Carnegie Museum of Natural History

One of the Four Carnegie Museums of Pittsburgh

Blogs from Powdermill Nature Reserve

Powdermill Nature Reserve is Carnegie Museum of Natural History’s environmental research center. Located 55 miles southeast of Pittsburgh in Rector, Pennsylvania, Powdermill is a field station and laboratory where researchers do long-term studies of natural populations in western Pennsylvania. In addition to being positioned for Appalachian-specific studies in ornithology, ecology, invertebrate zoology, and botany, Powdermill is a great place to spend a fun-filled day outdoors with the family.

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Tornadoes, Snails, and Sample Sizes

woman collecting snail species specimens
Abbey collecting snails after braving unkind vegetation. Photo by Tim Pearce.

In 2012, a tornado felled trees in four places at Carnegie Museum’s field station, Powdermill Nature Reserve in southwestern Pennsylvania, about 1-hour drive East of Pittsburgh. Each blowdown was 3-6 ha (8-15 acres), within 3 km (2 miles) of each other. These blowdowns provide natural replicates to examine land snail response to habitat change. Given that some snail species are known to occur in forests and others in meadows, we might expect the snail species composition to shift when the wind turns part of a forest into a meadow.

Samples taken in 2016 showed differences in snail species community composition between the blowdown areas and the adjacent, intact forest. However, other statistical tests did not show differences that were significant, but they were nearly significant.

A good scientist should readily accept “no difference” when statistical results show that the differences are not significant. However, when the differences are tantalizingly close to significant, one might wonder whether “no difference” is real, or if a larger sample size might have demonstrated a significant difference.

So, we sampled again this year and took more samples. We are still processing the samples, so results are not in yet, but with the larger sample size, we will accept “no difference” if that is what the statistics tell us.

In the photo, Abbey is collecting leaf litter (containing snails) at the Laurel Run blowdown. The sample she collected contained 23 snails, of five species: Glyphyalinia indentata, Punctum minutissimum, Striatura ferrea, Striatura milium, and Zonitoides arboreus.

Timothy A. Pearce, PhD, is the Head of the Section of Mollusks and Abbey Hines is a Gallery Experience Presenter at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

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Box Turtle Time Capsule

box turtle

The year is 1974. Powdermill founder and Carnegie Museum of Natural History Director Dr. Graham Netting measures and marks a female box turtle found on the reserve and releases her. He estimates her age to be at least 16 years old. One wonders if he had any idea that during the 45 years since, Powdermill staff would continue to find her, alive and well.

box turtle
box turtle shell marked 22

We had the pleasure of encountering box turtle 22, as she is known, on August 29. The number etched into her bottom shell is still readily visible all these years later. She was last seen 8 years ago in 2011, and again 8 years before that, in 2003. In all, she has been recaptured 15 times since 1974! For a 61-year-old (at least), she is looking good and is as close to her 16-year-old weight as we’ve ever seen. Box turtles are known to live for over 100 years in captivity, but often much less in the wild due to predation and disease. Males typically travel more than females, covering distances of up to 10 km in 14 months!

data sheet about box turtle 22
data sheet about box turtle 22

Field stations like Powdermill are so valuable to biologists because of the knowledge that can be gained from these long-term datasets. Perhaps it will be another 8 years until we see her again, and who knows how many more decades she will continue to roam the forests of the reserve. After all, with an approximate birth year of 1958, she is about as old as Powdermill itself (founded in 1956).

Andrea Kautz is a Research Entomologist at Carnegie Museum of Natural History’s Powdermill Nature Reserve. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

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Lasius will Amaze-i-Us

Lasius workers tending a flock of aphids underground. Photo by Alex Wild.

Common Lasius ants tend aphids that live underground feeding on plant roots. They protect the herd of aphids from other ants, and move them to more productive roots if the plant dies back. Sometimes the future queen will pick up an aphid in her mandibles and carry it along on the mating flight, and place it on a good root in the wall of the first nest chamber to start a new herd of aphids.

At this time of year, Lasius have their mating flights. A warm day with some rain in the afternoon to soften the soil, and then a clear sky near sundown would be perfect. The ants will be in the top of the nest, awaiting the exact right moment. Somewhere between about 4:00 pm and 7:00 pm, when the atmosphere is just right, workers dig several passages to the surface, and usually the small and slender male ants emerge first, taking flight quickly. Future queens, much larger than the workers or males, and bearing large wings, emerge next and take flight. All the colonies in the landscape where the weather is appropriate may emerge in a time span as short as five or ten minutes.  We found dozens of colonies of two species (below) emerging in an area of our lawn about 20 feet by 40 feet.

