These little green worms are hanging from my trees on invisible silk threads and crawling all over my patio furniture. They walk by looping their bodies in a weird way. What is this thing?

Springtime brings a burst of life to our gardens and trees, but it can also bring some unwanted visitors. If you’ve noticed tiny green worms dangling from your trees on seemingly invisible silk threads and crawling across your patio furniture, you’re witnessing a natural phenomenon caused by the spring cankerworm. These small creatures might look harmless at first glance, but they can be a nuisance and a threat to your garden's health.

Understanding what these little green worms are and why they appear can help you manage their presence effectively. This article delves into the world of spring cankerworms, exploring their lifecycle, behavior, and the potential impact they can have on your outdoor space. With the right knowledge, you can mitigate their effects and enjoy your garden to the fullest.

Spring cankerworms, scientifically known as Paleacrita vernata, are a type of inchworm that belong to the family Geometridae. These caterpillars are typically light green to brown and measure about 1 to 1.5 inches in length when fully grown. They are called inchworms because of their characteristic looping gait, which gives the appearance of measuring the earth as they move. Spring cankerworms are a common sight in North America, especially in areas with deciduous trees.

These worms are the larvae of a moth species that is active during the early parts of the year. The adult moths are rather inconspicuous, with males having light gray wings and females being wingless. After mating, females lay eggs on the bark of trees, which hatch into the caterpillars you see in the spring.

The silk threads that spring cankerworms spin are not actually invisible, but they are very fine, making them difficult to see unless the light catches them just right. These threads are a survival mechanism, allowing the caterpillars to drop from tree branches to avoid predators or travel to new feeding areas. By suspending themselves in mid-air, they can also disperse more easily across a wide area, aiding in their search for food.

This behavior is particularly noticeable during windy days when the caterpillars use the breeze to carry them further away from their original hatching site. This aerial dispersal can result in them landing on patios, furniture, and other surfaces, much to the chagrin of homeowners.

Spring cankerworms, like all inchworms, move in a distinctive looping motion because they lack the full complement of prolegs that most caterpillars have. They possess only two or three pairs of prolegs at the rear end of their body, which forces them to contract and extend their bodies in a characteristic loop or arch as they move.

This type of movement is not only unique but also efficient for inchworms as it allows them to traverse a variety of surfaces, from leaves to branches, with relative ease. The looping gait also helps them maintain a low profile, making them less conspicuous to predators.

Spring cankerworms have a specific life cycle that is closely tied to the seasonal changes in their environment. The adult moths emerge in late winter to early spring, with females depositing eggs on tree bark. These eggs hatch into larvae, or caterpillars, in early spring, coinciding with the budding of leaves on deciduous trees.

The timing ensures that the young caterpillars have plenty of fresh foliage to feed on. After several weeks of feeding and growing, the caterpillars drop to the ground to pupate in the soil, emerging as adult moths later in the year to begin the cycle anew. This predictable cycle makes it easier for those with affected trees to anticipate and manage their presence.

Spring cankerworms are not harmful to humans or pets. They do not bite, sting, or carry diseases that can affect people or animals. However, they can be a nuisance when they appear in large numbers, as they can cover outdoor furniture and other surfaces, making outdoor spaces less enjoyable.

While they are not directly dangerous, it's still important to manage their populations because of the potential damage they can cause to trees and shrubs, which indirectly affects the health of your garden ecosystem.

The primary concern with spring cankerworms is their voracious appetite for leaves. In large numbers, they can defoliate trees, stripping them of their foliage and weakening them over time. While healthy trees can generally withstand a single season of defoliation, repeated attacks over several years can lead to reduced growth, increased susceptibility to diseases, and even death.

In addition to damaging trees, the presence of large numbers of caterpillars can lead to an unsightly mess on patios and other surfaces covered in silk threads and droppings, further impacting the enjoyment of your outdoor space.

Spring cankerworms are often confused with other green caterpillars, but there are a few distinguishing features. They are usually light green, with a slender body that can have a faint yellow or white stripe running down the sides. Their size, typically 1 to 1.5 inches when mature, also helps differentiate them from other caterpillars.

Their distinctive looping movement, which gives them the name 'inchworm,' is one of the most reliable ways to identify them. Observing them closely can reveal these characteristics, helping you determine if you are dealing with spring cankerworms or another species.

Spring cankerworms have several natural predators that help keep their populations in balance. Birds, such as chickadees and warblers, are known to feed on them, as do some species of wasps and beetles. These predators play a crucial role in controlling caterpillar numbers, especially during peak seasons.

In addition to predators, environmental factors like weather conditions can impact cankerworm populations. A late frost, for example, can kill off early hatchlings and reduce their numbers significantly. The natural ecosystem, when in balance, typically prevents cankerworm infestations from reaching problematic levels.

To keep spring cankerworms off your deck and patio furniture, regular cleaning is essential. Use a hose or pressure washer to remove any caterpillars and their silk threads from surfaces. Installing barriers or covers over furniture during peak seasons can also help prevent them from settling.

Consider setting up bird feeders to attract natural predators to your yard, which can help reduce caterpillar numbers naturally. Additionally, keeping trees well-pruned and healthy can decrease the likelihood of severe infestations by minimizing the available habitat for egg-laying.

One effective long-term control strategy for spring cankerworms is the use of tree bands. These sticky bands are wrapped around the trunks of trees to trap the wingless female moths as they climb up to lay eggs. Timing is crucial; bands should be installed in late fall or early spring, depending on your region.

Regular monitoring and early intervention can prevent severe infestations. Maintaining tree health through proper watering, fertilization, and pruning can also make trees less attractive to pests and more resilient in the face of defoliation.

In cases where spring cankerworm infestations are severe and causing significant damage to trees, it may be necessary to call in professional pest control services. Signs that it's time to seek expert help include extensive defoliation, repeated infestations over several years, or when natural control methods fail to reduce caterpillar numbers.

Pest control professionals can assess the situation and recommend targeted treatments, such as biological insecticides, that are safe and effective. They can also help implement long-term management strategies to protect your trees and garden from future infestations.