ABOUT BOM SPECIES LIST BUTTERFLY HISTORY PIONEER LEPIDOPTERISTS METHODS
The Butterflies of Massachusetts
75 Dreamy Duskywing Erynnis icelus (Scudder & Burgess, 1870)
Dreamy Duskywings and Sleepy Duskywings are actually very sprightly butterflies. Their whimsical names refer to their “closed eyes” --- the lack of a stack of white subapical dots at the “wrist” or leading edge of the dorsal front wing, marks which are usually found on the four other Erynnis species in Massachusetts, Juvenal’s Duskywing, Horace’s Duskywing, Persius Duskywing, and Wild Indigo Duskywing.
Dreamy Duskywing has a more northerly range than Sleepy Duskywing, and is found throughout Canada (Layberry 1998). The ranges of the two overlap across a large area, including Massachusetts. Their May flight periods overlap here as well, although Dreamy’s extends further into June; in addition, they look similar and can be hard to separate in the field. But Sleepy is larger, and more restricted to dry sandy pine-oak habitats, while Dreamy is a habitat generalist. Within Massachusetts, Dreamy is the more widespread and abundant of the two.
Photo: Little Mt. Tom, Holyoke, F Model, May 15, 2009
Scudder and Burgess were the first to describe Dreamy Duskywing as a species in 1870, in a paper given at the Boston Society of Natural History. “Open roads through woods in hilly regions, especially if these be damp from the vicinity of streams, will be found the favorite place of resort for this butterfly, which never swarms, but is often found singly in great numbers” wrote Scudder in 1889, adding that the species was widespread and had been found in “almost every place where there are resident collectors.” For Massachusetts he cites Andover, Amherst, Springfield, Middleboro, Nantucket, and several places near Boston, such as Winchester, Belmont, Wyoming and Mattapan (1889: 1511). Among those “places near Boston” should also be counted Wollaston (now Quincy) where F. H. Sprague found icelus on the 25 of May and the 6 of June 1878 (Sprague 1879).
As Newton naturalist Charles Maynard (1886) put it in that over-used phrase, Dreamy Duskywing was certainly “not uncommon” at the beginning of the 20th century. Scudder’s account of this species, unlike those for the “persius group” of duskywings, seems generally accurate. Though widely collected, there is no way to estimate whether this species has experienced any decline or increase since 1900.
In the mid-20th century, Dreamy Duskywing was listed as “found everywhere” (Farquhar 1934), and was present on both Martha’s Vineyard and Nantucket (Jones and Kimball 1943; Vineyard specimens are in Yale Peabody Museum). In the 1960’s Dreamy Duskywing was collected in Acton and Concord (Walden Pond Reserve) by C. G. Oliver, and in the 1970’s it was found in Medfield, Dover, Needham , and Canton (Fowl Meadows) by R.E. Grey and W. D. Winter (specimens in Yale Peabody Museum and Harvard MCZ).
Host Plants and Habitat
Unlike Sleepy, Juvenal’s and Horace’s Duskywings, which use oaks as host plants, Dreamy Duskywing has been known since Scudder and W. H. Edwards to use mainly poplars and willow. Birch is also widely reported. Many species of poplar, willow and birch can serve as hosts, as well as one legume, black locust (Scott 1986). Some writers (e.g. Iftner et al. 1992; Cech and Tudor 2005) suspect that Dreamy Duskywing may also utilize oaks, but thus far evidence seems to be lacking.
During the 1995-99 Connecticut Atlas eggs or caterpillars of Dreamy Duskywing were found in the wild on Black Willow (Salix nigra) and Quaking Aspen (Populus tremuloides). A surprise was finding Dreamy Duskywing larvae on Black Locust (Robinia pseudoacacia) in some xeric habitats, and Atlas authors wondered whether these might represent a host-specific race or subspecies (O’Donnell et al. 2007). Black Locust is native to continental United States, but was introduced into New England. Dreamy Duskywing is not known to have adopted any non-native host plants.
In Massachusetts, Dreamy Duskywing larvae have been found on both poplar and willow, for example on the Northern Worcester County NABA Count in 2000 and the Lower Pioneer (Springfield area; R. Pease) NABA Count in 1991 and 1992. Caterpillar photographer Sam Jaffe found two Dreamy Duskywing larvae in 2009, one early instar in July in a dry field in Millis on knee-high aspen, and one along powerline cut at Broad Meadow Brook WS in Worcester on a six foot bigtooth poplar in mid-late August, a final instar prior to over-wintering.
