The objects pictured are actually praying mantis egg cases (called ootheca, or oothecae as a plural), not cocoons. We have one native praying mantis species in Maryland, the Carolina Mantid, but the rest found here are all non-native and invasive. The shape of this egg case indicates it's not the native species and probably belongs to the Chinese Mantis. You can compare them with some examples in our Get to Know Your Local Mantis short blog article.

Some gardeners value any praying mantis in the yard (they are all generalist predators, meaning they can eat both garden pests as well as pollinators), but other gardeners choose to only allow the native species to remain, squishing egg cases of any others. It's up to you what you prefer to do; the non-native species are so widespread and abundant that removing a few from the local ecosystem probably won't have much impact, though it's good to support our native species if it's encountered.

We do see one pest insect in the photos -- a lone Indian Wax Scale on a stem behind one of the egg cases (circled on the attached photo). It's one of several non-native scale insect species commonly found on garden plants, though it rarely causes any serious plant damage. Since this particular scale is so visible with its white covering, a bit like a blob of gum stuck on the bark, it is fairly easy to find and pluck off by hand, avoiding the use of pesticides as the other management alternative (only if populations are high). Since this is the only scale we see, you can flick it off the twig or just ignore it.

One of the plants pictured appears to be a Japanese Barberry, based on the thorns and appearance of its bark. If so, they are invasive and we recommend their removal and replacement. Some cultivars are supposedly mostly sterile (not producing seed that can germinate in woodlands and other natural areas), but it would be safer not to trust that they won't also pollinate other naturalized barberry, allowing those plants to keep producing invasive seedlings themselves. You can learn more about barberry in the linked page above.

The other pictured shrub appears to be Burning Bush, and if so, it too is unfortunately invasive and similarly is best removed and replaced.

The third plant looks a bit like blueberry, or at the very least, doesn't seem to be one of our rampantly invasive species at least.

If it helps you decide what mantis egg cases to monitor, there is one way to tell if they are old (hatched in a prior spring) or fresh. The seam running vertically down the front center of the egg case (the side facing away from the stem it's attached to) will be intact for unhatched eggs and interrupted by slits or holes in cases that are old and empty. There are also natural predators of these insects, like very tiny wasps, that can kill eggs and cause them not to hatch; these will leave round holes in many locations around the surface of the egg case. At least one of the egg cases pictured appears to be old and therefore empty, but we can't quite see the seam on the other two since they are pictured from the side. When mantids hatch, they usually do so around late spring, but it can depend on temperature trends. They will only be about 1cm long at that point, looking like pale brown miniature versions of the adult. They disperse pretty quickly because otherwise they can cannibalize each other.

Miri

Thank you so much for such a thorough response! I now know a lot more about the praying mantis!

You're welcome!