Fall Webworm (Hyphantria cunea)

American Tent Caterpillar Moth (Malacosoma Americanum)

The Fall Webworm (Hyphantria cunea) also called the North American Fall Webworm, is an insect in the family Tiger and Lichen Moths (Arctiidae) and order Butterflies and Moths (Lepidoptera).9 Some taxonomists place this species in the family Erebidae with Arctiidae as a subfamily.1 The order name is from the Latin for "charming" (Lepido) and the Greek for "wings" (ptera).2 The family name is from the Greek for "bear" referring to the northern constellation the big bear and the Latin for "northern." The alternate family name is from the name of the Roman god of darkness, Erebus.7 The genus name is from the Greek for "weaver."2 The species name is from the Latin for "wedge-shaped."6 This species of caterpillar weaves wedge-shaped nests at the ends of tree branches in the late summer or fall.4 See the photograph above taken of a Fall Webworm infestation in a tree on the northeastern shore of French Hill Pond. This nest can persist well into winter. The Fall Webworm can be easily confused with the Eastern Tent Caterpillar but the Eastern Tent Caterpillar builds nests in the spring and constructs its nests in the crotch of tree branches not at the ends of branches.4,8 The Fall Webworm will build nests in any hardwood tree whereas the Eastern Tent Caterpillar prefers trees of the Rose (Rosaceae) family.8,9

American Tent Caterpillar Moth (Malacosoma Americanum) Detail

The caterpillar can be a variety of colors but the Fall Webworm caterpillar in the French Hill Pond area will normally be dark and orange with long white hairs on its body as seen in the photograph above. Apparent colors of this caterpillar will vary depending upon the lighting conditions. The adult moth is pure white in the northern part of its range.5,9

The web nests are built by the caterpillars from silk strands that they secrete. These messy nests will contain dead leaves and black fecal matter. The caterpillars will work inside and outside the nests. These insects can defoliate a tree or shrub but seldom do so in the French Hill Pond area. Even if these insects essentially defoliate a tree, they will do so late in the year and the plant will usually recover because it will have lost its leaves anyway. These insects attack only deciduous trees.5,9

The life cycle of a Fall Webworm begins when a female Fall Webworm moth deposits her eggs on the underside of a leaf on a deciduous, hardwood tree or shrub in middle to late summer. She will deposit hundreds of eggs on one leaf. In about a week, the eggs hatch and the larvae, that is caterpillars, begin to eat the surface of the leaf. As they grow, the larvae begin to eat whole leaves while constructing the tent in which they continue to feed. They will leave the tent to incorporate other leaves into the nest working towards the branch tips. The Fall Webworm caterpillar can grow to 1.4 inches (3.5 centimeters) long. This larva stage is from four to six weeks long after which the larvae pupate. The pupa settles in the bark, leaf litter or soil at the base of the tree where it spins a thin, brown cocoon about ½ inch (1.27 centimeters) long in which it overwinters. The adult emerges from the cocoon the next year as a white, hairy moth with a wingspan of up to 1.6 inches (4.2 centimeters). Fall Webworm moths in southern parts of North America have brown or black spots on their white wings. The moths around French Hill Pond tend to be pure white.1,5,9

The following photograph shows the top side of a Fall Webworm Moth found east of French Hill Pond. Note the few brown spots. Moths of this species found further south will have more brown or even black spots. This moth is in a relaxed state. In flight, the wings would stretch out to about twice the wingspan show in the photograph.

Fall Webworm Size

The next photograph shows the underside of this moth. Note the fewer markings on the wings. Also note the orange to yellow coloring on the front legs. These characteristics help differentiate this species from similar white moths.9

Fall Webworm Moth Underside

The microphotograph below shows the compound eyes and the maxillary palp (mouthparts) of the Fall Webworm Moth from the underside. Note the large number of ommatidia (light sensitive units) seen most clearly of the eye to the left.3

Fall Webworm Moth Eyes

The Fall Webworm is native to North America but has spread to Europe and the far east where it is considered a major pest. It is one of the most studied moths because it can severely damage ornamental trees.5,9

The members of the Arctiidae family communicate with one another by ultrasound for the purpose of mating or warning of threats. Fortunately, these noises are beyond the range of human hearing.7

One can reduce the damage from these insects by pruning the affected branches and destroying the nests or isolating them to prevent the pupa stage. Do not attempt to burn the nests on the trees. Pesticides may also be used to kill these insects but the chemicals required can be dangerous if applied improperly. Infestations are difficult to prevent and a nuisance to destroy.

References:

1. Bartlett, Tony, BugGuide - Species Hyphantria cunea - Fall Webworm Moth, Iowa State University Entomology, retrieved from http://bugguide.net/node/view/453?printable=1, 8/30/2014.

2. Hudson River Park Companion, Hyphantria cunea - Fall Webworm Moth, retrieved from http://virtualnaturecenter.weebly.com/fall-webworm-moth-hyphantria-cunea.html, 8/30/2014.

3. Milne, Lorus and Margery, The Audubon Society Field Guide to North American Insects and Spiders, Alfred A. Knopf, New York, 1988, p. 17 & 942.

4. Penn State Extension, Fall Webworm, retrieved from http://ento.psu.edu/extension/factsheets/fall-webworm, 8/30/2014.

5. Sourakov, Andrei and Thomson Paris, Fall Webworm, Hyphantria cunea (Dury) (Insecta: Lepidoptera: Arctiidae:Arctiinae), IFAS Extension University of Florida, 2014.

6. Traupman, John C.,Latin & English Dictionary, Bantam Books, 3rd edition, 2007.

7. Wikipedia.org, Arctiidae, retrieved from http://en.wikipedia.org/w/index.php?title=Arctiidae&oldid=614196061, 8/30/2014.

8. Wikipedia.org, Eastern tent caterpillar, retrieved from http://en.wikipedia.org/w/index.php?title=Eastern_tent_caterpillar&oldid=582905371, 8/26/2014

9. Wikipedia.org, Fall Webworm, retrieved from http://en.wikipedia.org/w/index.php?title=Fall_webworm&oldid=614069803, 8/30/2014.

 

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