Distribution and Conservation Status of the
Rusty Gravedigger, Cambarus miltus, a Poorly Known Gulf
Christopher A. Taylor, Guenter A. Schuster, Courtney L. Graydon,
and Paul E. Moler
Southeastern Naturalist, Volume 10, Issue 3 (2011): 547–552
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2011 SOUTHEASTERN NATURALIST 10(3):547–552
Distribution and Conservation Status of the
Rusty Gravedigger, Cambarus miltus, a Poorly Known Gulf
Christopher A. Taylor1,*, Guenter A. Schuster2, Courtney L. Graydon3,
and Paul E. Moler4
Abstract - Cambarus (Lacunicambarus) miltus (Rusty Gravedigger Crayfish) is a primary
burrowing crayfish known from a limited portion of the Gulf Coastal region of the
United States. The lack of form I males in collections has in the past prevented specieslevel
identifications and hampered conservation reviews. We conducted an intensive
status survey for C. miltus during 2007 and 2008. Our results suggest that the species
is much more widespread than previously known and that conservation attention is
unwarranted. Preferred habitat for the species is ephemerally flooded and thinly wooded
floodplains of small streams and swamps.
Cambarus (Lacunicambarus) miltus Fitzpatrick (Rusty Gravedigger Crayfish;
Fig. 1) was described from 10 specimens collected at a single location adjacent
to D’Olive Creek (recorded incorrectly as d’Olide Creek) in Baldwin County, AL
(Fitzpatrick 1978). The type-locality is located along the floodplain of D’Olive
Creek approximately 250 m upstream of Mobile Bay. The species was placed
in the subgenus Lacunicambarus Hobbs due to burrowing behavior and the
morphology of its chela and cephalothorax. Cambarus miltus was distinguished
from other members of the subgenus by a combination of gonopod, epistome,
and annulus ventralis characters. In 1990, Fitzpatrick (1991) did an extensive
survey of 49 sites in the lower 2/3 of Baldwin County to find additional populations.
He discovered that the original colony on which the description was based
no longer existed; however, he found another colony on an island about 50 m
upstream from the original site. He speculated that the original colony moved to
the new location possibly because of a recent storm and inundation of the habitat
by salt water. He also identified two other potential populations (Fish and Perdido
river drainages) of C. miltus; however, because he was not able to collect form I
males, he felt he was unable to verify their identity. Although he speculated that
they probably represented C. miltus, the individuals he collected had features
resembling other species in the subgenus Lacunicambarus that occurred in the
Gulf coastal region of Alabama and Florida. Although it was listed as a candidate
1Prairie Research Institute, Illinois Natural History Survey, 1816 S. Oak, Champaign, IL
61820. 2Department of Biological Sciences, Eastern Kentucky University, 521 Lancaster
Avenue, Richmond, KY 40475. 3Alabama Department of Conservation and Natural Resources,
State Lands Division, 64 North Union Street, Montgomery, AL 36130. 4Florida
Fish and Wildlife Conservation Commission, 1105 SW Williston Road, Gainesville, FL
32601. *Corresponding author - firstname.lastname@example.org.
548 Southeastern Naturalist Vol. 10, No. 3
species, the US Fish and Wildlife Service (Hartfield 1991) declined to propose
listing of C. miltus as threatened or endangered due to the need for additional
surveys to better ascertain the distribution of this species. Taylor et al. (1996)
listed C. miltus as threatened using criteria developed by the American Fisheries
Society. They also reported it not only from Alabama, but also from neighboring
Florida, based on personal communication with Fitzpatrick; however, the disposition
of specimens upon which Fitzpatrick extended the range of C. miltus into
Florida is not known. A more recent assessment (Taylor et al. 2007) continued
to list it as threatened and also listed Florida as part of the range of the species.
In both Taylor et al. (1996) and Taylor et al. (2007), limited known natural range
was the primary criterion used to warrant it’s classification as threatened.
This project was undertaken to address the uncertainty surrounding the historical
data and to assess the distribution and status of C. miltus. Our goals were:
1) collect additional individuals from the populations described in Fitzpatrick
(1991) to ascertain if these populations are in fact C. miltus; 2) do a more extensive
survey of coastal streams and associated habitats in southern Alabama and
western Florida; 3) record habitat parameters at sites containing C. miltus.
Beginning with the type locality, we visited all locations previous visited by
Fitzpatrick during his 1990 survey from which he reported possible C. miltus
Figure 1. A) Female Cambarus miltus specimen from Corn Creek, Baldwin County, AL,
photo © G.A. Schuster; B) Form II male C. miltus specimen from Yellow River, Okaloosa
County, FL, photo © C.A. Taylor.
2011 C.A. Taylor, G.A. Schuster, C.L. Graydon, and P.E. Moler 549
specimens. After an assessment of the habitat at these locations, additional
sites with similar habitats were examined for the presence of C. miltus. These
additional sites were selected by locating streams, marshes, swamps, and
other promising aquatic habitats on topographic maps, and visiting the sites
to determine the presence of burrows in the riparian areas adjacent to standing
water bodies. If burrows were present, we progressed to digging and opening
the burrows in order to determine which crayfish species inhabited them.
