A reader recently wrote to us asking how to control the inchworm infestation of their oak tree. Inchworms (commonly written as “inch worms”) are known to infest vegetation such as trees and shrubs, making them a pest for landscapers, farmers, and gardeners. First, we’ll discuss what inchworms are – answering the question “what is an inchworm?” – and then we’ll move onto the question of controlling an inchworm infestation.
First, an inchworm is not actually a worm – it is a caterpillar, the larva of a moth. Alternatively called measuring worms, cankerworms, spanworms, and loopers, inchworms generally measure between one centimeter and one inch (an inchworm is quite literally an inch worm). They come in many different colors – ranging from pale and reddish greens to brown and black hues – and they have stripes that run down their sides and back. Often, their heads are a pale green color and are covered with black spots. Inchworms are hairless and smooth, and several species have patterns on their bodies that help them mimic plants. With this information, you should be able to spot inchworms, which are abundantly present in North America.
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As we mentioned above, inchworms can cause considerable damage to trees and plants. However, before moving on, it is worth mentioning that a small, controlled number of inchworms are not necessarily harmful, so if you see an inchworm in your garden, you needn’t immediately panic. That said, inchworms are a nuisance in large numbers, and this is easy enough to see when you look at an infested plant, which will have small holes between its veins thanks to the inchworms relentless feeding. And that is exactly what you must keep in mind when evaluating an inchworm threat: they damage vegetation by consuming it, so it is no surprise that a few inchworms is nothing to be too concerned about, while a large number is something that needs to be addressed.
An inchworm infestation left unchecked can become a serious problem because female moths (i.e., the mothers of inchworms) lay eggs in the fall and spring. Populations of inch worms can skyrocket quickly. But the question remains: how do you control an inchworm infestation?
First, there are preventative measures one can take to protect against an infestation, and one of the main ways involves fighting nature with nature. Inchworms have a number of natural predators, so if you allow these creatures – insects like yellow jackets, wasps, and ground beetles, as well as animals like birds – to flourish in your garden, yard, or crop field, they can keep the inchworm population in check. There are also natural diseases, like wilt disease, that afflict inch worms, and these help control inchworms too.
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If these natural lines of defense fail you and you are stuck with an infestation, you may have to turn to other remedies, which are beyond the scope of this article.