Season 4, Episode 8: Brood 14
Crows are attacking people in a town in Tennessee, and the US government calls on NorBAC to investigate. As the attacks spread further northward, NorBAC discovers that the crows have been eating the most recently emerged brood of insects called cicadas. The cicada larvae had been underground for 17 years, sucking on the roots of elm trees, which had been treated with pesticides to prevent Dutch Elm Disease. The pesticides contained copper sulfate, which accumulated in the bugs, and appeared to affect the brains of the crows that ate them, making them psychotic.
 Image provided courtesy of Shaftesbury Films. |
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Carlos looks for shelter as a murder of angry crows descends. |
CAN CROWS BECOME VIOLENT FROM A DIET OF COPPER SULFATE-LACED CICADAS?
When do cicadas emerge?
Periodical cicadas, also called magicicadas, live underground as larvae for many years before becoming adults and emerging above ground. During their time underground, they feed by sucking fluids from tree roots. Seven different species of magicicada are known in North America: four with a 13-year cycle from birth to emergence as an adult and three with a 17-year cycle.
The cicadas are divided into thirty groups, or "broods", according to the year they emerge from the ground. Brood XIV, which plays an important role in this episode, has a 17-year cycle and is expected to come up in late April or May 2008 in several US states. Most of these cicadas will emerge in Kentucky and Pennsylvania, but some other states, including Tennessee and North Carolina, will also see cicadas in 2008.
 Image provided courtesy of Shaftesbury Films. |
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Mayko explains the life cycle of cicadas to the NorBAC team. |
What is Dutch Elm Disease and how is it prevented?
Dutch Elm Disease is caused by the fungus Ophiostoma ulmi, which blocks water transport within a tree, causing it to die. O. ulmi was first identified in The Netherlands in 1921, giving Dutch Elm Disease its name. In 1928, the fungus reached North America by way of imported lumber, and has since destroyed about half of the elm trees on the continent. The major cause for the spread of the fungus is the elm bark beetle (Scolytus multistriatus), which feeds on elm trees and carries O. ulmi spores as it moves from diseased trees to healthy trees.
To stop the spread of Dutch Elm Disease, the US government initially sprayed all areas with elm trees with a synthetic pesticide called dichloro-diphenyl-trichloroethane, or DDT, to kill the elm bark beetle. With the beetles gone, the spread of disease was slowed down. However, after several years it became clear that DDT also affected the bird populations in the sprayed areas, and that there might be some adverse effects in humans: For example, some studies have linked childhood exposure to DDT to breast cancer in adulthood. The chemical was banned in the US, in 1972, but is still recommended for use in tropical countries to fight the spread of malaria by killing mosquitoes. There, the health risk of malaria far outweighs the environmental and health risks of DDT.
Nowadays, Dutch Elm Disease is treated by attacking the fungus itself, rather than the beetles; fungicides containing a mix of chemicals, including copper sulfate, are injected directly into the tree roots.
Is copper sulfate toxic to crows or cicadas?
Birds have a very high tolerance for copper sulfate compared to other species. The compound is very toxic in fish and other aquatic organisms, though, and in high doses it can cause liver damage in other species as well. Mammals are more affected by copper than birds, so the moles we see in this episode would probably be more ill from a diet of copper-containing cicadas than the crows. The effect of copper sulfate on cicadas is not known, but a study of other insects found that root weevil larvae, which feed on plant roots much like cicada larvae do, didn't develop into adults if they were exposed to copper sulfate.
Do increased copper levels cause schizophrenia?
Our bodies need small amounts of copper to function. For example, brain chemistry is in part regulated by proteins that only work when they're bound to copper. Excess amounts of copper in the body are secreted in bile and cleared out of the body. If there is too much copper for the body to handle, the first symptom will be liver damage, as mentioned above. This happens not only in cases of copper poisoning, but also in Wilson's disease, a genetic condition in which copper is not properly secreted. Other symptoms of Wilson's disease include loss of memory, clumsiness, depression, and in rare cases a type of psychosis that resembles schizophrenia.
Schizophrenia is characterized by hallucinations and delusions -- it's not the same as multiple personality disorder. Many people who have been diagnosed with a form of schizophrenia have increased levels of copper in their blood, but it's not known whether this is a symptom or the cause of schizophrenia.
So?
It's not likely that copper sulfate from cicadas would cause crows to suddenly become violent and attack. Cicadas do eat sap from tree roots, and will probably take up any water-soluble chemicals that come with it, such as copper sulfate from fungicides, but it's not known whether the larvae would develop into adults and/or survive if their levels of copper sulfate got too high. Even if the cicadas were able to mature with high levels of copper sulfate in their bodies, the most likely effect this would have on any birds that prey on them is liver disease from copper poisoning.
DID YOU KNOW?
While investigating the cause of the crow attacks in Tennessee, Carlos finds that the moles in the area contained high levels of formaldehyde. The formaldehyde had leaked into the ground from the local cemetery. Formaldehyde is a chemical used in embalming fluid to temporarily preserve bodies so family members and friends of the deceased can mourn and view the body for a few days before it's buried. Without embalming, the bodies would degrade and rot too quickly. However, inhalation of formaldehyde been linked to cancer, and there have been some concerns about the environmental and health effects of burying formaldehyde-embalmed bodies. Those concerned have proposed "green burials" in which bodies are buried in without embalming and in biodegradable caskets. There are only four such green funeral sites in North America, but it's more popular in the UK.
-- Eva Amsen
Want to read and learn more?
The website Cicada Mania has regular updates on cicada emergences, including a section on Brood XIV:
http://www.cicadamania.com/cicadas/category/brood-xiv/
Read an article about fungicide injection to prevent Dutch Elm Disease:
http://www.na.fs.fed.us/spfo/pubs/misc/ded/ded.htm
To learn how the body handles copper, read about Wilson's disease, where copper isn't properly processed:
http://en.wikipedia.org/wiki/Wilson%27s_disease
Read an article about green burials:
http://www.thestar.com/article/174974
