Your question about bag worms is very relevant this time of year.  Although the critters hatched in spring, they only become large enough to notice now.  I copied pics and information from Maryland's extension service that I thought would be relevant.  You did not include which trees you found your bagworms.  This info will help if this is the right pest.  If not, let me know , send a pic, and I will try again.

Bagworms on Chinese juniper. Photo: Eric Rebek, Oklahoma State University, Bugwood.org

Updated: April 21, 2021ShareFacebookTwitterPinterestEmailPrintFriendly

Bagworm (Thyridopteryx ephemeraeformis (Haworth), is a serious insect pest of many ornamental shrubs and trees in the eastern half of the United States. Conifers, especially arborvitae, cedar, juniper, and pine are the most frequently damaged host plants.

Deciduous trees such as sycamore, maple, locust, boxelder, and linden are also attacked but they are not seriously damaged. This pest is sometimes confused with Eastern tent caterpillar.

Appearance and habits

• Bagworms are actually the larval or caterpillar stages of moths.
• After hatching,  they immediately spin a small 1/8 inch long cocoon-like bag to which are attached pieces of leaves from the plants they feed upon. If you look closely, you will see them moving around as they feed on the plant.
• Bagworms move about freely to feed, and they carry their bags with them. The bags gradually enlarge as they feed during the summer to house the growing caterpillar.
• They spread from tree to tree by ballooning (they spin a fine web and use wind currents to infest nearby trees).

Life cycle

•  the eggs hatch sometime in May.
• Bagworms complete their growth in August or early September. At this time, the 1-2 inch long bags are permanently attached to plant twigs by means of tough silken threads.

• In late summer, they pupate inside the bags and then transform into moths, but only the males have wings.

• The males emerge from their bags in late summer and fly to the bags containing females. The males mate with the wingless females which remain in their bags.
• Then each female lays 200 to 1,000 eggs in its bag and dies. The eggs remain in the bags until hatching occurs the following spring.

Damage

• When populations are high, bagworms are serious defoliators of plants. They cause permanent damage to evergreens.
• Shrubs and trees that become heavily infested, particularly conifers, may be killed.
• Injury is not conspicuous early in the season because the caterpillars and their bags are small. The bags are not easily seen at this time unless large numbers are present. Bagworms often are not detected by the untrained observer until August after severe damage has been done.

Management

Mechanical control

• On landscape shrubs and small trees, a simple method of control is to pick off the bags during the fall, winter, and spring.
• Do not throw them on the ground near the trees but destroy them and throw them in the trash.
• Remove the bags in any season but do it before the new generation hatches out in May or early June.
• When too many plants are involved, to make hand picking practical, sprays are in order.

Biological control

• Bacillus thuringiensis, often called Bt, is a type of bacteria that only kills certain insects and does not affect humans or animals.
• Bt must be applied by mid-July because it works well only on young bagworms.
• Bt is commercially available under the following common brand names: Dipel, Thuricide, and others. Many of these brands are sold in local hardware stores and garden centers.
• Use according to label directions. Multiple sprays may be necessary.

Chemical control

• If chemical control is absolutely necessary, a registered insecticide should provide control if applied thoroughly to all infested plant foliage after July 15.
• Check the label on the pesticide to be sure bagworm and the type of plant you wish to spray are listed.
• CAREFULLY FOLLOW ALL LABEL DIRECTIONS WHEN MIXING AND APPLYING THE SPRAY.

Without a picture of your pest, and since you just noticed the webs in August, I think I have another choice, fall webworms.  This article from New Hampshire Extension may be of help.

The fall webworm (Hyphantria cunea) and the Eastern tent caterpillar (Malacosoma americanum) feed on fruit, shade, and woodland trees. They are of little economic importance in orchards which are regularly sprayed to control codling moths and other pests. Because they form unsightly webs, however, they can be considered a significant pest of nurseries and landscapes.

The fall webworm is frequently confused with the Eastern tent caterpillar. The dirty loosely-woven web of the fall webworm encloses branches; the larvae can be found feeding within this web. The web of the Eastern tent caterpillar, on the other hand, is thickly constructed in the forks and crotches of trees; the larvae do not feed within their webs, but congregate there at night and during rainy weather. Fall webworms occur in summer and fall, whereas eastern tent caterpillars appear in spring.

Description

Fall Webworm: Full-grown larvae are about 1 1/2" long. They may be yellow with dark stripes and spots, or they may be a dull bluish black without yellow. Their bodies are very hairy, and heads are dark. Adult moths have a wingspan of 1 1/2". Their color is nearly pure white.

Eastern Tent Caterpillar: Full-grown larvae are about 2" long with sparse hairs. They are black with white and blue markings and have a white stripe down the middle of the back. Adult moths are reddish-brown with two whitish stripes running obliquely across each forewing.

Life Cycle

Fall Webworm: There is one generation of fall webworm per year, but it is not very synchronous. The insects overwinter as pupae in the soil. In June and July, the adult moths emerge from the soil. Females begin laying their masses of eggs in July. The eggs begin to hatch in mid-July. The larvae feed within the web for one month or more, crawl down the tree, construct a cocoon, and pupate.

Eastern Tent Caterpillar: There is one generation of the Eastern tent caterpillar per year. The insects overwinter as egg masses on twigs, and they hatch in April. After feeding for two days, larvae weave their tent. Successive layers are added to the tent as the larvae develop. Early in summer, the larvae spin cocoons, pupate, and emerge as adults. The females deposit masses of eggs in bands around twigs. The larvae develop inside the eggs, but do not hatch until the next spring.

Management

IPM Strategies:

• Monitoring - Looking for and destroying tent caterpillar egg masses can reduce the need for treatment. Early detection of webs of either pest is important to avoid excessive defoliation.
• Cultural Practices- Destroy nests by pruning or removing by hand (a stick may be inserted into large webs and twisting it loosens the webs).
• Biological Control - Several natural enemies keep the populations of both the fall webworm and the Eastern tent caterpillar in check, including birds, small mammals, insect predators, spiders, and parasitic wasps. A naturally occurring virus and a fungus can reach levels that kill many caterpillars of both species when humidity and temperatures are right. Biological insecticides based on Bacillus thuringiensis (Bt) can be used for either pest and should be applied when the tents are first noticed and the larvae are still small.
• Chemical Control - Apply pesticides to hard-to-reach infestations or when populations are heavy. Consult your county Agricultural Field Specialist for specific pesticide recommendations.

As the article suggests, this is not the time to see eastern tent caterpillars.  Hope this solves the mystery.