Identifying Insect Cocoons in Your Landscape and Garden

Many insects create a cocoon for protection during an early stage of development, called the pupal stage, in which they dramatically transform from an adolescent larva (such as a caterpillar) to their adult form (such as a butterfly). This is called metamorphosis. When encountering cocoons in your landscape and garden, it’s important to identify the cocoon type to be sure you’re not harming a potentially beneficial and beautiful insect that’s part of your landscape’s ecosystem. Insects typically start the pupal stage in fall and metamorphose over winter, emerging as an adult in spring. The structure shown here, technically called a chrysalis (more on that in a bit), houses a developing butterfly.

To identify a cocoon, first take note of a few key things: cocoon shape, material, color, and placement in the garden or landscape, as well as time of year. Cocoons may be hanging from trees but they may also be tucked into shrubs, brush or piles of leaves. You can also observe what insects are nearby, which serves as a clue to what’s inside. Wondering what to do with a cocoon you’ve spotted? As with most insect interaction in your garden, it’s best to do nothing if you don’t have good identification — and good reason — to do something. Just observe at first. This cozy cocoon belongs to a bagworm pupa.

Most moths create cocoons of silk. Moth caterpillars spin the silk to make their cocoons, producing the silk through a tubelike “spinneret” located near their mouth. Moth cocoons can be oval-shaped and hang from trees, but they can also be found in other locations. The cocoons typically start out white and mature to brown, but they may also be covered in other natural materials like dead leaves, as is often the case with Luna moth cocoons. To encourage Luna moth (and other beneficial insect) populations, leave some of the fall leaves in your yard over winter. Here, silk moths emerge from a silky cocoon.

While they’re very similar, butterflies don’t actually create cocoons like moths do. For their pupa stage, butterflies develop a chrysalis, which is a hard case surrounding the developing butterfly. Like a moth cocoon, you will often spot a butterfly chrysalis hanging from a tree, but it will more likely be green — easy to mistake for a fresh leaf, though it may also be camouflaged by dead leaves, as is the case with Swallowtail butterflies. Butterfly chrysalises become translucent through the pupal stage as the caterpillar metamorphoses into a butterfly, and you can sometimes see the butterfly inside. In this photo, the monarch’s wings are visible just before hatching from the chrysalis.

This monarch butterfly has newly emerged from its chrysalis on a milkweed plant.

Praying mantes are beneficial in the landscape and garden because they feed on other insects, including mosquitoes. You may spot their egg sacs, which look like cocoons (but technically aren’t), in fall and winter on shrubs and trees. In the early stage, the egg sacs have a foamy appearance, but this hardens through winter.

This praying mantis is in the process of building a nest to protect its eggs.

Many wasps, including Braconid wasps, are highly beneficial in the garden because they parasitize insect pests, such as tomato hornworms and armyworms. The wasps pierce the hosts and lay eggs inside them. When the wasp larvae hatch, they feed on the host caterpillar or worm from the inside out, eventually killing it. When the larvae approach the pupal stage, they create little individual cocoons outside the host’s body. In this photo, a tomato hornworm is covered in parasitic wasp cocoons.

Braconid wasps are highly beneficial in the garden, feeding on pest caterpillars.

Other kinds of wasps make unique cocoons using mud. Sceliphron wasps are also called “mud daubers” and Eumenine wasps are called "potter wasps." They create these nests using clay, typically on the undersides of structures such as under roof eaves or barns where the nest is safe from rain. While the mud structures are technically nests, the pupa stage occurs within cocoons inside the mud nests. Mud dauber and potter wasp nests may be considered a nuisance visually but the wasps themselves are largely harmless.

This industrious mud dauber wasp is gathering a ball of mud.

Cocoons on conifers such as cedar, juniper and arborvitae may be evidence of bagworms, which can harm these evergreens. Bagworms are the caterpillar stage of a type of moth, and they craft cocoons out of silk along with bits of the host plant. The caterpillars start spinning these cocoons soon after they hatch in spring, building their “bags” and carrying them with them throughout summer. In late summer, they attach their cocoons to a fixed spot to begin pupation. These bags can be removed and thrown out to avoid plant damage.

Bagworms will destroy conifers; here, a bagworm munches on a cedar tree.