The discovery of a population of Antrodiaetus unicolor (Hentz) in Michigan is reported, resulting in the first state record for the mygalomorph family Antrodiaetidae. New county records for another mygalomorph spider, Sphodros niger (Hentz) (Atypidae), including one which represents a significant Michigan range extension, are presented and the occurrence of the genus in Michigan is clarified

Swanson, Daniel R

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The Great Lakes Entomologist 
Volume 43 
Numbers 1 - 4 - 2010 Numbers 1 - 4 - 2010 Article 9 
April 2010 
On the Mygalomorphae (Araneae) of Michigan 
Daniel R. Swanson 
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94 THE GREAT LAKES ENTOMOLOGIST Vol. 43, Nos. 1 - 4
11001 Maiden Lane Apt. 1, Ann Arbor, MI 48105.  (e-mail: drswanny@gmail.com).
On the Mygalomorphae (Araneae) of Michigan
Daniel R. Swanson1
Abstract
The discovery of a population of Antrodiaetus unicolor (Hentz) in Michigan 
is reported, resulting in the first state record for the mygalomorph family Antro-
diaetidae.  New county records for another mygalomorph spider, Sphodros niger 
(Hentz) (Atypidae), including one which represents a significant Michigan range 
extension, are presented and the occurrence of the genus in Michigan is clarified.
 
____________________
The Mygalomorphae are often large, conspicuous spiders comprising 
the taxon sister to the much larger clade of true spiders, the Araneomorphae. 
Members of the group possess parallel fangs and two pairs of book lungs, in 
contrast to the diaxial chelicerae and single pair or absence of book lungs found 
in most araneomorph spiders.  The infraorder encompasses 15 families with 
the greatest diversity found, as is the usual case, in the tropics.  Eight of these 
families are known to occur in the United States and basic information on 
identification, natural history and taxonomy for each of these families may be 
in found in Ubick et al. (2005).  Of the Mygalomorphae, only two atypids have 
previously been reported in Michigan (one erroneously).  Herein, a new myga-
lomorph family is added to the list of spiders occurring in Michigan with the 
discovery of a population of Antrodiaetus unicolor (Hentz, 1842) in Ann Arbor. 
Additional records are presented for the black purseweb spider Sphodros niger 
(Hentz, 1842) and the presence of the red-legged purseweb spider Sphodros 
rufipes (Latreille, 1829) is discussed.
Antrodiaetidae.  The trapdoor spiders in the family Antrodiaetidae are 
arranged into 2 genera and 32 species worldwide (Platnick 2009).  Both genera 
are restricted to but widely distributed across the United States and portions of 
southwestern Canada with the exception of two species of Antrodiaetus found 
in Japan (Coyle 2005).  The family was revised and information on natural 
history was presented in a series of studies by Coyle (1968, 1971, 1975) and 
additional natural history information was given by Coyle and Icenogle (1994). 
Atypoides was later synonymized with Antrodiaetus based on molecular studies 
(Hendrixson and Bond 2007).  Species of Aliatypus are found in the southwestern 
United States (Coyle 2005).  Antrodiaetus is widespread across the United States 
though previous records report A. unicolor from only as far north as southern 
Illinois, Indiana and Ohio and A. robustus (Simon, 1891) from Pennsylvania 
and eastern Ohio (Coyle 1971, Sierwald et al. 2005).
The trapdoor spiders in the genus Antrodiaetus are commonly known as 
folding-door or collar-door spiders.  The name seems fitting as the silken folds 
or “curtains” that line each side of the burrow mouth render spiders of this 
genus instantly recognizable.  These distinctive trapdoor spider burrows as 
well as their occupants were observed on the night of 21 May 2009 in Nichols 
Arboretum located in the northeastern portion of the University of Michigan 
Central campus in Ann Arbor.  One adult female was taken.  Upon returning 
on several later dates, the burrows were counted, spiders and burrows were 
photographed (Figs. 1-3) and more specimens were collected.