Silver wings of many male Lasius neoniger are obvious as they prepare to take flight. Photo by Donna Wenzel.

The many gossamer wings may give the impression of smoke rising from the soil. Swallows, swifts, and other birds will fly in circles snapping up the winged ants. The queens will mate with one or a few males, who die promptly, and then the queens will dig into the moist soil and create a chamber for her new nest, maybe with an aphid she carried along the way to start her new colony.

But the life of Lasius ants is not all pastoral peace and harmony. Two different methods of parasitic attack have evolved where a queen of one species of Lasius will invade the nest of a different species of Lasius to take it over. In one of these methods, the parasitic queen releases citronella, a lemon-like odor that is pleasant to humans but communicates alarm to ants. The workers avoid the invading queen who works her way into the chamber where the host queen is. Quickly, the parasitic queen accumulates the odor of the host colony, and the workers will not recognize her as an alien usurper.

Here we see several large, winged Lasius claviger queens among many small workers, preparing to fly. These queens will parasitize mature colonies of other species, such as L. neoniger above. A few small, dark males are visible top, center. Photo by Donna Wenzel.

A different method used by some species is that the queen is very hairy or armored, and simply fights her way into the host nest. There, the invader may kill the host queen. By either method, the parasitic queen takes over the host nest, and the workers of the original colony, not knowing any better, spend their lives raising the offspring of the parasitic queen. As the original workers die out, the workers of the parasitic queen replace them until the colony is entirely of the parasitic species.

If you keep a sharp eye out at this time of year, you have a good chance of observing a mating flight of Lasius or another ant species, but you have to be in the right place at exactly the right time!

John Wenzel is the Director at Powdermill Nature Reserve, Carnegie Museum of Natural History’s environmental research center. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

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Brood VIII Birthday Bash

Photo by Andrea Kautz.

Millions upon millions of tiny cicada nymphs are being born. The periodical cicadas that emerged in our area (called “Brood VIII”) earlier this summer mated and laid eggs in the twigs of woody plants. Cicadas do not feed on twigs; they pierce the twigs on the underside, with a knife-like egg-laying tube called an ovipositor, and lay 10 to 20 eggs per incision. In the photo above, you can see the ovipositor behind the female’s back leg, inserted into the twig. At rest, the ovipositor would extend the length of the abdomen, so this one is about half embedded in the twig. In mid or late July, those eggs will hatch and the tiny nymphs will fall to the ground. They burrow down to find roots, where they will remain for 17 years, sucking plant juice.

Females can make dozens of separate incisions to lay hundreds of eggs in total. Because the cicadas need to leave their offspring on roots that will persist for 17 years, they prefer laying eggs in trees rather than shrubs, and tend to pick harder species, such as oaks, rather than softer woods like tulip poplar. Although they can feed on evergreen roots, the resinous nature of the sap in the twigs tends to suffocate the eggs, and they rarely lay eggs in evergreens. They can also feed on grass roots, and a big tree above a lawn becomes a popular egg-laying site. The many separate wounds on the twig interrupt water flow from the roots, and the twig often breaks or dies.

Photo by John Wenzel.

These damaged twigs are called “flagging” by cicada biologists, and they are a clear indicator of the density of females at a site.  This red maple over a lawn shows extensive flagging. A big tree may be supporting hundreds of thousands of eggs.

Photo by John Wenzel.

Despite the obvious damage to the tree, it appears that most trees do not suffer much unless they are little saplings. In fact, fruit tree farmers in the 1800s reported that their trees produced better crops the year after this natural pruning process.  Another benefit of the cicadas is that the millions of emergence holes open up the soil for air and water penetration and provide an avenue for nutrients at the top to pass into lower soil layers.  Although many people find the mass emergence of periodical cicadas to be annoying, they represent an inspiring and beneficial piece of our ecosystem, unique to eastern North America.

John Wenzel is the Director at Powdermill Nature Reserve, Carnegie Museum of Natural History’s environmental research center. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

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Honey Bees Hunt Bargains, Bumble Bees Go Gourmet

It is rewarding to receive questions and reports from people who turn to the staff at Powdermill Nature Reserve for information on nature in our area. Usually, we have a pretty good idea of what people are asking about, but once in a while visitors ask about something completely new to us. Last year, a visitor asked why he saw honey bees on his bird feeder in great numbers. The feeder was only stocked with bird seed. What were the bees doing?  We had no explanation. Recently, in the February 2019 issue of NY Conservationist, we read the answer. Mr. Gary Ennis provided a photo of the same phenomenon, and had the same question. According to beekeeper Bob Henke, during shipping and handling the seeds rub against each other and produce a fine powder similar to pollen, and the honey bees collect it as if it were pollen.

bees at a bird feeder
Photo credit: Gary Ennis.

