![[Cambarus bartonii]](ffodiens.jpg)
Fallicambarus fodiens
Digger Crayfish
DESCRIPTION
This species has no official
common names, but is sometimes referred
to as Chimney or Digger crayfish. It is a
medium-sized, obligate burrowing,
semi-terrestrial crayfish, distinguished from
similar species (Devil Crawfish) by presence
of notch on movable finger of chela.
Colouring is uniform light brown to rust or
red-olive brown with darker mottling.
HABITAT
A semi-terrestrial burrower. The Chimney Crayfish spends most of its life within burrows
consisting of a network of tunnels.
DISTRBUTION
Canada/Ontario
Canada/OntarioÐ This
species is the only representative of its genus
occurring in Canada where it is at the
extreme northern edge of its range. It is
restricted to southern Ontario where it
occurs from south of Lake Simcoe and west of
Lake Scugog to Lake St. Clair and the Detroit
River (Crocker and Barr, 1968; Hamr unpublished
data; Guiasu et al., 1996; Barr, 1996).
North America Ð The Chimney Crayfish is
widely distributed in the east and midwest
of North America. It is found in
Ontario, Michigan, Ohio,
Illinois, Indiana, West
Virginia, Maryland, Alabama,
Georgia, Florida as well as west to
Missouri, Arkansas, Louisiana,
Oklahoma and Texas (Page, 1985;
Hobbs Jr. and Robinson, 1989).
ECOLOGY
The
burrows have as many as four entrances
and a large terminal chamber which is
usually located below the groundwater table.
The entrances are usually made conspicuous
by tall "chimneys" constructed from pellets
of excavated mud. Chimney Crayfish burrows
are found in wetlands (marshes and swamps)
but also along roadside ditches and creek
banks in moist clay, among rooted semi
aquatic plants and grasses. Burrowing
activity appears to be the greatest in the
spring and following periods of heavy
rainfall, in order to repair damaged burrows
(Williams, 1974). Excavation is also increased
as the water table drops and crayfish burrow
to greater depths to reach ground water.
This species needs primarily clay soils in
order to burrow (Crocker and Barr, 1968)
and thus the hard rocks and thin soils of the
Canadian Shield may limit the availability of
suitable habitats and northward range
expansion. The burrows of this species may
have water with low oxygen concentrations
(8-12% saturation) (Williams et. al., 1974)
and adults can survive for prolonged
periods (up to several weeks) out
of water if the humidity of the
air is high enough. The
Chimney Crayfish has never
been found together with Devil
Crawfish in Canada (Guiasu et
al., 1996) but it does occur
together with Papershell Crayfish
in roadside ditches and wetlands
in southwestern Ontario
(Hamr, unpublished data).
LIFE HISTORY
In Ontario, reproduction
appears to take place from spring to fall.
Mature females show strong glair gland
development from April to August.
Copulation has been observed in October in
the wild and late April to early June in
captivity. Females with eggs are found from
June to August and with young from July to
September. Eggs and young are therefore
carried into autumn and there is evidence
that some females may over winter with
attached eggs or young and release them
(and then moult) the following summer
(MacManus, 1960b; Hamr, 1983). Hatching
occurs between July and August and the
young undergo two moults in their
metamorphosis, spending about 15 days
attached to their mothers. Free-living young
measuring about 5 mm (0.195 in.) CPL are
first found in August (Hamr, and Berrill, 1985).
Moulting in immature crayfishes take place
form May to early October and maturity is
reached at about 2 years of age. Adult males
moult in July and September. Moulting into
both Form I and Form II at the same time of
year has been observed (Hamr and Berrill,
1985). Mature females moult once following
the reproductive season but the timing of
moult is variable (September or the
following June-July) depending on local
conditions. The average life-span appears to
be 3 years old and the maximum life-span is
4 years. The maximum recorded size is 39
mm (1.52 in.) CPL from a male collected in
Rawdon, Quebec. Sexual dimorphism with
respect to chela length between sexes and
Form I and From II males is present but not
as pronounced as in the Orconectid
crayfishes (Hamr and Berrill, 1985).
CONSERVATION STATUS
Populations of
Chimney Crayfishes are scattered over a
wide geographic area but are never locally
common and are restricted to isolated
patches of wetland habitat, usually in the
midst of extensive agricultural and urban
areas. The amount of available habitat
suitable for Chimney Crayfishes is
decreasing. The species range coincides
with heavily urbanized and industrialized
areas (Barr, 1996) as well as the center of
most of Ontario's agricultural production.
Guiasu et al., (1996), found that several of
the Toronto locations reported by Crocker
and Barr (1968), which had Chimney
Crayfish colonies in the early and mid-
1960s, have since been developed for
industrial or commercial purposes.
Similarly, areas within the jurisdiction of
the Metropolitan Toronto and Toronto
Region Conservation Authority, which also
used to support Chimney Crayfish
populations, have now become unsuitable
for these crayfish, due to urban
development (Guiasu et al. 1996). Therefore,
there is sufficient evidence to suggest that
Chimney Crayfish is "Vulnerable' in
Ontario, as the probability of habitat
destruction and thus local extinctions is
high throughout the vast majority of its
range (Hamr, 1998).
(Used by permission: text by Premek Hamr, modified from "Baitfish of North America"2007
painting by Aleta Karstad)
|