Web Worms, Bag Worms and Eastern Tent Caterpillars: What’s the Difference?

published Aug 27, 2008
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Outside of using them for composting, worms just haven’t been on our radar. That is, until they invaded our Walnut tree (worm jerks!). So we sat down with our old friend Google and tried to find out exactly what was taking over our tree and how to make it stop. Were they web worms? Bag worms? Or the Eastern Tent Caterpillar? Find out the differences on each and how you can keep your trees in check after the jump.

We came across a fantastic, to the point article outlining the differences between the three types of tree worms.
Check out some of the main points below:

(Image credit: Steve Heap/Shutterstock)

Bag Worms

Often times people mislabel the bag worm. They are the sneakiest of the 3, as they camouflage their web with bits of the tree they are living on (as seen above). They are small and create little diamond shaped bags on arborvitae (fancy word for things in the cypress family), Leyland cypress, and juniper. To rid your trees of them, pick or clip them off of the limbs and drop the bags into a bucket of hot soapy water. If you would like to treat your trees before they become a problem, you can try insecticides. B.t. (Dipel), carbaryl (Sevin), and malathion are all labeled to control them. Just make sure to do it in June or early July so the insecticides will penetrate the web.

(Image credit: Anest/Shutterstock)

Fall Web Worms

The Fall Web Worm makes it’s appearance at the end of summer and into the fall (hence the name). They create large webs at the end of tree branches, bushes and shrubs. They feed on over 600 different types of trees although their tree of choice is one that is fruit producing. Web Worms may be white/yellow in color, or black. They are smaller in size and markings on them are typically hard to see without the help of a macro lens camera. They are easily taken care of with a long stick or pole. Simply pull down the web, which will leave the worms exposed to birds and insects. Carbaryl (Sevin) can be used to spray webs within reach. Make sure to spray the foliage closest to the web mass, as spraying the web itself doesn’t give good contact with the caterpillars. If the webs are not within reach, don’t worry; although they are unsightly they usually do not harm the tree’s overall health.

(Image credit: Jocelyn Bartone/Shutterstock)

Eastern Tent Caterpillar
The Eastern Tent Caterpillar is often times confused with the Fall Web Worm, although there are a few major differences. You can identify them by the location their web is spun and coloring. The Caterpillars form webs in the crotches of a tree in late spring-summer, while the fall web worms form their webs at the end of branches later on in the season. The Caterpillars are traditionally black with a gold or white stripe down their back. They are larger in size (like you would think of caterpillars normally being) and are most often found on wild cherry, crabapple, and apple trees but other kind of trees are occasionally infested. They create an “egg mass” that is typically black with white spots in which the caterpillars hatch from. If seen before hatching in the spring, they can be removed from the tree before suffering from an infestation. If you don’t happen to spot them until they go all Bob The Builder on you and begin the web building you have a few options. One is to pull the web down with a long stick or pole, shaking the caterpillars loose, and stepping on them (ew). The other is to clip that section of the tree down and burn it in a safe, designated area. Please, PLEASE do not try to light anything on fire while it is still on the tree. Aside from not being safe, it’s not healthy for your tree. Carbaryl (Sevin) is labeled for controlling Eastern tent caterpillar, but it must be used before the infestation occurs.

For those still holding onto the edge of their seats to discover what invaded out Walnut tree…. it’s web worms. Although, the webby mass that is in our tree isn’t as photogenic as the opening graphic which was found by Amber over at myaimistrue. She found these Eastern Tent Caterpillars while spending time outdoors back in April.

Heebie-Jeebies aside, these worms/caterpillars actually make pretty cool photography subjects if you can get past the wriggling and squirming of it all. Check out these cool flickr images we found:

This one happens to be our favorite. It’s like Shark Week… Insect style. You can check out ProfJosh’s flickr to see the play by play of this wasp taunting, and then eating a web worm. Gross, and totally awesome.