But, why don’t we see other bees doing this?  Why are there no bumble bees on the feeder?  Bumble bees and other native bees sample the world one scout at a time, each bee making her own decisions. Researchers at Penn State showed that bumble bees monitor the nutritional value of the pollen they take, trying to keep an appropriate balance of protein versus lipids (fats, oils, and waxes.) If a certain plant produces pollen that has little lipid, then the bumble bee will favor pollen that is richer in lipids on future trips. This effort to balance their diet means that they specifically vary the pollen they harvest. It is as if they go to the grocery store and take a few items from the vegetable section, and a few from the dairy section, and a few from the bakery, creating a balanced plate on a daily basis.

On the other hand, honey bees are well-known for their ability to recruit to a good food source, and marshal large numbers of workers to harvest nectar or pollen. If an experienced scout finds a tree in bloom, she will recruit her sisters to that tree. They will go to that site directly without sampling other flowers on the way, and then return for another load, and another, and another.  This form of shopping is more like discovering that the grocery has potatoes on sale, and then buying 100 pounds of potatoes. Of course, a different scout will find a different resource, and she will recruit workers to harvest that in great numbers. As the weeks go by, the bees collect many different kinds of pollen, providing a broad selection for the nurse bees to feed the larvae. If we collect the separate loads of pollen from each returning bee: we see that each bee collected only one kind of pollen (all the same color), but different bees collected different pollen (many colors among the separate loads.)

pollen
Photo Credit: Jodi Gertz

Aside from the importance of recruiting, the scout honey bees also make some effort to balance their diet, particularly regarding the important fatty acids, omega-3 and omega-6. Work by Hebrew University in Jerusalem has shown that if these nutrients are not eaten in an appropriate ratio, the bees learn poorly and do not remember what they learn. For example, bees with adequate omega-3 in their diets are much better at learning to associate an odor with a food reward compared to bees with no omega-3. Further, the bees with good nutrition remember what they learned the next day, whereas those with a poor diet forget. We are only just appreciating what this means for bee pollination of large monoculture crops. When the 1.2 million acres of almonds are in bloom in California, about 3 million commercial bee hives are there to pollinate them for several weeks. During this time, almond pollen is all the bees will get. Almond pollen has almost no omega-3 fatty acids. When these poor bees are moved to other sites, how long will it take them to learn what flowers are good, and will they remember?

almond orchard in bloom

Thanks to NY Conservationist for allowing us to reprint the photo and retell the bird feeder story.

John Wenzel is the Director at Powdermill Nature Reserve, Carnegie Museum of Natural History’s environmental research center. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

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Another Reason to Love Ladybugs

mealy bugs on plant

The Marsh Machine at Powdermill is great for recycling the nature center’s wastewater. It’s also great for building up huge populations of pests, such as aphids, scales, and mealy bugs (Picture 1). These plant-feeding insects thrive in the warm greenhouse environment, free from the natural predators they would encounter in an outdoor setting.

lady bugs crawling out of a canvas bag

So what would be the logical solution to combatting these pests, which are highly destructive to the Marsh Machine plants that are working so hard to treat our wastewater? Bring the predators in, of course! The convergent ladybug (Hippodamia convergens), is a native predatory beetle that prefers just the types of insects that infest the Marsh Machine. We purchased 4,000 of these ladybugs (Picture 2) and have just released them into our greenhouse. The voracious predators immediately began their search and started feasting on a buffet of teeny bugs (Picture 3).

ladybug eating a mealy bug on a plant

According to our ladybug vendor, each adult ladybug can consume about 5,000 aphids in its lifetime! The adult females lay about 10-15 eggs a day, and the larvae that hatch out consume 50-60 aphids per day. At this rate, we anticipate our infestation will be under control in no time!

Note: While releasing ladybugs is an effective way to control greenhouse pests, releasing them outdoors generally results in the ladybugs flying away from the intended target, so keep this in mind when considering pest control options in your own backyard. Other options include eliminating the use of pesticides, which also kill the beneficial predators (and pollinators), and gardening with native plants, which are adapted to defend against native pests.

Andrea Kautz is a Research Entomologist at Carnegie Museum of Natural History’s Powdermill Nature Reserve. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.