Common Cocoons and Egg Cases in the Garden

As you're trimming the hedges in the late winter, you encounter a strange egg sac. Is it a cocoon for a pretty butterfly, or the eggs of something bad that will destroy your plants? It can be difficult to determine at a glance whether a bug is good or bad for your garden simply by examining the egg case or cocoon, but a few examples can help.
Most garden insects are actually GOOD for your garden, or at least neutral. The majority of moths, worms, and other insects are beneficial and contribute to the overall health of your garden's ecosystem. Let's take a look at a few who contribute to the garden, and one who can harm it.
The bagworm caterpillar is a fascinating, albeit destructive, creature. The female spins a bag and lay eggs inside the bag. When the larvae hatch, they can quickly eat their way through and entire tree. We found this cocoon on our apricot tree and had to destroy the bagworm cocoon. Note, however, the intricate camouflage created around the bag; pine needles and sticks were used to hide it from predators.
I found this walnut-sized egg case on the forsythia hedge. Do you recognize it? If you don't, try to learn it by sight, because it is the egg case of the wonderful praying mantis. The praying mantis lays approximately 100 eggs in a case like this. The nymphs emerge in the spring like mini adults, ready and able to eat all the bad bugs in the garden. They eat flies, moths, grasshoppers and crickets. Praying mantids are so beneficial that many organic gardening catalogs sell the egg cases to gardeners to add them to their gardens! I'm lucky to have several this year. These guys stayed right where they are!
The last image shows an interesting cocoon I also found on the forsythia hedge this winter. There were several similar cocoons. I was able to identify it as the prometha moth. These gentle creatures do not harm the garden, so I left it alone.
When you need to identify an insect, egg case, or cocoon, you can try several things. First, take a photograph of it. Next, you can use a reverse image search such as Google Image search to upload your picture and see if it matches one online. This is how I was able to identify the prometha moth; it called up similar cocoons, with websites explaining the insect and showing images that matched my own. If you would like a more personal identification of your particular insect, contact your local Cooperative Extension office. Bring a picture of the insect and details about where you found it (or the egg case/cocoon) for a positive ID.

Jeanne Grunert
Want more details about this and other DIY projects? Check out my blog post!

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2 of 27 comments
  • Barbara Sullivan Barbara Sullivan on Feb 16, 2015
    We break bag open & let bird's enjoy them..

  • Renata Renata on Feb 17, 2015
    Thank u for ur info. I have these cocoons around my place that I have no idea nor do my friends what is. With your info on Google site I can find out.