Fresh burrows (i.e., burrows with chimneys of wet mud, indicating recent burrowing
activity) were excavated by hand or using a shovel and garden trowel.
Usually, the burrow was excavated to the level of the ground water, and then
the water was agitated in order to entice the crayfish to come to the surface.
This method was often successful in capturing the crayfish; however, when
crayfishes did not come to the surface, the burrow was more thoroughly excavated
in an attempt of capture it. Often, burrows that appeared to be active
were not occupied or the crayfish could not be collected due to underground
obstructions, such as roots, that prevented further excavation. In these cases,
alternate burrows were excavated. For sites in Florida, one of us (P.E. Moler)
worked by himself and excavated 8–10 burrows per site. The remaining effort
in Alabama usually involved at least three workers (sometimes as many as
six) excavating burrows, and where burrows were abundant, as many as 30 or
more burrows were excavated. These efforts were used to determine presence
or absence of C. miltus at a location, and not to determine population densities.
At several sites, a seine was also used to determine if C. miltus might be in the
surface water. If C. miltus specimens were not captured after one to two hours
of excavating burrows and seining (if employed), the site was classified as not
containing the species and abandoned. Voucher specimens were preserved in
70% ethanol and returned for deposition in the Crustacean Collection of the Illinois
Natural History Survey (INHS).
In addition to the field work, type specimens housed at the United States
National Museum of Natural History Smithsonian Institution (USNM) were examined
for comparison with specimens collected in the field. Attempts were also
made to locate the specimens reported by Fitzpatrick (1991) by searching the
holdings of the USNM, University of Alabama Decapoda Collection (UADC),
and the Tulane University Crustacean Collection (TU).
In this study, a total of 110 sites were visited across extreme southern Alabama
and northwestern Florida (Fig. 2; see Supplemental Appendix 1, available online
at https://www.eaglehill.us/SENAonline/suppl-files/s10-3-928-Taylor-s1, and, for
BioOne subscribers, at http://dx.doi.org/10.1656/S928.s1). Sites occurred from the
Escatawpa drainage in southwestern Alabama to the Apalachicola drainage in
northwestern Florida. Of the sites visited, 28 were found to have C. miltus present
(Fig. 2) including those locations in the Fish and Perdido river drainages listed by
Fitzpatrick (1991) as possible C. miltus populations. All specimens were collected
from burrows. Depending on proximity to other known locations, voucher specimens
from most sites were preserved and deposited into the Crustacean Collection
550 Southeastern Naturalist Vol. 10, No. 3
of the Illinois Natural History Survey (INHS). Previously known records for
C. miltus, including the type locality, represent the western boundary for the species,
whereas specimens collected from the Chipola River (Apalachicola River
drainage) in Calhoun County, FL, extend the known range of the species by approximately
275 km to the east. The number of individuals collected by us at sites
in Alabama ranged from 1 to 10, with an average of 4. An average of 1 individual
was collected from the 8 to 10 burrows excavated at locations in Florida.
Three additional new sites for C. miltus not visited by us are also plotted on
our distribution map (Fig. 2). Specimens collected from Dyas Creek, Baldwin
County, AL in 1972 were found in the Crustacean Collection of the USNM (USNM
207594), and two locations in the Conecuh National Forest in Covington County,
AL were reported by Welch and Eversole (2007). Gender and form of specimens
from these latter two locations are not known as vouchers were not saved.
A suite of qualitative habitat characteristics was commonly encountered where
C. miltus was located. The predominant general habitats that C. miltus apparently
prefers are low-lying, wooded, seasonally flooded floodplains along streams. The
trees typically are widely spaced with some ground cover, but with little or no
dense shrub layer. Cypress, magnolias, and hackberries were often the most common
forms of woody vegetation found in these floodplains. The burrows often
were located close to trees, followed roots, and could be quite difficult to excavate.
Usually the water table was within 30 cm from the surface, and in some cases much
closer. The burrows were usually one-third to one meter deep with a single main
chimney and multiple side branches that came to the surface with either much
smaller chimneys or no chimneys at all. The side branches tended to be horizontal
in general direction, and sometimes the crayfishes were found in the side channels
Figure 2. Distribution map showing the locations of all sites visited during the study.
2011 C.A. Taylor, G.A. Schuster, C.L. Graydon, and P.E. Moler 551
near the surface. The terminus of the burrow was an enlarged chamber littered with
fine to coarse organic debris, and was usually 0.5–1.0 m below the surface. It was
also determined that a suite of habitat characteristics usually identified areas where
C. miltus would not be found. These included: deep-cut streams with high banks,
areas where the water table is greater than 1 m below the surface, riparian zones
covered with a dense shrub layer or sedges, or open areas without trees.
Cambarus miltus was sometimes found in areas that were not considered
typical habitat. Eight of these included areas under highway bridges adjacent to
streams where the water table was close to the surface (often with small pools
of standing water) and the soil was covered with large riprap or dense growths of
vegetation (grasses or sedges). In addition, specimens from Florida were sometimes
collected from burrows dug directly into river banks.
