The ant-eating frog is one of the smallest species of vertebrates on the
University of Kansas Natural History Reservation, but individually it is
one of the most numerous. The species is important in the over-all
ecology; its biomass often exceeds that of larger species of
vertebrates. Because of secretive and subterranean habits, however, its
abundance and effects on community associates are largely obscured.
The Reservation, where my field study was made, is the most northeastern
section in Douglas County, Kansas, and is approximately 5-1/2 miles north
and 2-1/2 miles east of the University campus at Lawrence. The locality
represents one of the northernmost occurrences of the species, genus,
and family. The family Microhylidae is a large one, and most of its
representatives are specialized for a subterranean existence and a diet
of termites or ants. The many subfamilies of microhylids all have
distributions centering in the regions bordering the Indian Ocean, from
South Africa and Madagascar to the East Indies, New Guinea, and
Australia (Parker, 1934). Only one subfamily, the Microhylinae, is
represented in the New World, where it has some 17 genera (de Carvalho,
1954) nearly all of which are tropical. _G. olivacea_, extending north
into extreme southern Nebraska (Loomis, 1945: 211), ranges farther north
than any other American species. In the Old World only _Kaloula
borealis_ has a comparable northward distribution. Occurring in the
vicinity of Peiping (Pope, 1931: 587), it reaches approximately the same
latitude as does _Gastrophryne_ in Nebraska. The great majority of
microhylid genera and species are confined to the tropics.
Nearly all ant-eating frogs seen on the Reservation have been caught and
examined and individually marked. By November 1, 1954, 1215 individuals
had been recorded with a total of 1472 captures. In the summer of 1950,
Richard Freiburg studied this frog on the Reservation and his findings
(1951) led to a better understanding of its natural history. The
numbers of frogs studied by him however, were relatively small and the
field work was limited to the one summer. The data now at hand,
representing six consecutive years, 1949 through 1954, serve to
supplement those obtained by Freiburg, corroborating and extending his
conclusions in most instances, and also indicating that certain of his
tentative conclusions need to be revised.
While the present report was in preparation, Anderson (1954) published
an excellent account of the ecology of the eastern species _G.
carolinensis_ in southern Louisiana. Anderson's findings concerning this
closely related species in a much different environment have been
especially valuable as a basis for comparison. The two species are
basically similar in their habits and ecology but many minor differences
are indicated. Some of these differences result from the differing
environments where Anderson's study and my own were made and others
certainly result from innate genetic differences between the species.
The frog with which this report is concerned is the _Microhyla
carolinensis olivacea_ of the check list (Schmidt, 1953: 77) and recent
authors. De Carvalho (1954: 12) resurrected the generic name,
_Gastrophryne_, for the American species formerly included in
_Microhyla_, and presented seemingly valid morphological evidence for
this plausible generic separation.
_G. olivacea_ is obviously closely related to _G. carolinensis_; the
differences are not greater than those to be expected between well
marked subspecies. Nevertheless, in eastern Oklahoma and eastern Texas,
where the ranges meet, the two kinds have been found to maintain their
distinctness, differing in coloration, behavior, calls, and time of
breeding. Hecht and Matalas (1946: 2) found seeming intergrades from the
area of overlapping in eastern Texas, but some specimens from this same
area were typical of each form. Their study was limited to preserved
material, in which some characters probably were obscured. More field
work throughout the zone of contact is needed. The evidence of
intergradation obtained so far seems to be somewhat equivocal.
Besides _G. olivacea_ and typical _G. carolinensis_ there are several
named forms in the genus, including some of doubtful status. The name
_mazatlanensis_ has been applied to a southwestern population, which
seems to be a well marked subspecies of _olivacea_, but as yet
_mazatlanensis_ has been collected at few localities and the evidence of
intergradation is meager. The names _areolata_ and _texensis_ have been
applied to populations in Texas. Hecht and Matalas (1946: 3) consider
_areolata_ to be a synonym of _olivacea_, applied to a population
showing intergradation with _carolinensis_, but Wright and Wright (1949:
568) consider _areolata_ to be a distinct subspecies. _G. texensis_
generally has been considered to be a synonym of _olivacea_. Other
species of the genus include the tropical _G. usta_, _G. elegans_ and
_G. pictiventris_.
Of the vernacular names hitherto applied to _G. olivacea_ none seems
appropriate; I propose to call the species the Kansas ant-eating frog
because of its range extending over most of the state, and because of
its specialized food habits. The type locality, originally stated to be
"Kansas and Nebraska" (Hallowell, 1856: 252) has been restricted to Fort
Riley, Kansas (Smith and Taylor, 1950: 358). Members of the genus have
most often been referred to as toads rather than frogs because of their
more toadlike appearance and habits. However, this family belongs to the
firmisternial or froglike division of the Salientia and the terms "frog"
and "toad," originally applied to _Rana_ and _Bufo_ respectively, have
been extended to include assemblages of related genera or families.
Members of the genus and family usually have been called
"narrow-mouthed" toads from the old generic name _Engystoma_, a synonym
of _Gastrophryne_. _G. olivacea_ usually has been referred to as the
Texas narrow-mouthed toad, or western narrow-mouthed toad. The latter
name is inappropriate because the geographic range is between that of a
more western representative (_mazatlanensis_) and a more eastern one
(_carolinensis_). The names _texensis_, _areolata_ and _carolinensis_
have all been applied to populations in Texas, and it is questionable
whether typical _olivacea_ even extends into Texas.