Florida Entomologist 84(4)
GRYLLUS CAYENSIS N. SP. (ORTHOPTERA: GRYLLIDAE),
A TACITURN WOOD CRICKET EXTIRPATED FROM THE FLORIDA KEYS:
SONGS, ECOLOGY AND HYBRIDS
THOMAS J. WALKER
Dept. Entomology & Nematology, University of Florida, Gainesville, FL 32611-0620
Gryllus cayensis, new species, formerly occurred in tropical hammocks in the Florida Keys
but has not been found there since 1972, the initial year of aerial spraying of north Key
Largo hammocks for mosquito control. It is now known only from pineland in Everglades
National Park. Males of G. cayensis make no ordinary calling songs, but some caged males
occasionally produce soft 3-4 pulse chirps with a principal frequency of nearly 11 kHz. Males
of its sister species, G. fultoni (Alexander), which occurs in north Florida, call with loud 2-4
pulse chirps with a principal frequency of about 4.5 kHz.
Key Words: Gryllus cayensis, Gryllus fultoni, calling song, hybridization, phylogeny
Se describe una nueva especie, Gryllus cayensis, la cual solia existir en los "hammocks" tro-
picales de los Cayos de la Florida, pero que no se ha encontrado alli desde 1972, ano en que
se inicio la aspersi6n area en el norte de Cayo Largo para el control de mosquitos. Hoy en
dia solamente en los bosques de pinos del Parque Nacional de los Everglades. Los machos de
G. cayensis no hacen llamados normales de canciones, pero algunos machos enjaulados oca-
sionalmente produce chirridos suaves de 3-4 pulsos con una frecuencia principal cercana a
los 11kHz. Los machos de una especie hermana, G. fultoni (Alexander), la cual ocurre al
norte de la Florida, hacen llamados con un fuerte chirrido de 2-4 pulsos con una frecuencia
principal de aproximadamente 4.5 kHz.
Most crickets of the genus Gryllus are known
as field crickets because they occur in fields and
other open habitats. However, three of the nine
species known from eastern United States live in
woods: G. vernalis Blatchley, the northern wood
cricket; G. fultoni (Alexander), the southern wood
cricket; and G. ovisopis Walker, the taciturn wood
cricket. In this paper, I describe a species that oc-
curs in woods in Florida south of Miami. It differs
from G. fultoni, its closest relative, in morphology,
life cycle, song, and mitochondrial DNA. Gryllus
cayensis and G. fultoni produce fertile hybrids in
Gryllus cayensis Walker, New Species
Keys Wood Cricket, Fig. 1
HOLOTYPE.-Male, Florida: Monroe Co.,
north Key Largo, Sec. 26, T59S, R40E, 23-VIII-
Aug. 1958, T. J. Walker, leaf litter in tropical ham-
mock, deposited in Florida State Collection of Ar-
thropods (FSCA). Body black; legs and cerci
reddish brown; dorsal field of tegmina brownish
black; lateral field paler except at rear. Length of
body, 20 mm; pronotal length x width, 4.2 x 5.8;
length of tegmen, 7.6; length of hind femur, 13.1.
Hind wings about half as long as tegmina.
ALLOTYPE.-Female, same data as holotype.
Coloration like holotype but slightly paler.
Length of body, 21 mm; pronotal length x width,
5.0 x 6.5; length of tegmen, 8.5; length of hind fe-
mur, 14.3; length of ovipositor, 14.8.
PARATYPES.-122 males [M], 120 females [F].
