Tuesday, May 11, 2004

Marlatt sings to Dylan:

I went to a lecture today by four researchers on cicadas. So did NBC, CNN, WTOP-radio, and even Animal Planet. It was quite a frenzy. Two hours of scientific talk followed by questions from reporters. Can I scoop them with this post?

A frenzy much like it is starting to be with the cicadas themselves, because Brood X started their emergence this weekend.

Much of the basic facts you can find elsewhere, or you have probably read in the papers lately, since there have been so many articles. Here are the points I found interesting in their talks that I had not heard elsewhere:

Keith Clay, Indiana University at Bloomington
Clay and his team are investigating what preferences cicadas have for egg-laying sites (tree species, density, etc.), and how the insect density affects tree response, and the interactions between forest succession and cicada populations. Clay looks at patterns of interaction between the microbial, plant, and human worlds. Clay's website.
  • Brood X is the largest insect emergence in the world
  • It occurs largely in deciduous forests
  • Apart from two very small patches in Canada, it is within the lower 48 only
  • Different species exist within the same brood (!)
  • There are documented cases of densities of over 4000 nymphs per hectare
  • Cicadas are probably still recovering from a population collapse caused by the deforestation of the Eastern U.S. in the 19th century
  • Given their preference for calling, mating, and laying eggs on forest edges or regrowth areas (and NOT in deep forest), they will probably exceed historical populations given current land cover patterns and forest fragmentation
  • Studies on Brood XXIII showed the preferred tree for egg-laying to be the Elm, and the least preferred to be the Persimmon
  • Egg-laying will cause scarring on newly grown twigs
  • They actually can harm very young saplings, but not older trees


James Speer, Indiana State University
Speer and his team are looking at how cicadas affect tree growth during the different stages of their cycle, from the oviposition (egg-laying) by scarring or "tagging" tree branches, to the long underground feeding, to the effect on the trees of the emergence and release from parasite burden. They do this mainly by looking at tree rings, and correlating periods of good and bad growth with known cicada emergences. To date they have looked at Red Maples, but this summer they plan to broaden the study to many other species. ISU Dendro lab page.

  • Females lay about 20 eggs per scar on a twig, and lay about 600 total
  • The visual impact of the emergence and egg-laying on a forest will be large, but the tree-rings tell a different story - most 'damage' is done in the nymphal stages feeding underground, and it increases until emergence, when the trees suddenly surge because they have no cicada nymphs siphoning off their roots
  • There is a characteristic pattern in the tree rings that they beleive is due to cicadas, and they plan to go back to the dendrochronological record to see if they can see other great emergences far in the past (for example, in a still living 250 year-old Oak, and further back in the dated tree-ring record).


John Odland, Indiana University
Odland is an economic geographer, and his interest with cicadas is looking at how human modification of the landscape around us is affecting the cicada population (among other animals). Odland's web site.

  • The movement of biomass is significant
  • 130 nymphs per square meter is a 'moderate' concentration
  • It has to get up to 35C before the males can sing effectively (therefore their preference for forest edges)
  • The males congregate, perhaps to louden their collective call (?)
  • Young trees of long lived species are favored (for repeat generations?)
  • Humans have created a lot of forest edge, through patchy reforestation, and through penetrative development of forested lands
  • Because of the extensive clearing in the 1800's there was concern in the 1902 Brood X emergence that cicadas would go extinct
  • ...but they were still plentiful enough that the 1902 University of Indiana graduation had to be cancelled and moved indoors, since no one would have been able to hear any of the speakers
  • This will probably be a bad fishing season, since fish will be stuffed to the gills with cicadas, and not interested in your lure
  • Cherry trees with tagging scars will ooze sap that is laced with cyanide (from the cherry, not the cicadas). Would one call this a "sappurating" wound?


Christine Simon, University of Connecticut
Simon's group looks at the evolution of cicadas using tools like mDNA, and looks at questions like Why are there separate broods, and how did they evolve? Why are there 13- and 17-year broods? Why do some 13-year species appear 4 years late (with the 17's), and some 17's appear 4 years early (with the 13's)? Simon has a really nice web site on cicada research.

  • There is a genetically separate 17-year group that seems to have successfully shifted to a 13 year periodicity because it coincided with a 13 year hatch, and was protected from being wiped out
  • There seems to be a cyclic connection between the broods:

XIV ---> X ---> VI ---> II

| | | |

XIII IX V I

| |

XII VIII

| |

XI VII


Where there can be either four year differences in emergence year (horizontal), or single year differences (vertical)

  • Where the new 13's overlap with the old 13's in the same brood, they sing quite differently - this difference drops off as you go away from the overlap zone
  • We are probably seeing speciation in action here, as obvious as it will get
  • When surveying the public about cicada emergence, they ask the question "Have you heard any flying saucers lately?"
  • They are planning to put micro-transmitters on cicadas to track how far they actually travel before laying their eggs (since they have the reputation as clumsy flyers, it's not clear how effectively they 'spread' into new territory)
  • Other long-lived insects do exist - Asian beetles have hatched in imported furinture more than 50 years old, and some moths can go into diapause (dormant) for up to 20 years
  • Bob Dylan was in Princeton, New Jersey during the 1970 Brood X emergence, and was so impressed by the racket that he wrote the song "The Day of the Locusts".
  • There are cicadas in Fiji and the U.S. Southwest that may also be periodic - but there is so little data on them that we can't be sure
  • The Fijians make necklaces out of them


Other notes I cam across while doing this:

  • Brood X will affect the mid-West much more than Virginia
  • Brood II's 1996 emergence in Virginia was heavier than what is expected out of Brood X
  • Brood X is heaviest in southern Indiana, Kentucky and Ohio
  • A USDA entomologist, Charles Marlatt, came up with the Roman numerals for the broods
  • They simply indicate the different successive years they emerged when he started counting
  • ...hmm. You could easily figure out when he started counting, methinks. Bonus Mensa question: when will they again emerge in order?
  • A visiting Swedish minister wrote home about an emergence in 1715. It was Brood X!


Where were you in the summer of 1987? 1970? 1953? 1936? 1919? 1902?

And where will you be in 2012?

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