24-30 Jun 2010
Installment #477---Visitor #count internet traffic

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Join fellow birders & educators as citizen scientists on 2011 Operation RubyThroat expeditions to observe, capture & band hummingbirds in Belize, Nicaragua, Guatemala & Costa Rica. No experience necessary! Alumni of selected Holbrook trips receive a $150 discount. (Click on logo at left for more info.)

All text & photos © Hilton Pond Center


Sometime during the mid-1990s a tall purplish-pink wildflower appeared on its own along the banks of Hilton Pond and we were very pleased to see it. The plant was Swamp Milkweed, Asclepias incarnata (above), a native species that grows in the U.S. and Canada in all states and provinces except on the Pacific Coast. As its common name suggests, Swamp Milkweed does best in moist soil and can even thrive in riparian habitats with roots submerged. Like all milkweeds its ornate flowers are pleasing to the eye, but the real reason we were happy to find it at Hilton Pond Center was because it's a host plant for Monarch butterfly larvae (right)--among the most colorful of all caterpillars. Our Swamp Milkweed colony expanded through the years--flowering profusely each July and propagating itself with winged, windblown seeds--and a few years ago we finally started seeing Monarch caterpillars feeding on milkweed foliage. In 2009, however, our Swamp Milkweeds produced almost no blossoms and hosted no Monarchs and we couldn't figure out why. Now we think we have at least part of the answer.

All text & photos © Hilton Pond Center

This week as we checked our Swamp Milkweed crop for flowers and Monarch larvae we found neither, but atop one stalk perched a nearly half-inch-long beetle in brilliant Halloween colors (above). Considering the plant it was on, we hadn't much doubt about the insect's identity: It was a Swamp Milkweed Leaf Beetle, Labidomera clivicollis, and it appeared to be chewing on unopened flower buds.

Insect observers won't be surprised the Swamp Milkweed Leaf Beetle--shall we call it SMLB for short even though it does occur on other milkweed species?--is in the Leaf Beetle Family (Chrysomelidae). This is a huge coleopteran family with more than 2,500 genera and 35,000 named species worldwide, including such economically important species as Colorado Potato Beetle (right), Cereal Leaf Beetle, and Asparagus Beetle--plus various Flea Beetles that eat both desirable garden plants and unwanted weeds. Some chrysomelid beetles resemble Ladybird Beetles (Coccinelidae), but most--not all--the latter are beneficial predators of other insect larvae and don't dine on flora like SMLBs and their relatives.

As do other beetles, SMLBs undergo complete metamorphosis (egg-larva-pupa-adult), with the larva molting through four "instar" stages--each about twice the size of the one preceding. The last instar drops earthward and burrows into the soil where it pupates. In the Carolinas there apparently are at least two generations, with noticeably smaller individuals being produced during poor environmental conditions such as drought. Some adult SMLBs overwinter hidden in leaf litter or other suitable spots.

All text & photos © Hilton Pond Center

The morning after we spotted our adult SMLB on Swamp Milkweed we returned with a 10x hand lens to see if we could locate eggs or immatures. The adult was on an adjoining flower stalk but we couldn't find any eggs, perhaps because around these parts they're usually laid in late May or early June. We did manage to locate baby beetles in a couple of different sizes. The nearly spherical one in the photo above was a little less than a quarter-inch in length and probably a third instar, while the tiny backlit one below likely was a first instar and only about 1/8" long. The black bodies in the image below are even tinier deposits of frass. (NOTE: We worked hard to keep the top photo of the adult beetle and those of the two instars roughly to scale.)

All text & photos © Hilton Pond Center

Entomologists have determined Swamp Milkweed Leaf Beetles may utilize several forms of cannibalism, with newly hatched offspring eating their siblings' eggs, older larvae eating eggs of unrelated SMLBs, and adult female SMLBs eating egg clutches from other females. It's curious an insect that's normally phytophagous--plant-eating--engages so readily in cannibalism. However, this behavior not only provides immediate nutrition, it also helps eliminate later competition for food and reduces population densities such that predators on SMLB larvae--mostly spiders or adult and larval flies--have a harder time finding them.

All text & photos © Hilton Pond Center

The adult Swamp Milkweed Leaf Beetle stayed within one ten-stalk milkweed colony for at least the last three days of June, wandering from--and dining upon--one flower head after another. We're guessing thanks to the voracious appetites of it and numerous SMLB instars our Swamp Milkweed blossoms will be fewer again this year at Hilton Pond Center.

All text & photos © Hilton Pond Center

TECH NOTES: Swamp Milkweed Leaf Beetle photos above were made with a Canon 100mm f/2.8 Macro Lens mounted on a Canon 7D with built-in flash and a Canon 12mm Extension Tube II. A Canon 25mm Extension Tube II was used for the 1st instar image (no flash).

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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. You can also contribute by ordering an Operation RubyThroat T-shirt.)

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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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24-30 June 2010

American Goldfinch--1
House Finch--18

* = New species for 2010

2 species
19 individuals

32 species
555 individuals
Ruby-throated Hummingbirds
(since 28 June 1982, during which time 170 species have been observed on or over the property)
124 species (29-yr avg = 67.6)
54,197 individuals
(29-yr avg = 1,868.9)

(with original banding date, sex, and current age)
None this week

Operation RubyThroat has teamed with EarthTrek so citizen scientists--like YOU--can contribute observations about hummingbird migration and nesting behavior. Membership is free for this great new opportunity to help increase scientific understanding of Ruby-throated Hummingbirds. Data entry forms for 2010 are on-line, so please register today at EarthTrek.

NOW is the time to report your 2010 RTHU spring arrival dates for the U.S. & Canada, and spring departure dates for Mexico & Central America.
Please participate.

--This wasn't the hottest June on record for York SC and
Hilton Pond Center--five others in more than a century of recorded weather history were hotter--but 2010 it WAS the first time June ever had 18 consecutive days on which the thermometer went above 90 degrees. (And it DID get up to 98 on the 27th.) Such stifling heat is to be expected 'round these parts in August, but we expect June in the South to be a little more civil while we gradually get used to the heat of summer.

--With bird welfare in mind, we elected not to operate mist nets in the heat and humidity during the most recent seven-day period, lest our netted captives suffer from hyperthermia. We did run a couple of hanging traps baited with sunflower seeds and were quick to remove recently fledged House Finches--and one adult male American Goldfinch--that entered during the week.

--Ruby-throated Hummingbirds continue to be almost non-existent at the Center, with only a few feeder visits per day and none banded since 1 Jun. Many correspondents report similar low numbers at many U.S. sites, so we hope what we tell them--to be patient until numbers increase as this year's fledglings start appearing--will really happen in 2010.

--June ended with a torrential mid-afternoon thunderstorm on the 30th. We welcomed the one-inch downpour that fell on Hilton Pond, knowing behind it there would be some sort of cool front that would lower temp at least a few degrees.

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Hilton Pond Center for Piedmont Natural History is a non-profit research & education organization in York, South Carolina USA; phone (803) 684-5852. Directed by Bill Hilton Jr., aka The Piedmont Naturalist, it is the parent organization for Operation RubyThroat. Contents of this Web site--including all articles and photos--may NOT be duplicated, modified, or used in any way except with the express written permission of Hilton Pond Center. All rights reserved worldwide. To obtain permission for use or for further assistance on accessing this Web site, contact the Webmaster.

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