FSCA: Florida, Monroe Co., Florida Keys, Key
Largo, 3 M (1 reared from juvenile), 1 F, same data
as holotype; 1 M reared from juvenile, tropical ham-
mock, 9-VIII-1972, T. J. Walker [TJW]; 10 M, 4 F,
progeny of previous male and a female with same
data; Sugarloaf Key, 1 F reared from juvenile, ham-
mock litter, 24-VI-1964, TJW and R. E. Love; Big
Pine Key, 1 F, 9-IV-1948, collector unknown. Dade
Co., Everglades National Park, Long Pine Key, pine-
land, 1 M, 1 F, 19-VIII-1978, TJW; 1 M, 3 F (reared
progeny of 1 F coll. 19-VIII-1978); 2 M reared from
juveniles, 6 F, 22-23-IX-1980, Robert Sullivan; 31 M,
47 F (reared progeny from 5 F coll. 22-23-IX-1980);
1 M, 2 F, 13-VII-1988, TJW; 72 M, 52 F (reared prog-
eny of 2 F coll. 13-VII-1988). University Michigan
Museum of Zoology [UMMZ]: Florida, Dade Co., 6
mi e. Paradise Key [now Royal Palm Hammock], 2
F, pineland, 19-X-1929, T. H. Hubbell.
Six male and six female reared paratypes from
those listed above were sent to UMMZ, U. S. Na-
tional Museum, Philadelphia Academy of Natural
Science, and California Academy of Science.
Walker: Gryllus cayensis, A Taciturn Wood Cricket
Fig. 1. Drawing of holotype male of Gryllus cayensis. Color photographs of living paratypes are accessible from
the online version of this article at http://www.fcla.edu/FlaEnt/.
Florida Entomologist 84(4)
Four species of Gryllus occur in extreme south
Florida: G. assimilis (Fabricius), G. cayensis, G.
firmus Scudder, and G. rubens Scudder. G. cayen-
sis is the only one of the four that has any of the
following features: reddish brown hind femora,
tegmina (measured in situ) shorter than two
pronotal lengths, inhabits woods. It is always mi-
cropterous, whereas the others are either dimor-
phic in wing length (G. firmus and G. rubens) or
always macropterous (G. assimilis). G. fultoni, a
wood cricket occurring north of the range of
G. cayensis and similar to it in many respects, has
tegmina that are at least twice the length of the
pronotum. The stridulatory files of two males
from Key Largo had 110 and 100 teeth and were
2.74 and 2.26 mm long respectively. This makes
them indistinguishable from the files ofG. fultoni
(Nickle and Walker 1974).
In the field, males of most Gryllus species are
easy to identify and to locate by their loud, persis-
tent, species-specific calling songs. However,
G. cayensis has never been heard to call in the
field. Most males in captivity make no sounds
when alone, although a few make soft chirps
rarely. Only one of five males collected on Key
Largo in 1958 was ever heard to stridulate while
alone. The soft chirps were tape recorded but the
tape was loaned and lost. A male reared from a
Key Largo juvenile collected in 1972 was kept for
16 days where it could be monitored for calling
during the night and at dawn (my bedroom). It
was never heard to stridulate. That male and his
consort (also reared) produced eight males that
were likewise kept in individual cages in my bed-
room. Of four males monitored for 2 weeks, two
were never heard, one was heard twice but was
too wary to tape, and one produced soft chirps reg-
ularly at dawn and was tape recorded. Three of
the other males were monitored for 1 week and
one was monitored for 4 weeks. None of these was
I used CoolEdit 2000 (Syntrillium Software) to
analyze the one extant recording of solitary strid-
ulation by G. cayensis (Walker Tape Library
[WTL] tape 475-2; 22.0C). Three- and 4-pulsed
chirps were produced at a rate of ca. 2.4/s. The
pulse rate within the chirps was ca. 33 pulses/s.
The principal frequency of the pulses was 10.8
kHz with secondary strong frequencies between 6
and 9 kHz. The chief difference between the rare,
soft song of G. cayensis and the common, loud
song of G. fultoni is that the song of the latter spe-
cies has a principal frequency of ca. 4.5 kHz.
Males of G. cayensis from Long Pine Key were
also taciturn. Of 24 males reared from females
collected 22-23 Sept 1980 and monitored for a
week or more in my bedroom, only one was heard.
