• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar

Carnegie Museum of Natural History

One of the Four Carnegie Museums of Pittsburgh

  • Visit
    • Buy Tickets
    • Groups of 10 or More
    • Visitor Information
    • Events
    • Dining at the Museum
    • Celebrate at the Museum
    • Event Venue Rental
    • Shop
    • Powdermill Nature Reserve
    • Join & Give
  • Exhibitions
  • Learn
    • Field Trips
    • Educator Information
    • Programs at the Museum
    • Bring the Museum to You
    • Guided Programs FAQ
    • Programs Online
    • Climate and Rural Systems Partnership
    • We Are Nature Podcast
  • Research
    • Scientific Sections
    • Science Stories
    • Science Videos
    • Senior Science & Research Staff
    • Museum Library
    • Science Seminars
    • Scientific Publications
    • Specimen and Artifact Identification
  • About
    • Mission & Commitments
    • Directors Team
    • Museum History
  • Tickets
  • Shop

Cicadas

July 23, 2019 by wpengine

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.

Filed Under: Blog Tagged With: Cicadas, insects, Invertebrate Zoology, John Wenzel, Powdermill Nature Reserve

March 8, 2019 by wpengine

What are Seventeen-Year Cicadas and Why Does It Seem Like They Emerge More Than Once Every Seventeen Years?

two cicadas on a leaf

There are different broods of periodical cicadas.  Any given brood has adults emerging only once in 17 years and has a defined range of occurrence.  The brood we will see in Allegheny County this year (2019) is Brood VIII.  It is a brood with a relatively small distribution, occurring mainly in eastern Ohio, the panhandle of West Virginia, and about a dozen counties in southwestern and western Pennsylvania.

Adults will emerge in a couple of months (mid-May, but with climate change issues this is becoming less predictable; when the subsurface soil reaches 64 degrees Fahrenheit, emergence will begin), females will lay eggs, nymphs will hatch 6-10 weeks thereafter, and those nymphs will drop to the ground, burrow into the ground below deciduous trees, tap into the roots to syphon the plant juices, and remain underground for the next 17 years.  The adults of this brood will not be seen for 17 years, emerging again in 2036.

cicada on a leaf

Photo from Wikimedia Commons. 

Currently there are 12 broods of 17-year cicadas, each with a different aggregate distribution.  This means that in a 17-year period, adults will be emerging somewhere in 12 different years.  Some of these have a very small distribution; some have huge distributions.  For example, Brood X is nicknamed the Great Eastern Brood because it ranges from New York to Georgia, and west to Michigan. Brood X occurs over much of Pennsylvania, though not here in the southwest corner.  Its adults will emerge again in 2021 (and then 2038, etc.), but they are not related to or derived from the ones we will see this year. In a way, you can think of them as different clans or tribes that can’t interbreed or interact with one another because the adults are not in the same areas at the same time.

Of the 12 broods, 8 of them occur in Pennsylvania as a whole, though mostly to the east.  Here in the southwest, we get only 3 broods.  This means here in southwestern Pennsylvania, we will normally see adults emerging during 3 years out of 17.  Brood VIII, already mentioned, will be out this year and again in 2036.  Brood VII we saw here last year (2018), and it will be out again in 2035.  Both of these have been found in Allegheny County.  Brood V, last seen in 2016 and due again in 2033, has not officially been recorded from Allegheny County, but since it is known from nearby Greene, Washington, Westmoreland, and Fayette Counties, it is most likely here.

And, to be clear: there are other kinds of cicadas that come out every year.  These are usually called Annual Cicadas.  They don’t aggregate in big swarms, so there is just one here, one there.  Nymphs are underground only a year or two, so there are adults every year.  And they are active later in the season, mostly July-September rather than May-June. These are the solitary ones you hear singing in a tree in late summer.

Bob Davidson is Collection Manager of Invertebrate Zoology at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

Filed Under: Blog Tagged With: Bob Davidson, Cicadas, Invertebrate Zoology, Robert Davidson

sidebar

About

  • Mission & Commitments
  • Directors Team
  • Museum History

Get Involved

  • Volunteer
  • Membership
  • Carnegie Discoverers
  • Donate
  • Employment
  • Events

Bring a Group

  • Groups of 10 or More
  • Birthday Parties at the Museum
  • Field Trips

Powdermill

  • Powdermill Nature Reserve
  • Powdermill Field Trips
  • Powdermill Staff
  • Research at Powdermill

More Information

  • Image Permission Requests
  • Science Stories
  • Accessibility
  • Shopping Cart
  • Contact
  • Visitor Policies
One of the Four Carnegie Museums | © Carnegie Institute | Privacy Policy | Terms of Use | Accessibility
Rad works here logo