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Swanson: On the Mygalomorphae (Araneae) of Michigan
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2010 THE GREAT LAKES ENTOMOLOGIST 95
Figure 1. Antrodiaetus unicolor, adult female, at burrow entrance.
The site of collection is a mesic oak-maple forest, typical of lower Michigan, 
in a glacial outwash.  The soil consists of Miami loam, 25-30% slope as character-
ized by Engel (1977).  Invasive species including buckthorn and honeysuckle are 
common and hints of extirpation efforts are noticed occasionally.  The particular 
portion of the Arboretum in which the spiders reside comprises the periphery 
along the lower northern Arboretum road from the Washington Heights entrance 
(Intersection 1) to the trail junctions east of the Oak Openings (Intersection 2) 
and the trail leading from this road to the beginning of the wooden staircase 
near the River Landing on the Huron River (Intersection 7).  The distances from 
Intersection 1 to Intersection 2 (hereafter Lower Road) and from Intersection 
2 to Intersection 7 (hereafter Ridge Trail) are 0.24 and 0.32 km, respectively. 
Place names and distances are taken from the trail maps posted throughout 
the Arboretum.  The periphery of the Lower Road was densely covered in leaf 
litter nearly in its entirety; very little bare soil was visible.  The Ridge Trail 
periphery, on the other hand, had much less leaf litter and closer to 50% of the 
soil was bare.  Areas beyond the periphery of the trail were not searched as 
the spiders were common enough around the trail.  Additional investigation 
was further deterred since the sloping hillsides were posted as protected areas.
On one evening in late May of 2009, 237 burrows were counted from the 
Arboretum entrance to the wooden staircase.  In most cases, the spider occupants 
could be seen at the entrance of the burrow but this was not required for count 
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96 THE GREAT LAKES ENTOMOLOGIST Vol. 43, Nos. 1 - 4
Figure 2. Same burrow as Fig. 1, entrance concealed.
Figure 3. Antrodiaetus unicolor, adult female, grappling with “lure”.
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Swanson: On the Mygalomorphae (Araneae) of Michigan
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2010 THE GREAT LAKES ENTOMOLOGIST 97
inclusion.  Of these burrows, 43 burrows were counted along the Lower Road 
while 194 burrows were counted along the Ridge Trail.  The sheer number of 
individuals seems to indicate that this population has been living in the Arbo-
retum for some time and has simply remained unnoticed.   Burrow diameter 
ranged from about 5-18 mm.  In each situation, more burrows were counted on 
the higher side of the path and burrows were situated so the spider was facing 
downhill.  Burrows were commonly found under the large surfaced tree roots 
or under the occasional log set out to line the path on the Ridge Trail.  In a few 
instances, burrows were found on the lateral portion of the pathway itself.  Some 
burrows were carved through fallen leaf litter but it was more common to see 
them in bare soil.  The difference in leaf litter coverage mentioned previously 
may account for the discrepancy in burrow density between the Lower Road 
and the Ridge Trail.
It was fairly easily to induce a quick pounce from the burrow using a small 
twig or blade of grass but the spiders seemed fairly cautious as well as incred-
ibly fast.  It is likely that the presence of numerous flashlights made them more 
wary.  Discovery of a superior lure afforded a better chance to study the spiders. 
A stem with a large bud or unopened flower was particularly attractive as an 
imitation food source; in many cases, individuals would come completely out of 
the burrow in pursuit of it.  Presumably, the fleshy, somewhat moist feeling of 
the plant bud better simulated a living organism than a stick or grass blade. 
Despite this trickery, one large female, when continuously presented with the 
same bud, grappled with it for a full 2.5 minutes.
