Question
Hello Jim,
I recently relocated from Ca to Pa and have notices a big difference in bugs out here. It appears that when you move to Pa in the more rural areas you get free membership to the bug of the month club. Last week I noticed what looked like netting wrapped around the tips of tree branches. At first I thought something just blew into the tree, but there were too many. They all seemed to appear within days of each other covering many trees. I get creep ed out by it when I drive past them. What kind of spiders are they? Is the massive net an huge egg sack? Yikes!!! I live in the south-east part of PA, just outside Pottstown. Last month we had some type of beetle, followed by what I thought were "butterflies", which turned out to be grubs. I'm I little freaked out about going outside. Funny thing is, I taught preschool in my home back in Ca and we hatched butterflies, silk worms, lady bugs and praying mantis eggs. We would regularly look under rocks for bugs. But out here in PA, everything is bigger and seems to fly.Do you know of who I could go to or how I can find out about all these new creatures where I now live. Thanks for any info you can give me.
Cathy Taormino
Teddy Bear Play School
(408) 823-7279
11 Robins Nest Lane
East Coventry TWP, Pottstown
PA, 19465

Answer
The webs are from an insect called Fall Webworm.
The fall webworm, Hyphantria cunea (Drury), is most often discovered when the unsightly, light gray, silken webs on the trees in late summer and early fall are observed. Webworms enclose leaves and small branches in their nests, unlike the tent caterpillars which make a smaller nest in the crotch of branches.

This pest is native to North America and is common from Canada into Mexico. It is one of the few American insect pests that has been introduced into Europe and Asia. Fall webworm larvae have been known to feed on over 85 species of trees in the United States.

The large silk webs enclosing tips of branches are sure signs of fall webworms. The caterpillars remain inside the webbing, and if food runs out new foliage is encased. The caterpillars are covered with long white to yellowish tan hairs. Two races of fall webworms occur in North America, the blackheaded and redheaded races. The blackheaded race has caterpillars which are light greenish-yellow to pale yellow with two rows of distinct black tubercles. The redheaded race is more tan in color with orange to reddish tubercles. The caterpillars make distinct jerking movements in unison if the nest is disturbed. The adults are about one inch long and range from pure white to white with a few black spots.

This pest overwinters in the pupal stage. Pupae are usually in the ground but can be located in old nest remains, under loose bark and in leaf litter. The adults emerge from late May into July. The eggs are usually deposited in a single (blackheaded race) or double (redheaded race) layer of several hundred eggs on the undersurface of leaves. The mass is lightly covered with scales from the female's abdomen. The eggs hatch in about a week and the small mass of caterpillars web over single leaves and feed by skeletonizing. As the caterpillars grow, they web over additional leaves and finally are able to eat the entire leaf. The larvae mature in about six weeks, at which time they drop to the ground to pupate.

Though the webs are very unsightly, damage to most trees is considered to be insignificant. However, in southern states where several generations of attack can severely defoliate trees, control measures are needed. This pest tends to go through periodic population explosions. Outbreaks every four to seven years may last for two to three years and then natural control agents greatly reduce the activity.



Biological Control - Apply Bacillus thuringiensis (Bt) - The bacterial insecticide, Bt, is quite effective against fall webworms if it is applied when the larvae are small. Use formulations with UV protectants and thoroughly cover leaves next to nests. As these leaves are incorporated into the nest and eaten, the Bt will be ingested.

Chemical Control - Standard Insecticide Sprays - Most applicators attempt to "blow" the nest out of the tree with a strong jet of insecticide mix. While this generally works, more material is often used than is needed. Locate nests early and merely wet the nest and cover nearby foliage. As the larvae walk on the nest surface or incorporate new foliage, they will contact the insecticide. Second applications may be needed if additional generations occur.  

In most situations, the only thing that can be done is to maintain good tree nutrition through proper fertilization and water the tree during dry periods, if possible. If a chemical treatment is practical, Orthene Turf, Tree and Ornamental Spray7 is a registered for webworm control on ornamental trees only (Do Not Use On Pecans). Liquid Sevin, (21.3%) may be used on pecan trees. In both cases follow label directions on the product of choice for proper mixing instructions and other safety information.


Chemical Control - Use Systemic Insecticides - Extensive nests may occur in tall trees which are difficult to spray with ground equipment. These trees can often be treated with translocated systemics applied to the soil for root uptake or injected.