DISTRIBUTION:

Pachysphinx occidentalis occidentalis, the Big Poplar Sphinx (Wing span: 5 1/8 - 5 7/8 inches (13 - 15 cm)), flies in riparian areas and suburbs from Alberta and North Dakota west to eastern Washington; south to Texas, Arizona, southern California, and Baja California Norte.

Pachysphinx occidentalis female, Silver City, New Mexico,
August 6, 2007, courtesy of David R. Furnas.

There are two color forms: the upperside of the forewings is yellow brown in the pale form and dark gray in the dark form. Lines and bands are well-defined. The upperside of the hindwing has a crimson patch covering varying amounts of the wing, and two dark lines which do not form a distinct triangle.

Pachysphinx occidentalis male, courtesy of Martin Jagelka

Visit Pachysphinx occidentalis, Payson, Gila County, Arizona, July 24, 2009, courtesy of Lauren Paterson.

FLIGHT TIMES:

Male and female Pachysphinx occidentalis moths come to lights as two broods in southern Arizona from May-September, and as one brood northward from June-August. Nick Richter of Lake Forest, Orange County, southern California, reports his second brood larvae have begun pupating, November 29, 2012.

The adults do not nectar at flowers.

Many thanks to Jeanne Marker who provides this "early bird" surprise.

Pachysphinx occidentalis, south of Tucson, Pima County, Arizona,
March 19, 2015, courtesy of Jeanne Marker.

Jeanne was surprised to see this moth so early (March 19-20, 2015), and I (Bill Oehlke) indicated to her, "Usually in southern states they do not begin to appear until May. If pupation was in soil near south side of a home where soil would warm faster than in a much more wooded area, and you have had a bout of relatively warm weather, those factors may have triggered the early development and eclosion. Thanks for thinking of me."

Pachysphinx occidentalis, Washoe Valley, Washoe County, Nevada,
June 20, 2012, courtesy of Terri McLaughlin.

ECLOSION:

Little is known about the eclosions of the earth pupators, but many believe pupae wiggle toward the surface just prior to emergence.

Pachysphinx occidentalis female, courtesy of Martin Jagelka

SCENTING AND MATING:

Female Pachysphinx occidentalis extend a scent gland from the posterior of the abdomen to lure in the night flying males whose large claspers are frequently wide open as they fly in to lights around midnight.

Many thanks to Jennifer Rosta who sends the following images of Pachysphinx occidentalis. The female emerged from a subterranean chamber on April 5, and climbed up the side of the house. That night she called in a male via a pheromone scent released into night sky, and Jennifer took the picture of both male and female in copula on April 6.

The pair separated on the night of April 6 and this morning, April 7, 2015, only the famale remains. If she does not get eaten by a bird or other predator, she will fly away, under cover of darkness, to disperse the 200-300 translucent-green (more toward yellow) egg-payload she is carrying in her swollen abdomen. She will lay the eggs in small groups of 4-8 on poplar or willow foliage over the next 5-7 nights.

Pachysphinx occidentalis female, Phelan, San Bernardino County, California,
April 5, 2015, courtesy of Jennifer Rosta.

Pachysphinx occidentalis in copula, Phelan, San Bernardino County, California,
April 6, 2015, courtesy of Jennifer Rosta.

Pachysphinx occidentalis post copula, Phelan, San Bernardino County, California,
April 7, 2015, courtesy of Jennifer Rosta.

Pachysphinx occidentalis swollen abdomen, Phelan, San Bernardino County, California,
April 7, 2015, courtesy of Jennifer Rosta.

EGGS, LARVAE, PUPAE: Pachysphinx occidentalis eggs are quite large and a translucent pale green, more towards pale yellow. Larvae feed on cottonwood and poplar (Populus) and willow (Salix). Pachysphinx occidentalis male, courtesy of Martin Jagelka I have not reared P. occidentalis, but I have reared a very close relative, P. modesta, many times on Prince Edward Island. I suspect the life histories are probably very similar. Here are notes for modesta: Eggs are fertilized as they are deposited while they are being coated with a mix of female glue and stored male sperm during egg laying. At room temperature, the eggs incubate for about ten days, more quickly if it is warmer. Larvae feed for four to five weeks, attaining lengths of approximately 3.5 inches/9.2cm before descending the host plant to excavate subterranean chambers in soft earth. Here in Canada and in the northern United States, P. modesta seem to have a single brood each year. I am not sure, but it appears from sighting data that P. occidentalis, at least those from the southwestern US, appear to have at least two broods each year. Adults of this species do not feed, but rely on fats stored from caterpillar days to sustain an adult lifespan of probably only 6-10 days, just long enough for mating and egg laying.

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