It occasionally produced soft chirps, but not for a
The only other Gryllus known to lack a conven-
tional calling song is G. ovisopis (Walker 1974).
Like G. cayensis, it is flightless and occurs in per-
manent, woodland habitats. In keeping with their
lack of calling, both species have reduced tegmina
(tegminal length less than twice that of the prono-
tum). However, males of Gryllus insularis Scud-
der have tegmina that are approximately as short
(ca. 1.9 times the length of the pronotum), yet
they produce a typical Gryllus calling song (D. B.
Weissman, pers. comm.).
An aspect of calling that is not generally ap-
preciated is that songs carry poorly between
sender and receiver if both are at ground level.
Michelsen (1985) calculated that [field] crickets
might be able to hear each other on the ground
only at distances less than 1 to 2 m. On the other
hand, if sender or receiver (or both) is above
ground level, transmission is much improved.
Thus a cricket flying above a calling male can
hear its call at a much greater distance than can
a ground-level cricket. That flying crickets hear
and respond to songs coming from the ground can
be demonstrated with sound-baited traps that
catch only flying crickets. For example, thousands
of Gryllus rubens Scudder and hundreds of Gryl-
lus firmus Scudder flew into 1.4 m diameter fun-
nels baited with broadcasts of synthetic calls
(Walker 1986). The only way that a male can
broadcast to distant, ground-level females is to
call from a perch. Males of the two large, ground-
living, woods-inhabiting, non-taciturn crickets in
north Florida often do just that. Gryllus fultoni
and Anurogryllus arboreus Walker males often
call from 0.5 to 2 m above ground level by ascend-
ing tree trunks (Paul and Walker 1979). Females
of these two species are always flightless. A disad-
vantage of calling from tree trunks is greater
exposure to acoustically orienting predators
(Walker 1964). In fact a disadvantage of calling
from anywhere is that some predators and para-
sitoids find prey by homing on their calling songs
(Burk 1982; Walker 1993). Loss or reduction of
calling should be most likely in crickets that are
flightless, live in permanent, dense populations,
and are plagued by acoustically orienting preda-
tors and parasitoids. G. cayensis probably met at
least the first two of these criteria when it lost its
long-range calling song and reduced its solitary
Although males of G. cayensis seldom stridu-
late while alone, they readily produce courtship
songs when they encounter a female. The reared
1972 Key Largo male that remained silent for 16
days in my bedroom, almost immediately used
song to court an introduced female. This was re-
corded (WTL 475-1; 26.2C) and found to consist
of groups of 3 to 10 pulses often followed by a tick.
Walker: Gryllus cayensis, A Taciturn Wood Cricket
The pulse rate within the groups was ca. 57
pulses/s, and the group rate was ca. 5/s. The
strongest frequency of the pulses was 5.6 kHz and
of the ticks, 15.8 kHz.
Ten-second samples of the courtship and call-
ing songs (WTL 475-1 and 2) were digitized and
saved as .wav files. These are accessible from the
online version of this article at http://www.fcla.
Distribution, Ecology, and Seasonal Life Cycle
G. cayensis is known only from tropical ham-
mocks in the Florida Keys and from pinelands
south of N lat 25.4 in Dade Co., Florida. The
southernmost Florida records for G. fultoni are
Marion and Volusia Counties; for G. ovisopis,
Lake Placid and Punta Gorda. Thus G. cayensis is
geographically isolated by more than 350 km
from G. fultoni and by more than 200 km from
The seasonal life cycle of G. cayensis has not
been studied in the field, but laboratory rearing,
weather records, and collecting records provide
clues. In the laboratory at 25C and 16L:8D pho-
toperiod, development from egg to adult requires
about 6 months. Eggs of field-collected adults
hatched in about 4 weeks under these conditions.
