Ames Free Library

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A Glimpse of Nature -- Egg Cartons

Last week’s “What Is It!” game featured two structures that facilitate reproduction for their creators. The animals who produced these “egg cartons” were, however, vastly different.

A Baltimore oriole wove the sack-like nest in the first image.


This beautiful species can be seen and heard at the Ames Free Library during its breeding season. 

June 9, 2022, Ames Free Library

Orioles prefer open deciduous woodlands and forest edges such as the library’s park-like grounds. During the warmer months, our property’s varied plantings generate the insects, fruit, and nectar that orioles need. Here’s one of “our” birds eating a juicy caterpillar.

May 17, 2022, Ames Free Library

 In autumn when these foods become unavailable, the birds head to Central America.

Fall and winter are the best times to find their nests and to become accustomed to the sites where Baltimore orioles build them. These birds nest high in deciduous trees. Prior to the introduction of Dutch elm disease, American elms were their preferred nesting tree. The library’s orioles have been choosing maples during the years that I’ve observed them. At the chosen site, the female anchors her nest to slender branches and creates the structure of the pouch using long fibers. As the nest takes form, she fills the gaps and lines the interior with soft cushioning. “Construction materials can include grass, strips of grapevine bark, wool, and horsehair, as well as artificial fibers such as cellophane, twine, or fishing line” according to Cornell’s All About Birds.  

Oriole Surrounded by Fluffy Willow Seeds, May 20, 2021, Pembroke

 The fibers are not woven in the human sense; rather, the bird pokes her beak in and out of the mass of fibers until the strands become tangled and knotted. These “thrust-and-draw movements” are described in “How Orioles Build Those Incredible Hanging Nests.” The article also includes a nice image of a female in the process of constructing a nest.

The mother-to-be works day after day to weave a strong, durable nest that can support her and her young throughout the incubation and nestling periods. This can take close to a month, but the nests are so well built that they usually last much longer. The beautifully crafted nest below remained intact until spring of the following year.

 Oriole Nest in Birch, April 23, 2020, Halifax

One might wonder why the oriole goes to so much trouble to create a hanging sock-nest. The advantage seems to be protection from predators who could climb heavier limbs or attack a shallow nest from above. The Baltimore oriole has certainly perfected the technique.

If you want to observe orioles next spring, use your ears!  This species’ sweet whistled song and nonmusical chatter are conspicuous if you know what to expect.  Practice by listening to audio on Audubon’s Field Guide to North American Birds or a similar site. Then look high into the lime green foliage. Maybe you’ll find a nest in progress.


May 17, 2022, Ames Free Library


Our second “What Is It!” is an ootheca, the egg mass of a praying mantis. These tan balls, which look like styrofoam, contain the insect’s eggs and a protective coating. According to Wikipedia, “Oothecae are made up of structural proteins and tanning agents that cause the protein to harden around the eggs . . . .”  This lightweight foam shields the eggs from predators and weather until they hatch the following spring.

Ootheca on Dogwood Shrub, November 28, 2022, Ames Free Library


At this time of year, egg masses may be found attached to shrubs and to weed stems in overgrown fields. As with many observation skills, it will take some practice to train your eyes to notice them. The egg mass shown above jumped out from a sea of red-twig dogwood because its shape and color differed from the surrounding vegetation.


The animal who laid these eggs was a Chinese mantis, the largest and most common mantis in our area.  There are no mantises native to Massachusetts, though iNaturalist includes a few reports of Carolina mantises that were observed at plant nurseries. The insects you see in our area are Chinese or European mantises, species that were first introduced to the U.S. over 100 years ago.  Distinguishing between adults of these two species requires attention to fine details such as striping on the head or spots under the forelegs. Surprisingly, it is easier to identify them by their egg cases. Oothecae of European mantises are tear-drop shaped and uniform in color, whereas the egg masses of Chinese mantises are round or cube shaped. See this article by the Brandywine Conservancy for clear photos and descriptions of both.

Mantis on Alberta Spruce, November 2, 2022, Ames Free Library

Until recently, I was pleased whenever I found a mantis in my garden, and I found them often. I didn’t assume that they were “beneficial” to humans in their prey selection, but I imagined they were part of the balance that kept living systems going. Besides, I tend to stick up for predators who often get a bad rap. When I realized that “praying mantises” are invasives with voracious appetites, my outlook began to change.


 Though marketed for pest control, mantises consume a wide range of insect prey. A recent study by a team of researchers at Wheaton College identified more than 270 prey species in the stomach contents of the mantises they examined through DNA analysis. The meals of Chinese mantises included true bugs, butterflies, moths, grasshoppers, spiders, bees, wasps, and more. Their report concludes, “The abundance of these invasive generalist arthropod predators in Massachusetts is concerning, especially given their broad diets which include many important native pollinators and predators.” Similarly, the author of the Brandywine blog recommended collecting and destroying the oothecae of invasive mantises to lessen their impact on the native Carolina mantis.


If the early winter landscape looks “dead” it’s because we don’t know how to read the signs. There is drama all around us, as species struggle with each other and the challenges of their environment. What new things will you notice this week?


*Congratulations to the readers who correctly identified the Baltimore oriole’s nest. And, to the rest of you:  Don’t be so shy! Learning comes through engagement and the willingness to fail.


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