Dreamy Duskywing is known as an adaptable species, at home in a variety of open habitats near woods, including both moist areas and dry pine-oak barrens. While Sleepy Duskywing seems to be largely confined to such dry pine-oak barrens, where its host plant scrub oak is found, Dreamy is found in many habitats, from moist with willow to dry with poplars, so that the two duskywings cannot be neatly separated by habitat.
The duskywings are a difficult group to identify to species in the field, and sight reports by less-trained observers probably contain some error. Most MBC members have been through a learning curve with these species. If full identification was not possible, the sighting was reported as ‘duskywing spp.’ in MBC records. These reports are not used in this account.
Relative Abundance Today
MBC records 2000-2007 rank both Dreamy Duskywing and Sleepy Duskywing as “Uncommon” relative to other butterfly species, with the Dreamy somewhat more frequently found than the Sleepy (Table 5). Dreamy is the third most frequently-found duskywing, after Juvenal’s (U-C) and Wild Indigo (U-C). Sleepy and Horace’s are on the low end of Uncommon.
Similarly, the 1986-90 MAS Atlas had found the Dreamy to be “uncommon to common” and the Sleepy to be “uncommon to locally common.”
MBC 1992-2009 records of sightings per total trip reports indicate some decline in this species (Chart 75). The decline is clear only since 2003. The year 1992 is not comparable due to multiple double-digit single-trip counts (outliers), and may be discounted in interpreting the chart.
Chart 75: MBC Sightings per Total Trip Reports, 1992-2009
Linear regression of these data also indicates significant decline 1992-2009, and unadjusted numbers seen show decline 2004 – 2009. By contrast, sightings of Sleepy Duskywing show an increase over this period.
A separate list-length analysis by G. Breed, S. Stichter and E. Crone (2012) showed a statistically significant 53% decline 1992-2010 for Dreamy Duskywing, compared to a statistically significant 104% increase for Sleepy Duskywing.
Statistics published in the Massachusetts Butterflies Season Summary also detail decline in this species. In 2007, 2008, and 2009, the average number of Dreamy Duskywings per trip report decreased 70.5% in 2007, 68% in 2008, 27% in 2009, and 27% in 2010 relative to the average for the preceding years back to 1994. The number of reports of this species, and the maximum number reported, were also down in 2007, 2008, 2009, and 2010 relative to the average for prior years (Nielsen, 2008-2011).
State Distribution and Locations
In MBC records 1991-2010, Dreamy Duskywing was reported from 94 towns, compared to 42 for Sleepy Duskywing. No map is available for this species.
The 1986-90 MAS Atlas found the Dreamy well-distributed across the state, although not as frequent on the southeastern plain, Cape Cod and the islands, or in Hampden County. Today we still have very few records from the southern part of the Connecticut River valley south of Northampton ---only a few from Holyoke, Hampden, Westfield, and Monson. However, there are many records from Berkshire County, especially at higher elevations (see below).
The twenty-year MBC 1992-2011 database has no reports of Dreamy Duskywing from Cape Cod, despite many reports of Sleepy, Juvenal’s and Horace’s duskywings. However, Mello and Hansen (2004) list several reportedly reliable locations for Dreamy on the Cape, and Hansen reports that it can be found at Crane WMA in Falmouth, along with Sleepy Duskywing (Stichter 2005: 32) Neither Dreamy nor Sleepy Duskywing adults are reported on the NABA Counts in July, because their flight period has ended.
On Martha’s Vineyard, Jones and Kimball (1943) had reported Dreamy Duskywing as “not rare” and three of Jones’ specimens (no year, but species determined by J. M. Burns) are at Yale Peabody Museum. The 1986-90 MAS Atlas had no reports from the Vineyard, and in MBC records Dreamy is reported only infrequently and in small numbers. Matt Pelikan reports that at Manuel Correllus State Forest and on the Vineyard generally Dreamy is rare or uncommon, whereas Sleepy Duskywing is common (Pelikan 2002; Stichter 2005: 43).
On Nantucket, whereas Scudder had called Dreamy Duskywing “tolerably common” on that island, by the 1940’s Kimball had only two records, May 25, 1937, and June 1, 1940 (Jones and Kimball 1943). The Atlas had a single (apparently sight) report from Nantucket (Siasconset, 6/8/1988, W. Maple). MBC has no reports from Nantucket, but local observers feel that Dreamy Duskywing is likely to be present (LoPresti 2011).
