Other Common Names
There are 2 Groups within this species complex and each seems to be quite specific in host plant preferences & range:
Nominate form is known as the "Columbia Silk Moth" or "Larch Silkworm (larva)"
The 2nd is better known as ssp. gloveri or "Glover's Silk Moth"
Synonyms and other taxonomic changes
Glover's Silkmoth (H. c. gloveri) was formerly considered a separate species ... and still is by many!
Taxonomic work continues and there is mounting evidence to support the former taxonomic level of recognition as a distinct species from H. columbia.
Size
wingspan 80-100 mm
larvae to 90 mm long, and 20 mm wide
Identification
Adult: easily confused with
Cecropia Moth [and
vice versa]; wings dark reddish-brown from base to PM line, dark gray in subterminal area, and pale yellowish in terminal area; AM and PM lines thick, white; pale yellow or whitish discal spots on all wings (spots are oval on forewings, crescent-shaped on hindwings); large black spot near apex of forewing; no red shading beyond PM line on forewing and hindwing [this last characteristic distinguishes
columbia from
cecropia]
Larva: body green with prominent, paired dorsal tubercles and smaller lateral ones; head green with bluish labrum and short dark line at sides of frons; four small black spots in bluish anterior half of prothoracic shield; spined, reddish and black tubercles on T2, T3, and A1; white dorsal tubercles on A2 to A7 tinged with yellow near tip; large, white middorsal tubercle on A8 with black spots, and with yellow tint at tip; white supraspiracular and subspiracular tubercles with blue base; white spiracles; prolegs larger on A10 than on other segments
[description adapted from forestpests.org]
Range
British Columbia to Nova Scotia and adjacent northern United States; in the west, occurs south to Texas and central Mexico (see
US distribution map)
Columbia Silk Moth (most often associated with Tamarack bogs):
Canada: eastern Maritime Prov's., Great Lakes region extending slightly west into the eastern edge of the Plains.
USA: New England, upstate New York and "upper" Great Lakes States (Michigan & Wisconsin)
Glover's Silk Moth (associated with various habitats from moist forests to deserts):
Canada: Central Canada Plains
USA: Rocky mountain States, western Plains, Great Basin, eastern slopes of the Sierra Nevadas and Mountains of the Sonoran Desert region
Mexico: Mountainous areas of the northern & central Mexican states
Range overlap and interactions between columbia nominate and ssp. gloveri appear to be quite limited raising questions regarding the relationship between the two taxa.
Habitat
Columbia group
forests with poorly drained, boggy, acidic soil; Tamarack forests; suburban gardens; wide variety of wooded habitats
Gloveri group
Mountains, Plains & Deserts nr. seasonal water sources; suburban gardens; wide variety of wooded habitats
Season
adults fly from May to July
larvae from July to September
H. gloveri has adult flight periods from March thru August (may be partially bivoltine in arid & southern parts of the range)
Food
In eastern North America [ssp. columbia], the preferred food of larvae is Tamarack (American Larch - Larix laricina); in the west [ssp. gloveri], larvae eat leaves of Alder (Alnus sp.), Birch (Betula sp.), Antelope Bitterbrush (Purshia tridentata), Buckbrush (Ceanothus sp.), Buffaloberry (Shepherdia sp.), Plum & Cherry (Prunus sp.), Rose (Rosa sp.), Russian Olive (Eleagnus angustifolius), Willow (Salix sp.), etc.
Life Cycle
one generation per year; eggs are laid singly on food plant, and hatch in 8-19 days, depending on temperature; overwinters as a pupa in spindle-shaped cocoon attached lengthwise to twig or trunk of tree or shrub
Remarks
The H. columbia group includes the following:
ne. USA, Great Lakes region of US & Canada, & much of e. Canada
USA & Canada / Rocky Mountains, Western Plains, and Great Basin e. of the Sierras
NO IMAGE AVAILABLE
Plains of Central Canada
Synonymized with gloveri
Form "nokomis" is often described as being a diminutive & slightly divergent population from the nominate gloveri. Many specimens identified as nokomis often appear to possess characteristics suggestive of cecropia influence, particularly red scaling along the postmedial bands ...... possible blend zone???. Additionally, the range and locality data for many specimens identified as "nokomis" originate from areas of likely contact between the potential parent taxa - "cecropia x gloveri"
NOTE: The specimen pictured in the link below is strikingly similar to many "cecropia x gloveri" hybrids and blends
NO IMAGE AVAILABLE
Rocky Mountains of the USA & Canada (High Elevations)
Synonymized with gloveri. Described as being a high altitude diminutive form. Specimens identified as reducta have been reported along the Rockies and are likely the result of environmentally induced traits. The small size and compact appearance does not seem to be genetic. Stocks collected at higher elevations and reared at lower ones seem to produce "normal sized and patterned adults".
sw. USA - incl. se. Arizona & sw. New Mexico - south into central Mexico
Hyalophora pop's from the mountains of central Mexico north into the Sonoran region of n. Mexico & se. Arizona (sw. New Mexico) "appear to be" geographically & temporally restricted from most other Hyalophora. These populations deviate from other columbia/gloveri as follows:
1) Peak time of year for adult activity
(Often bivoltine with an active late July-August emergence and a smaller spring emergence between April-early June)
2) Slightly larger size
(often approaching that of cecropia)
3) Degree of coloration & pattern (refer to the images below for details)
NOTE:
a) Extensive reddish-burgandy coloration extending "submarginally" as seen in euryalus (instead of the softer gray coloration typical of most other "gloveri" populations). There has been some thought, this increase in reddish coloration may be environmentally induced. There is a tendency in several of the Hyalophora species to exhibit more red when exposed to warmer temperatures (less dramatic temp differentials between day and night = "more reds").
b) They exhibit tremendous variability in the shape and size of the discal crescents, ranging from long euryalus-like to short columbia/gloveri-like to absent in some examples.
c) The presence of a discernable red postmedial band - best viewed ventrally (as seen in cecropia)
NOTE: Specimens from central Mexico are often more striking and divergent in appearance.
These members of the "columbia species group" often spark debate among specialists and hobbyists alike. "Are they possibly hybrids, a distinct subspecies or something else" ???
Internet References
live images of all life stages plus common name reference [Columbia Moth], distribution, description, food plants, biology, and other info (Bill Oehlke, Prince Edward Island)
live adult and larva images plus common name reference [Columbia Silkmoth] (Moth Photographers Group)
live adult image of subspecies [i]H. c. gloveri by Phynix Carlson, plus US distribution map, description, distribution, food plants, biology, references (butterfliesandmoths.org)
pinned adult images - 1 specimen of subspecies
H. c. gloveri, and 2 specimens of nominate subspecies (CBIF)
food plants plus adult description and photo of forewing (Nicky Davis, Utah)
pinned adult image plus food plants, biology, description, and other info (Manitoba's Silk Moths, naturenorth.com)
live larva image plus description, biology, distribution, and common name reference [Larch Silkworm; larva] (C.T. Maier et al, USDA Forest Service, forestpests.org)
foodplants plus distribution, links to images, references (Markku Savela, FUNET)
distribution in Canada list of provinces (CBIF)