Specimens were identified using the key to females constructed by 
Coyle (1971).  The spider’s identity could easily be limited to A. robustus or A. 
unicolor.  The length: width ratio of the sternum fit within the range described 
for A. unicolor.  Additionally, the short thickened black setae characteristic of 
A. unicolor was observed immediately posterior to the pedicel, contrasting the 
long, thin setae expected for A. robustus.  The author also found no anterior 
lateral spinneret vestiges, this absence being another feature attributable to A. 
unicolor.  As a result, the specimens were identified as A. unicolor.  Photographs 
of some of these characters were sent to Dr. Brent Hendrixson for confirmation; 
he agreed with the author’s determination.  However, two notes regarding the 
taxonomic status of this species should be considered.  First, Coyle (1971) notes 
A. robustus may be nothing more than a northern genetic variant of A. unicolor. 
Second, Hendrixson and Bond (2005) suggest and Coyle (2005) agrees that A. 
unicolor is probably made up of a complex of species.
As a direct result of this discovery, two large adult females (20-22 mm.) 
were vouchered in the University of Michigan Museum of Zoology (UMMZ) bear-
ing the following locality information: MICHIGAN, Washtenaw Co., Ann Arbor, 
Nichols Arboretum, Ridge Trail from Oak Openings to Huron River, 30 May 
2009, 42.2823 -83.7220, DRS#2009-052, 240 m., D. R. Swanson, Antrodiaetus 
unicolor (Hentz), det. D. R. Swanson 2009, NEW STATE RECORD - Michigan. 
Several adult females, including the first specimen obtained from the locality 
on May 21, reside in the author’s personal collection (DRS).  Aside from the 
date on the first female, these specimens have locality information identical to 
the museum vouchers.
The new record reported above constitutes a northward extension of the 
species current range as set out by Coyle (1971).  The new locality is approxi-
mately 330 air km north-northwest of the Hocking Hills State Park area in 
Hocking County, Ohio; this is listed in the reference as Ash Cave State Park 
and Cantwell Cliffs State Park.  It is also approximately 370 and 380 air km 
northwest of Pittsburgh and Penn Hills, Allegheny County, Pennsylvania, re-
spectively, an area in which both A. unicolor and A. robustus are found.  It is 
also worth noting here the nearest locality for A. robustus: approximately 255 
air km to the southeast in Canton, Stark County, Ohio.
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Atypidae.  The Atypidae, whose members are commonly known as 
purseweb spiders, contains 3 genera and 43 species worldwide (Platnick 2009). 
In the Nearctic region, the 7 species belonging in the genus Sphodros Walckenaer 
and the single species belonging in Atypus Latreille are restricted to the eastern 
half of the continent (Coyle, 2005a).  The family was revised by Gertsch and 
Platnick (1980) while some aspects of natural history were reported by Coyle 
and Shear (1981), Beatty (1986) and Edwards and Edwards (1990).
Previously, the black purseweb spider, Sphodros niger (Hentz 1842), has 
been taken in Ingham and Clinton County, Michigan (Gertsch and Platnick, 
1980).  Both were single males caught in pitfall traps.  This species was later 
reported as having been collected in the Edwin S. George Reserve in Livingston 
County (Cameron, 1993; pers. comm.).  Additionally, the author has seen images 
that clearly represent S. niger reportedly photographed in Ada, Kent County, 
Michigan (http://bugguide.net/node/view/220129/bgimage).
The only specimen of Atypidae, a single male S. niger, already residing in 
the UMMZ bears the following label: MICHIGAN, Lenawee Co., Adrian Coll. 
Arb. @ SE Round Lk., 3 June 1992, field, R. W. Husband, det. M. O’Brien ’93 
(1♂).  The recent sorting of old pitfall material stored in the UMMZ has yielded 
additional records for the species, including one that represents a significant 
northward range expansion in Michigan.  Two males bear the locality informa-
tion: MICHIGAN, Washtenaw Co., Matthaei Botanical Garden nr. Dix Pond, 
small pitfall, 15-19 June 1996, G. Hammond, det. D. R. Swanson 2009 (2♂). 
