Pelobatidae
Scaphiopus bombifrons Plains Spadefoot
Spadefoots differ from true toads,
genus bufo, in that they have a nearly smooth,
obviously
moist skin and lack the distinct parotoid glands typical of toads.
They are usually called "spadefoot
toads"
because of the digging tubercle on each hind foot and their
squatty,
toad-like
shape. Spadefoots are brown
or
gray,
usually
with a few rust-colored dorsal nodules.
They
have a
single black (not brown) wedge-shaped spade on each back foot.
This device permits rapid digging in sandy or
loess
soils.
Spadefoots also have vertically
elliptical pupils
(cat eyes) instead of the round pupils typical of
most
frogs, or the horizontally elliptical pupils characteristic of
toads. One needs to examine the eye in fairly bright light to
see this difference.
Plains spade foots
have a bump on the forehead between the eyes.
The skin secretions
of true
toads are toxic to many animals that might eat them,
but only a few (none from Iowa) are dangerous
for humans to handle.
However,
spadefoots do have skin
secretions that may produce severe allergic reactions,
even
initiation
of asthma attacks in some people.
The
toad-like,
squatty
shape of
spadefoots easily
distinguishes
them
from our
frogs,
and the pupil shape, lack of cranial ridges, and lack of
distinct parotoid
glands separate them from toads.
Toads have two brown digging structures on each back
foot rather
than
a single black spade. Our spadefoots range up to 2 1/8
inches (54 mm) in length.
There
are no recognized subspecies of S. bombifrons.
Plains spade foots breed in Iowa in late May, June or July after
heavy rains that fill their ephemeral breeding pools. The call
is a loud, toneless quack, more like the call of Woodhouse's
toad than any other Iowa species.
Spadefoots live most of their lives underground, coming to the
surface during heavy rains and periods of high humidity. They
are highly adapted for survival in arid environments and their
tadpoles are known to be cannibalistic, enabling them to
concentrate protein and thyroxin for rapid growth and prompt
metamorphosis in a rapidly drying pool.
Scaphiopus bombifrons
has a wide distribution on the Great Plains from southern Canada
to northern Mexico. It was first discovered in the loess hills
of western Iowa in 1959, leading us to suspect that it has only
recently dispersed into the state. Thus far, it is limited to
the western tier of counties where it breeds high in the hills,
often in temporary roadside pools. The species is abundant in
all these counties except the northern two. Encroaching forest
may threaten their survival in some areas.