Finally, Fitzpatrick (1978) commented on the overall brick-red coloration in
his description of C. miltus. We found that that character is not consistent across
the range of the species and may be an artifact of soil type at and near the type
locality. Specimens collected in Baldwin County, AL did indeed have an overall
brick-red coloration (Fig.1A), but those specimens found in more easterly locations
in Florida were deep blue in basal color, with only the mid-dorsal stripe
down the abdomen and tips of the chelae being reddish (Fig. 1B).
Cambarus miltus was described (Fitzparick 1978) from specimens collected
only at the type locality. Given this limited known range, C. miltus was considered
for listing under the federal Endangered Species Act (ESA). A resulting
status survey (Fitzpatrick 1991) indicated that the species might be distributed
along other streams in Baldwin County, AL. However, Fitzpatrick (1991) declined
to confirm the presence of C. miltus at those sites due to the lack of form I
males. The uncertainty surrounding the range of C. miltus was again raised when
Taylor et al. (1996) listed the species from Florida without confirmed records.
This uncertainty regarding total range most likely prevented the listing of C. miltus
under the ESA. Our field results confirm that C. miltus occurs across the Gulf
Coastal region from the east side of Mobile Bay east to the Apalachicola River
drainage in northwestern Florida (Fig. 2). Within that range, the species most
frequently occurs in seasonally flooded and thinly wooded floodplains of small
streams with water tables less than 30 cm deep. Other habitats include in or along
stream banks with open, low grasses or exposed mud. Although under-sampled in
this study, the amount of suitable habitat for this species in the Choctawhatchee
and Chattahoochee river drainages in southeastern Alabama and southwestern
Georgia makes it possible that the species also occurs there. Our failure to find
the species on the west side of Mobile Bay, finding instead a closely related but
potentially undescribed species of Cambarus (Lacunicambarus) in the same
habitat type, argues for western Baldwin County, AL as the western terminus of
the range of C. miltus.
Our results greatly increase the known range for C. miltus and document its
presence in several Gulf drainages and across a significant portion of the western
panhandle of Florida. Given the total known range (approximately 19,000 sq. km.)
552 Southeastern Naturalist Vol. 10, No. 3
and abundance of suitable habitat within that range, we believe C. miltus to be
a stable species. Its listing as a species of conservation concern by private (i.e.,
American Fisheries Society) and government (US Fish and Wildlife Service) entities
is unwarranted at this time and was an artifact of a lack of targeted sampling
efforts. Using conservation ranking standards developed by the International
Union for the Conservation of Nature (IUCN), C. miltus would be listed as least
concern due to its range size and lack of evidence for population declines or fluctuations.
The collection of primary burrowing crayfishes is a time-consuming and
labor-intensive endeavor. Given that approximately 22% (39 species) of species
recognized as either endangered or threatened in a recent conservation review
(Taylor et al. 2007) were primary burrowers, we hope that that our results will spur
increased efforts to assess the conservation status of these crayfishes.
We would like to thank the Alabama Division of Wildlife and Freshwater Fisheries
Division, Montgomery, AL for funding this project. We would also like to thank the following
individuals for volunteering their time and effort in the field to help locate sites
and dig burrows: Carl Couret (US Fish and Wildlife, Daphne, AL); Bill Finch (The Nature
Conservancy, Mobile, AL); John Johansen (Tulane University, New Orleans, LA);
Dan Jones (Clemson University, Clemson, SC); Ben Raines (Mobile Register, Mobile,
AL); and B. Starling (Mobile Register, Mobile, AL).
Fitzpatrick, J.F., Jr. 1978. A new burrowing crawfish of the genus Cambarus from southwest
Alabama (Decapoda, Cambaridae). Proceedings of the Biological Society of
Fitzpatrick, J.F., Jr. 1991. Determination of the current status of the rare crawfish Cambarus
(Lacunicambarus) miltus Fitzpatrick. Report to the US Fish and Wildlife Service,
Jackson, MS. 6 pp.
Hartfield, P. 1991. Status review of the crayfish Cambarus miltus. US Fish and Wildlife
Survey, Jackson, MS. 3 pp.
Taylor, C.A., M.L. Warren, Jr., J.F. Fitzpatrick, Jr., H.H. Hobbs III, R.F. Jezerinac, W.L.
Pflieger, and H.W. Robison. 1996. Conservation status of the crayfishes of the United
States and Canada. Fisheries 21:25–38.
Taylor, C.A., G.A. Schuster, J.E. Cooper, R.J. DiStefano, A.G. Eversole, P. Hamr, H.H.
Hobbs, III, H.W. Robison, C.E. Skelton, and R.F. Thoma. 2007. A reassessment of the
conservation status of the crayfishes of the United States and Canada after 10+ years
of increased awareness. Fisheries 32:372–389.
Welch, S.M., and A.G. Eversole. 2007. GIS-based analyses of freshwater crayfish in the
Conecuh National Forest, Alabama. Final Report to National Forests in Alabama,