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Return to Texas Entomology - Compiled by Mike Quinn
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July Records north of the Green-June Line
June Records north of the Red Line
December through May US Records
Blue Records - March through July 2004 - Year of a major outbreak
The Black Witch Moth (Ascalapha odorata) is a large brown bat-like moth that annually emigrates north across North America with usually a few individuals being recorded in Canada each year.
The standard method of plotting a species' range is to plot all the records as the Moth Photographers Group (MPG) did for the Black Witch Moth. The MPG map shows a fairly even distribution of the moth with a higher density in the south from CA to TX and FL. Some clustering further north, such as in CO, KY and OH, may be due in part to increased survey efforts.
To tease out more information of a migratory species, one again usually maps all records for the species but color codes the records by date as Journey North did by mapping the Monarch Spring 2012 Migration by two week intervals.
to these normal mapping protocols, I only mapped the records that
occurred north of the previous month(s)'s records. This methodology cuts
down drastically on the over 500
that I would have been obliged to plot using traditional methods.
I used Blue Markers to show the tremenous number of records from 2004 when this species had a major outbreak. I was able to greatly increase the number of records I received as I worked for Texas Parks and Wildlife at the time and we issued a June 28th press release requesting BWM reports.
Results and Discussion
The onset of the BWM emigration out of Mexico begins in June of each year and appears to be very strongly tied to the start of the rainy season in Mexico which begins in May and June. While Monarchs cross the Rio Grande starting in March and take two months to reach Canada, Black Witches have been recorded reaching Maine by June 9th, Door Co. Wisconsin by June 16th and Manatoba by June 28th. By the end of June, Black Witch Moths have been recorded in 19 states and two Canadian provinces.
The by-month mapping methodology employed here documents the moth's very significant migration out of Mexico and into the central US and also indicates that almost no Black Witch Moths migrate north out of Florida in June.
The Blue Markers (2004) show a more western distribution, CA west to LA and NE, particularly for June than the Green-June Markers (all yrs except 2004) which primarily range from the Rocky Mountains east. However, the records north of the Green-June Line do show an overall more westerly distribution in line with the 2004 outbreak data. This western distribution is certainly more pronounced than the data show given the many times fewer potential observers living in western North America than in the east.
Nearly all the BWM data I have are from
random observations except the following two data sets from locations
on the Texas coast north of Corpus Christi.In May and June of 2004, Ray
Little conducted regular 25 mile long surveys of Matagorda Island, Calhoun Co.
on a 4-wheeler looking for sea turtle nests. He also kept track of BWMs
he saw which flew up from the beached sargassum as he drove past. None
were see on surveys prior to May 30. Very similar numbers were reported
by the Aransas Pass Lighthouse keepers. The keepers reportedmoths perched under north
facing eaves of one of the buildings just south of Matagorda Is. in Aransas Co. during 2004 and 2005.
Aransas Pass Light Station on
Harbor Island, Aransas Co.
Other significant numbers along the Gulf Coast suggesting peak moth passage roughly in line with the numbers above include "dozens" reported on June 15, 2004 further up the coast on Grand Isle in southeast coastal Louisiana by Wayne Keller and a report of "fairly high numbers" on July 2, 2005 at Galveston Island State Park southeast of Houston.
|Aug. 8, 2000
||"at least 50"||near Patagonia, southeast Arizona
||sheltering in an old shack|
|Aug. 12, 2004 - OCR
||37 separate reports
||San Deigo, Orange, and LA counties in so. Calif.
||triggered by Orange County Register article
|Aug. 26, 2012||6
||Beeville, Bee Co., south Texas
||under 8 x 15 ft covered poarch
|Aug. 27, 2005||51||Bentsen-RGV
State Park, south Texas
||under the pavilion roof|
|Sept 1, 2005
||up to 72||Bentsen-RGV State Park, south Texas||sheltering under the pavilion roof.|