic rather than economic importance.
Remarks
The parasitoid Psychophagus omnivorus (Pteromalidae) is a very effective natural enemy which attacks pupae. It has been reared and released for biological control of Fall Webworm.
A wide range of tachinid fly species parasitize it
Entomologica Fennica
Additional hymenopteran and tachinid parasitoids are listed by the
University of Florida.
Telenomus bifidus is a wasp in the Scelionidae family that parasitizes the eggs.
(2) See Also
adult
Pink-legged Tiger Moth is very similar but has pink or reddish hair on foreleg femora
adult
Agreeable Tiger Moth (
Spilosoma congrua) has sparser and smaller spots on forewing
adult
Virginian Tiger Moth (
Spilosoma virginica) has wings with no or a few small spots, abdomen with yellow and black bands, and foreleg femora with yellowish-orange hair
adult
Dubious Tiger Moth (
Spilosoma dubia) has wings heavily spotted with black
adult
Vestal Tiger Moth (
Spilosoma vestalis) has unspotted wings and foreleg femora with red hair
adult
Satin Moth (
Leucoma salicis; Lymantriidae) has unspotted satin white wings, grayish-black abdomen, and legs with alternating black and white marks
Print References
Caterpillars of Eastern Forests
(3)
Caterpillars of Eastern North America
(1)