There was never delayed hatch as with the eggs of
Gryllus species that produce all diapause eggs or
mixtures of diapause and nondiapause eggs
(Walker 1980). Average temperatures at Key
West and Miami are above 25C from May
through October and below 25C from November
through April (USDC 1933, 1960). Adults of
G. cayensis have been collected in April, July,
August, and September; late juveniles in June,
July, August, and September; and one early juve-
nile was collected in August. (Juveniles were
reared to adults prior to identification.)
These temperatures and collecting records do
not preclude G. cayensis from breeding continu-
ously, with all stages occurring at all times. How-
ever, the Keys and adjacent mainland Florida
have a winter and spring dry season that lasts
from November through April. On average, less
than 25% of the yearly rainfall occurs during this
six-month period (Homestead, Flamingo, and
Long Key stations; USDC 1960). During the hot
days of April and early May, before the rains start,
drought often becomes severe and Gryllus
hatchlings would probably not survive. If the dry
season prevents continuous breeding, large
nymphs or diapausing adults would be the ex-
pected late dry-season stages, because they have
the most favorable surface-to-volume ratios. These
could become reproductively active adults in antic-
ipation of, or in response to, the start of summer
rains. The progeny of these adults would become
adults in late summer, which, in turn, would lay
eggs that would produce the large nymphs or dia-
pausing adults required to survive the dry season.
Eggs laid in the dry season would either not hatch
or produce nymphs that would desiccate.
Rearing and Experimental Crosses
Because the Keys were distant and specimens
of G. cayensis were difficult to collect, I brought
live specimens to Gainesville for further study
and for increase through rearing.
Some 85% of the paratypes of G. cayensis are
reared progeny of females collected as they fed at
trails of oatmeal laid in the pineland of Long Pine
Key. In 1978, 1980, and 1988, I obtained a total of
206 adults from eight field-collected females.
On 9 Aug 1972, I captured two mid-sized juve-
niles at oatmeal trails in hammocks on Key
Largo. I reared the two under an open shelter in
Gainesville and obtained an adult male and fe-
male by 26 September. The pair mated by 1 Octo-
ber and the first eggs hatched 5 Nov 1972. The
female was deprived of her consort on 29 Oct (for
pinning) but continued to lay fertile eggs until she
died in mid-December. Throughout her oviposi-
tion, I attempted to rear cohorts of her progeny in
the field and in the laboratory at 25C and 16L:8D
photoperiod. Under field conditions, none of 200
juveniles survived beyond the first few stadia. Ju-
veniles that hatched in the field in early or mid-
November died in about one month; early juve-
niles transferred to the field from the laboratory
in mid-December and mid-January lasted longer
but none reached the middle stadia and none sur-
vived as long as three months. When many juve-
niles died at once in the jars in the field, they
appeared to succumb to a white mold. Under lab-
oratory conditions, about 400 early juveniles sur-
vived to the middle stadia with low mortality, but
then their numbers declined week after week. At
the same time a few of the juveniles became much
larger than their sibs as they reached the final ju-
venile stadia. This suggested cannibalism, as did
finding partially eaten crickets. I therefore di-
vided each laboratory cohort among two or three
rearing containers and succeeded in rearing 30
adults. Most of the adults were used in experi-
mental crosses with G. fultoni and G. ovisopis, the
two wood crickets that occur in Florida north of
the range ofG. cayensis.
All G. fultoni and G. ovisopis used in experi-
mental crosses were second laboratory generation
crickets from stock collected in Alachua County,
Florida. Five replicates of these four crosses were
set up in the spring of 1973 as appropriate crick-
ets matured: cayensis x cayensis, cayensis x ful-
toni, fultoni x cayensis, and ovisopis x cayensis
(male parent listed first). Because of a shortage of
crickets, only four replicates ofcayensis x ovisopis
and one replicate each offultoni x fultoni, and ovi-
sopis x ovisopis were established. Neither the C x
O nor 0 x C crosses produced progeny. All other
Florida Entomologist 84(4)
types of crosses produced progeny: C x C (4 of 5
replicates), C x F (4 of 5), F x C (3 of 5), F x F (1 of
1), Ox O (1 of 1).