Locations from which especially high numbers of Dreamy Duskywings have been reported are
Adams Greylock Glen max. 11 on 6/5/2001 P. Weatherbee; Mount Greylock max 13 on 6/5/2005 T. Gagnon et al.; Foxboro Lamson Road max 6 on 5/20/2006 T. Murray and E. Nielsen; Grafton Dauphinase Park max 15 on 5/29/2004 D. Price and W. Miller; Harvard Oxbow NWR max 6 on 5/7/2000 M. Lynch and S. Carroll; Lenox George L. Darey WMA max. 3 on 5/30/2008 F. Model and E. Nielsen; Medford Middlesex Fells max 5 on 5/2/2010 M. Arey; Newbury Martin Burns WMA max 14 on 5/31/2003 S. Stichter et al.; Petersham North Common Meadow TTOR max 6 on 5/25/2009 T. Gagnon et al.; Plymouth Myles Standish SF max 8 on 5/2/2001 D. Peacock; Sherborn power line max 9 on 5/10/2010 B. Bowker; Stow Delaney WMA max 10 on 5/21/2011 M Arey, and 8 on 5/26/2001 B. Walker and E. Barry; Upton Chestnut St. gas line max 16 on 6/4/2000 T. and C. Dodd; Woburn Horn Pond Mountain max. 10 on 5/31/2004 M. Rines; and Worcester Broad Meadow Brook WS max 18 on 5/16/2000 G. Howe.
Other significant locations are
Westfield Barnes Airport 3 on 5/24/2011 T Gagnon; Hoyoke Dinosaur Footprints TTOR 3 on 5/14/2010 T. Gagnon et al; Mt Tom (see photo above); Cummington; Northampton Florence max 5 on 5/13/2004 T. Gagnon; Belchertown Quabbin Park; Petersham North Common Meadow TTOR 4 on 5/29/2006 B. Benner et al.; Acton/Concord Fort Pond Brook; Northborough; Royalston Tully Lake; and Hubbardston Barre Falls Dam.
Broods and Flight Period
Dreamy Duskywing is univoltine throughout its range, except in the southern Appalachians (Opler and Krizek 1984; L. Harris 1972 reports a partial second brood in north Georgia.). According to MBC records, the single flight period here extends from mid-April to early July at the extremes, through the most numbers are seen in the last two weeks of May and the first two weeks of June (http://www.naba.org/chapters/nabambc/flight-dates-chart.asp).
In 20 years of MBC records, from 1991 through 2010, there have been four years in which the first sighting of a Dreamy Duskywing was in April, rather than May: 4/16/2000 Westfield, T. Gagnon; 4/27/1991 “Massachusetts” T. Dodd; 4/30/2004 New Salem D. Small/R. Cloutier/S. Cloutier; and 4/30/2010 Sherborn power line B. Bowker.
Seven of the twenty first sighting dates were in the first week in May, 5/1 – 5/7, and the remaining nine first sighting dates were the second or third week in May.
Around 1900 Scudder reported that the earliest known dates for Dreamy Duskywing’s appearance in New England were May 10 near Boston, and May 11, Nantucket (1899: 1513). This was a well-known and widely collected species, so some reliance may be placed on these dates. MBC data suggest that Dreamy Duskywing’s first appearance may be occurring earlier now than a century ago.
In the 20 year period under review, the last sightings of Dreamy Duskywing occur with remarkable frequency (9 out of 20 years) in the last week of June. They are therefore hardly ever reported on the July NABA Counts. In three of 20 years, the last sighting stretched into July: 7/7/2008 Cummington, B. Spencer; 7/5/2009 Newbury Martin Burns WMA S. Stichter; and 7/1/ 2003 Cape Ann D. Savich and C. Tibbits.
A century ago Scudder wrote that Dreamy Duskywing was found “throughout June, and occasionally, about the latitude of Boston, until the end of the first week of July” (1889: 1513). The late flight dates in MBC records are remarkably similar.
Kimball (Jones and Kimball 1943) reported for Martha’s Vineyard that Dreamy Duskywing was “double-brooded” but this is probably an error (as pointed out by Leahy in the MAS Atlas), perhaps resulting from confusion with some other duskywing species. Wild Indigo and Horace’s are the only duskywings known to be double-brooded in Massachusetts.
It is not outside the realm of possibility that this species might decline in Massachusetts with climate warming, given its northerly range and lack of a lowland seaboard range in southern states (Table 6). A northward and higher-elevation range contraction might first be noticed in declining sightings from Cape Cod and the islands—which may already be evident (see above).
Neither habitat loss nor host plant specialization are the major limiting factors in Dreamy Duskywing’s distribution. In Connecticut, the 1995-99 Atlas found no apparent change in this species’ distribution between pre-project and project periods, finding it still Common in that state (O’Donnell et al. 2007).
© Sharon Stichter 2012
page updated 12-3-2012
ABOUT BOM SPECIES LIST BUTTERFLY HISTORY PIONEER LEPIDOPTERISTS METHODS