Tree Pests: Bagworms, Tentworms, and Webworms

Several worm species invade trees, including bagworms, tentworms, and webworms. You’ll see these worms hanging in miniature bags on evergreens and building webbed communities in the crooked branches and at the leafy edges of deciduous trees. Some of these worms are harmless while others can decimate a beautiful green landscape.

Bagworms are among the most destructive. They appear as tiny ornaments on evergreens – and sometimes on deciduous trees – encased in a blend of silk and pieces of bark and other leafy debris. As larvae, they can emerge from the bags to feed and then retreat. Adult females develop into grubs and remain in bags until they mate and lay eggs. When near death, the females drop to the ground. Males, on the other hand, emerge and fly away in search of females, but are rarely seen.

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Controlling small bagworm infestations is a matter of handpicking the prickly casings from the tree. Larger populations require insecticide treatment. Growth stages occur at varying times of the year, depending on region. It is best to use chemicals when the larvae are young and, therefore, more vulnerable. Left untreated, bagworms can eventually defoliate a healthy tree, causing it to die.

Tentworms, or tentworm caterpillars, are also pests that can do considerable damage to deciduous trees. When populations are on the increase, they will also migrate to other types of vegetation. The typical tentworm colony will first hatch on the leaves and then form a tent-like web in the crooks of tree branches. From this safety net, they move to the outside and feed. The forest tent caterpillar often creates a silk shield on tree trunks. Eastern and Western tent caterpillars are most recognized for their unsightly – and large – webbings.

In healthy trees, these worms will destroy portions of the foliage, but may not cause long-term harm. Weaker varieties, however, can suffer by exhibiting less tolerance to disease and slowed growth. The caterpillars also migrate and are often nuisances as they throng inside homes and travel up walls, indoors and out.

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Webworm and tentworm identification is often confusing. Webworms also construct tent-like homes, but they form at the outer edges of a branch. Inside these massive webs, the worms feed on the leaves. While visually unappealing as writhing masses inside the silky web, these worms are less damaging than their counterparts. Most trees will recover by the following season.

Controls include insecticides and pruning. In addition, natural predators such as birds and wasps will attack if the web is split open with a stick or rake. Quite often, webworms are left alone, unless a food crop is at risk. They do not necessarily return every year

Approved chemical treatments for bagworms, tentworms, and webworms will vary from state to state. Check with your local pesticide control expert to review the best process for treatment. Hand removal and pruning will eliminate or suppress smaller communities.

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