Updated: Aug 19, 2019
Giuseppe Baldi, GM Baldi Gardens, Inc
Our certified experts are here to answer the What, Where, Why and How of those pesky Bagworms you keep hearing about. Read more to find out how to spot them and what to do to get rid of them before they ruin your landscape!
Those are bagworms! These caterpillars don’t typically present a problem every year and you may notice small numbers of them in any given year, but some years they emerge in droves and can completely cover and defoliate trees. It looks like this is going to be one of those years!
Bagworms typically make their “bags” in conifers (junipers, cedars, cypress, arborvitae, pines, spruces, etc.) and some broadleaf shrubs. The females construct these bags to protect themselves, their eggs, pupae and larvae. There are many different species of bagworms each species has slightly different life cycles and growth habits. Most bagworms pupate in late summer and after about 3 weeks the adult moths will emerge from their bags. This typically coincides with mating season, after which the femaless will deposit their eggs and die.
The bags these caterpillars construct are woven from silk and are reinforced with layers of leaves, twigs and bits of bark. There is typically a small opening at the bottom of the bag where the worm can expel refuse and waste. There is also a larger opening near the top of the bag where the worm can exit to feed or make repairs to their bags as needed. This upper opening is closed by the worm before each molting period and before winter hibernation or pupation.
Adult male bagworms will exit their bags after pupation, in search of a mate, through the small lower opening and will generally leave their pupal skin protruding from the bottom of the bag. Adult males emerge as small moths which are black in color and have clear wings and feathery antennae. Adult females resemble maggots and do not have functioning eyes, legs or antennae. Their bodies are soft and yellowish-white in color. Once they have successfully mated they will lay their eggs, which could number up to 1,000, in the empty pupal case inside her bag. They then fall to the ground and die.
Bagworms have many natural enemies, including birds, insect predators and insect parasites. Often, the infestations are much too large to be controlled by natural methods. Removing the bags by hand is the preferred and most effective form of control. These bags must be disposed of as the eggs inside could still hatch if left on the ground. In cases where hand removal may not be practical or safe insecticide may be used, although timing of treatments can be tricky. Insecticides must be applied soon after eggs hatch so as to kill the pupae before they have a chance to form bags of their own. Once a bag is constructed it may be very difficult to treat as insecticides may not readily penetrate the bags.
So, how do you deal with bagworms in your trees? If you suspect you may have bagworms in your landscape it’s time to call in the professionals or remove them by hand yourself. If insecticide is to be used, be sure your service provider has been trained and is appropriately licensed and insured to work with insecticides.