Two F, males of the C x F cross were monitored
for calling for one month in my bedroom. Neither
was ever heard.
No further crosses were set up, but the prog-
eny from one of the C x F crosses produced numer-
ous F2 hatchlings from which seven males and a
female were reared. The males were monitored
for calling and the songs of four were tape re-
corded (WTL 475 x 484-1, 2, 4, 5; 20.0-22.2C).
The chirp rate was ca. 2.0/sand the principal fre-
quency was ca. 5.0 kHz. The songs were reminis-
cent ofG. fultoni though weaker.
Phylogeny and Species Status
Results of the laboratory crosses indicated
that G. cayensis was more closely related to G. ful-
toni than to G. ovisopis. They did not prove that
G. cayensis and G. fultoni were conspecific, be-
cause species of Gryllus that fail to hybridize
where they occur together in the field often pro-
duce fertile hybrids in the laboratory. For exam-
ple, in no-choice, laboratory crosses G. rubens will
hybridize with G. assimilis and with G. texensis
Cade and Otte, species with which G. rubens lives
in south Florida and west Florida respectively
(Bigelow 1960; Walker 2000).
North American Gryllus have been used for
numerous comparative studies of physiology, be-
havior, and ecology. Such studies have been ham-
pered by the lack of a consensus phylogeny of the
species. Molecular techniques now promise to
provide one. Harrison and Bogdanowicz (1995)
studied the mitochondrial DNA restriction site
maps for eight Gryllus species from eastern North
America, including the six that occur in peninsu-
lar Florida. They concluded that G. cayensis and
G. fultoni were sister species and that G. veletis
(Alexander and Bigelow) and one or more uniden-
tified Gryllus species from western U.S. were a
sister group to the G. fultonilG. cayensis group.
Gryllus ovisopis (the other taciturn wood cricket),
G. pennsylvanicus Burmeister, and G. firms
formed a distinct group, well separated from the
G. c.,'.. -... G. fultonilG. veletis group. The se-
quence divergence between G. cayensis and G. ful-
toni was much greater than that between G.
ovisopis and either G. firmus or G. pennsylvanicus
(0.027 vs. 0.002-0.010), which adds to the evi-
dence that G. cayensis merits species status.
[Note: The two G. cayensis used by Harrison and
Bogdanowicz were from Long Pine Key (19 Aug
1978) rather than from Key Largo.]
Huang et al. (2000) expanded the mt DNA da-
tabase for North American Gryllus to include
three more U.S. species and the complete cyto-
chrome b gene and a portion of the 16S rRNA
gene. They did not include G. cayensis, but other-
wise confirmed the relationships reported above,
while adding G. integer (from California) to the
G. veletis/G.fultoni[/G. cayensis] clade.
The origin ofG. cayensis and G. fultoni from a
common ancestral species seems likely to have oc-
curred when Pleistocene fluctuations in sea levels
isolated south Florida woods and wood crickets
from north Florida ones. Some crickets that occur
in tropical south Florida apparently got there by
flying or rafting from Cuba; however, G. cayensis
is flightless, and rafting seems unlikely since the
eggs are laid in soil. Zayas (1974) makes no men-
tion of a Cuban counterpart to G. cayensis.
Probable Extirpation from the Florida Keys
My first experience with G. cayensis was at
mid-morning, 23 August 1958, when I observed
numerous individuals in the leaf litter of a tropi-
cal hammock on north Key Largo. I easily col-
lected five adults and a large nymph. Since then,
I've collected only three individuals in the Keys:
one nymph from hammock leaf litter on Sugarloaf
Key in June 1964 and two nymphs feeding at a
trail of oatmeal laid in a hammock on north Key
Largo, 9 Aug 1972. (Oatmeal was dribbled as a
trail shortly after sunset and the trail was repeat-
edly searched with a light during the first half of
the night.) On 1 and 2 June 1973, I got no speci-
mens from oatmeal trails through the hammock
that was successfully searched in 1972. On 5 Aug
1987, I found no specimens along oatmeal trails
laid in two hammock areas near where I'd first
found G. cayensis in 1958. On 6 Aug 1987 and 12
Jul 1988 I unsuccessfully searched three oatmeal
trails laid on Big Pine Key. The 1987 trail was in
hammock and pineland. The two 1988 trails were
in Watson's and Cactus Hammocks.