Two more males bear the following locality information: MICHIGAN, Crawford 
Co., T25N-R4W-Sec. 32, 23-30 June 1997, Stand 8, Plot 3, C. Sculley, pitfalls, 
det. D. R. Swanson 2009 (2♂).  One of these males is missing the abdomen but 
the form of the chelicerae and endites, in addition to the similarity to the other 
complete specimen, make identification indisputable.  Additionally, Prof. H. D. 
Cameron has kindly donated another specimen to the UMMZ.  It represents 
the only female in the Michigan collections and bears the following locality in-
formation: MICHIGAN, Washtenaw Co., Pittsfield, Twp., S. of US12 on Moon 
Rd., Sec. 32, 33, digging in thick woods, 13 April 1998, Ryan F. Neice, det. H. 
D. Cameron 1998 (1♀).  All of the above specimens are now deposited in the 
UMMZ collection.
A confusing and overlooked point in the literature is the presence of 
another atypid, the red-legged purseweb spider S. rufipes in Michigan.  The 
binomial Sphodros milberti Walckenaer, 1837 was officially synonymized under 
this species by Gertsch and Platnick (1980).  S. rufipes is known from Maryland, 
New York and Rhode Island to southern Illinois and eastern Kansas (Gertsch 
and Platnick 1980, Morrow 1986) and Snider (1991) reported Atypus milberti 
(Walckenaer) as occurring in Berrien, Clinton, Ingham and Jackson counties in 
Michigan.  Snider also noted the latter three counties as having vouchered speci-
mens in the Michigan State University Arthropod Research Collection (MSU). 
Sierwald et al. (2005) then based inclusion of Sphodros rufipes (Latreille) in 
their list for Michigan on Snider’s records.  The author has seen the specimens 
residing in MSU: five males from four different collecting events in Ingham 
County, one male from a single collecting event in Clinton County and one male 
from a single collecting event in Lake County.  As the latter may constitute an 
unreported record, the locality data is provided here: MICHIGAN, Lake Co., 
Big Star Lake, 6-June-1973, W. Walker, ex. leaf litter (1♂).  One of the males 
from Ingham County could be the one mentioned in Gertsch and Platnick (1980) 
but the Clinton County record represents another individual.  The Berrien and 
Jackson County specimens of Snider (1991) remain unknown to the author.
All of the MSU specimens clearly represent S. niger.  The piceous color of 
the legs and the palpal morphology leave no question regarding the identity of 
the spiders.  The confusion was a result of the specimens being misidentified 
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Swanson: On the Mygalomorphae (Araneae) of Michigan
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2010 THE GREAT LAKES ENTOMOLOGIST 99
as A. milberti, an understandable error as this particular misidentification was 
not at all uncommon in the past (Gertsch and Platnick 1980).  Furthermore, 
Sierwald et al. (2005) designated S. niger as having a “predicted” occurrence 
in Michigan; obviously the set of Michigan records provided by Gertsch and 
Platnick (1980) were overlooked.  Ultimately, S. niger remains the only atypid 
known to occur in Michigan.
Acknowledgements
I thank Mark O’Brien, Insect Division, UMMZ, for his insight and guidance 
in preparing the manuscript, his beautiful photographs which supplement this 
text and his general support in all my entomological endeavors.  I owe thanks to 
Gary Parsons, Arthropod Research Collection, MSU, for the hospitable visits to 
the collection under his care and his helpful correspondence regarding its speci-
mens.  I am also grateful to Prof. H. D. Cameron, University of Michigan, and 
Dr. Brent Hendrixson, Millsaps College, each for their arachnological expertise 
pertaining to the identification of the spider.  I would also be remiss if I did not 
offer thanks to my field assistants, A. Heldt and C. Silliman, for the hours spent 
in the dead of night fishing large spiders out of their burrows.
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On the Mygalomorphae (Araneae) of Michigan

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On the Mygalomorphae (Araneae) of Michigan

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