22-31 August 2007

Installment #369---
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In last week's discussion about Dog Days of August, we intentionally avoided mention of an insect whose name is derived from that time of year, i.e., the Dog-day Cicada. This bug-eyed creature--which measures two inches from head to tip of folded wing--reminds us when Dog Days have arrived, buzzing incessantly dawn to dusk from midsummer through Labor Day, and sometimes after that. We've written about Dog-day Cicadas in the past, but our story was always incomplete; even though we have tons of adults at Hilton Pond Center, we'd never found a live nymph until this week, so we wanted to devote an entire new installment to this noisy denizen of summer's hottest days.

All text & photos © Hilton Pond Center

One evening in stifling summer heat, we walked out to close two mist nets we erect at the old farmhouse throughout August to catch Ruby-throated Hummingbirds. With daytime temperatures this month near or even exceeding 100 degrees, it was important to check the nets every ten minutes or so to make sure any snared hummers were not stressed by heat. On our after-supper net check--when light was waning but temps were still in the upper 90s--we noticed something moving on the ground in heavy shade beneath an Eastern Red Cedar tree just off the back deck. On closer examination we found it to be a Dog-day Cicada in its nymphal stage, slowly emerging from a hole in earth that had been its home for the past 2-4 years.

Broods of our southern Dog-day Cicadas have much shorter life cycles than the more famous Periodical Cicadas (above), which are black with orange-red eyes and emerge predictably but dramatically every 13 or 17 years--a heckuva long time to spend maturing underground. Periodical Cicadas are far more common in the northeastern and midwestern states, but Brood VI of the 17-year cicada did have an emergence in the Carolinas and Georgia in 2000, and Brood XIX of the 13-year group is next due in 2011. These Periodical Cicadas, Magicicada spp.--emerge in such huge numbers that congregations of adults can break tree branches. One summer when we worked at Hawk Mountain Sanctuary in Pennsylvania, Periodical Cicadas were so plentiful it was impossible to pass through the woods without crunching dozens of them underfoot.

Although they don't erupt in plague-like numbers like their more northerly cousins, Dog-day Cicadas (above) are common throughout the South. There are several species--the one here at Hilton Pond Center is Tibicen canicularis--but all are some shade of green with bulging brownish-blackish-greenish eyes (below).

In addition to these compound eyes used for image detection, there are three golden jewel-like ocelli in the center of the cicada's forehead (above); each of these single-faceted "simple eyes" apparently detects light and dark--which may be why it's so difficult to sneak up on an adult Dog-day Cicada. Any shadowy movement that falls on the its ocelli prompts the cicada to fly off with considerable speed that belies its blunt, non-aerodynamic shape. Just below the ocelli are two bristle-like antenna that could be touch sensors but may also detect other outside stimuli.

In summer, biological clocks ticking in the oldest Dog-day Cicada nymphs tell them it's time to give up their subterranean life and become adults--a transition that requires an amazing metamorphosis. The nymph (above) is a hunchbacked creature with vestigial wings and short, pincer-like forelegs adapted for digging through the soil to get close to roots of trees and shrubs. Its eyes, which can't be of much use underground, are bulbous like those of an adult, and it already has those short, bristly antennae. The mouth is a long, tubular sheath that surrounds four needle-like stylets the nymph uses like a hypodermic needle, plunging them into the vascular tissue of the tree root and extracting nutritious sap.

On cue, and usually at dusk or later, the nearly mature nymph crawls from the earthen chamber in which it has spent its lifetime and makes for the nearest vertical object--be it tree, fence post, or building wall. After ascending this structure, it slowly cracks out of its "shell" and changes from a short, rotund, flightless immature into the elongated and winged adult Dog-day Cicada. Left behind is a translucent exoskeleton (below) that is a perfect mold of the now-departed cicada nymph.