The failure to collect G. cayensis along oatmeal
trails in the Florida Keys from 1973 forward con-
trasts with the success of the same technique on
the mainland. Each time oatmeal trails were laid
in the pineland of Long Pine Key, three or more
individuals were collected: 16 Aug 1978 (n = 3), 22
and 23 Sept 1980 (n = 8), 13 Jul 1988 (n = 5).
The most likely cause of the apparent disap-
pearance of G. cayensis from the Florida Keys is
aerial and ground application of insecticides by
the Monroe County Mosquito Control District.
Fogging with truck-mounted units began in 1951
and aerial spraying began in 1962. However, until
1967, all applications were in the well-populated
parts of the Keys from mid Key Largo south. In
that year the District began malathion fogging of
north Key Largo from trucks. In 1972 they
switched to ultra low volume application of 93%
fenthion (Baytex) from trucks and aerial applica-
tion of 4% naled (Dibrom) from DC-3 aircraft
The switch to organophosphate insecticides
and to aerial spraying thus coincided with the ap-
Walker: Gryllus cayensis, A Taciturn Wood Cricket
parent disappearance of G. cayensis from north
Key Largo. Several lines of evidence suggest, but
do not prove, that the spraying caused the disap-
pearance. First, organophosphate insecticides are
nonspecific and highly toxic (Matsumura 1985).
Second, when I sought G. cayensis on Key Largo in
1973, I noted that there were no crickets calling in
the hammocks. This was strange because on all
previous visits to hammocks in the Keys the tin-
kling chirps of Cyrtoxipha gundlachi Saussure
had been heard in abundance. Thirdly, the popula-
tion history of Papilio ponceanus Schaus (Schaus'
swallowtail) on north Key Largo supports the con-
tention that mosquito control had lasting effects
on nontarget insects. Papilio ponceanus once oc-
curred throughout the Keys and adjacent main-
land Florida but by 1976 was officially classed as
"threatened" and by 1984 as "endangered" (Em-
mel 1995). Through 1972 it was commonly seen
and collected on north Key Largo. From 1973
through the mid 1980s, it was rare or missing
(Emmel 1995). Studies of the toxicity of fenthion
and naled to Papilio cresphontes Cramer (a stand-
in for P. ponceanus) showed that the concentra-
tions sprayed on the hammocks of Key Largo were
at least 400 times greater than the LC-50 for
P. cresphontes (Eliazar 1992; Emmel 1994).
When spraying of north Key Largo hammocks
ended, in the mid 1980s,P. ponceanus began to re-
turn, probably by immigration from Old Rhodes,
Elliott and smaller keys in Biscayne National
Park. On these keys, which were never sprayed,
P. ponceanus populations were continuously
present. The same keys may be home to perma-
nent populations of G. cayensis, unless, perhaps,
they were eliminated by the saltwater storm
surge that temporarily covered them during Hur-
ricane Andrew's assault in August 1992.
Unlike P. ponceanus, G. cayensis is flightless. If
G. cayensis has been eliminated from Key Largo,
it is unlikely to reestablish soon even if abundant
populations exist on Old Rhodes and Elliott Keys.
Thanks go to Harry McVay for making the drawing,
to Tom Emmel for help with the Schaus' swallowtail lit-
erature, to David Weissman and James Lloyd for im-
proving the manuscript, and to NSF for grants that
made possible some of the work reported here. This re-
search was supported by the Florida Agricultural Ex-
periment Station, and approved for publication as
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