If it has metamorphosed on an inanimate object, the adult cicada flies to a nearby tree, where it proceeds into outer or topmost branches. There the males give forth with a droning chorus, their joined voices providing an easier-to-find target for females on the prowl for mates. The compatible pair copulates, after which the female finds an appropriate small branch, makes a small slit through the bark with her sharp ovipositor, and lays a single egg within the tree's living tissue. She repeats this act until her eggs are done and then--like the male--dies within two weeks after emergence. The mates' genes live on, however, in their offspring, which hatch and spend a few weeks munching within the twig before falling to the ground, where first-stage nymphs enter the soil for 2-4 years of growth and development.

Here in York County SC we set a record for the hottest August in history--daytime highs reached at least 90 degrees for 31 consecutive days--and also officially the driest, with less than half an inch of total precipitation for the entire month. It was a tad cooler here at Hilton Pond Center and an isolated thunderstorm did give us 1.3" of rain one day, but there's little doubt we've just been through the doggiest Dog Days we've ever experienced. Those Dog Days are technically over by now, but male Dog-day Cicadas are still buzzing away, trying to win over females with that never-ended song that always reminds us of Piedmont summer.

All text & photos © Hilton Pond Center

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Be sure to scroll down for an account of all
birds banded or recaptured during the period,
plus other nature notes of interest.

Thanks to the following fine folks for recent gifts in support of Hilton Pond Center for Piedmont Natural History and/or Operation RubyThroat: The Hummingbird Project. Your tax-deductible contributions allow us to continue writing, photographing, and sharing "This Week at Hilton Pond." (Please see Support if you'd like to make a gift of your own.)

  • Christopher Baldwin
  • Cori Dulmage
  • Charlotte/Mecklenburg Park & Recreation, Chirp 'n Chatter Backyard Nature Store, Dr. JB's Hummingbird Feeders & Longhorn Steak House (sponsors of recent "Hummingbird Mornings" at Reedy Creek Nature Preserve, Charlotte NC)
  • Numerous anonymous contributors at Reedy Creek
  • Additional anonymous contributors via quarterly disbursement from iGive (see below)
  • South Carolina Midlands Master Gardeners Association (speaker's fee and donation)


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"This Week at Hilton Pond" is written & photographed
by Bill Hilton Jr., executive director of
Hilton Pond Center for Piedmont Natural History.

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21-31 August 2007

Ruby-throated Hummingbird--31
American Goldfinch--1
Northern Cardinal--3
Scarlet Tanager--1
(hatch year male)
Eastern Towhee--1

* = New species for 2007

5 species
37 individuals

35 species
928 individuals

(since 28 June 1982)
124 species
49,011 individuals

(with original banding date, sex, and current age)

Ruby-throated Hummingbird (1)
09/06/06--2nd year male

--Now that our Hummingbird Mornings presentations are over for 2007, we can report we reached more than 2,000 hummingbird enthusiasts in four states during our lectures, workshops, and banding demonstrations. If your organization or business would like to sponsor a day or weekend in 2008, please see Hummingbird Mornings and contact us at EDUCATION.

--This week we banded our 49,000th bird at Hilton Pond Center since 1982, a female Ruby-throated Hummingbird.

All text & photos © Hilton Pond Center


--We're often asked about predators of Ruby-throated Hummingbirds, and there aren't many. We've never personally seen a predator take a hummer, but that almost changed this week when we observed an apparent juvenile RTHU investigating a Pickerelweed flower stalk (above) in the water garden just outside our office window at Hilton Pond Center. As the hummer hovered, a dark mass shot straight up out of the pond; we recognized it as a large Green Frog, Rana clamitans. The hummer easily avoided the flying leap of the frog--which fell empty-mouthed back into the water--but there ARE a few references in the scientific literature to closely related Bullfrogs, Rana catesbeiana, occasionally capturing less agile hummers.

--A hatch-year male Scarlet Tanager netted on 28 Aug was quite early for Hilton Pond Center. This species--which does not bred in this part of the Carolina Piedmont--usually doesn't show up until mid- to late September, although we did get one in late Jul 1994.

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