SUMMARY: COQUI BIOLOGY AND CONTROL IN VOLCANO
Coqui vary greatly in color from brown, tan, to yellow (and even red or black), with or without a stripe down
the back, and occasionally with stripes on the sides of body or head.
Females are much larger than males. Males call loudly; females have a softer rasping call to
defend territory. Calls usually start with a "warm up" repetition of the first note,
"ko," a territorial call to other males, and then the characteristic "kee"
call to attract females.
Visit the HEAR website
to hear the range of calls coqui make. Coqui are reported to live 4-6 years and continue to increase in size
as they age. It is not surprising then that island coqui seem to be getting bigger, now that they have
been on the island for over 10 years. Coqui are similar in appearance to the greenhouse frogs,
only much larger. The call of the greenhouse frog is much quieter and has been characterized as
a "cricket-like chirping." Check the CTAHR website
for a detailed comparison between the two closely related frogs, both accidentally introduced to Hawaiʻi.
Coqui eggs are fertilized internally. This implies that "pregnant" females can be
transported to Volcano and produce young.
Coqui frogs reach their highest populations densities in wet,
heavily vegetated lowland areas. In forested areas of lower Puna there are found as many as
with 2,000 adults/acre. This is approximately twice the density of coqui, on average, in its native range in
Coqui do not have a swimming tadpole stage and thus do not
require standing water to reproduce. Reproduction can take place in a forested environment without streams
or ponds. A clutch of 15-40 eggs is typically laid in a rolled over leaf, or in moss, leaf litter, and
other protected sites (e,g, old cars). Eggs are brooded by the males to keep them moist.
Under laboratory conditions in Hawai`i, mating pairs can produce a new clutch of eggs every
2 ½ weeks or 1,400 eggs per year. It takes about 14-17 days for eggs to hatch out into tiny froglets.
Froglets reach maturity and reproduce in about eight months. In the cooler temperatures of Volcano,
maturation of eggs and froglets is undoubtedly slower.
Eggs and froglets have been observed in
Royal Hawaiian Estates and inferred from size of populations in some sites in Hawaiian Orchid Isle Estates.
Eggs, but no froglets, have been seen to date in Mauna Loa Estates and Volcano Village.
So far, no eggs or froglets have been found in Volcano Golf Course. This absence could reflect a
combination of effective control efforts, incomplete searching, or temperature-delayed
A recent study of potential coqui predators in Hawai`i, including black rats, Polynesian rats,
cane toads, and mongoose, indicated that only mongoose predated coqui. Kalij pheasants, chickens, scratching
and overturning leaf litter, may incidentally grab a protein-rich coqui meal. Cats are also reported to prey on
coqui. However, none of these predators take enough frogs to control a population.
Coqui populations in Puerto Rico
are thought to be more affected by predators that include scorpions and snakes. In Puerto Rico, populations of coqui
are much smaller at higher locations (2,500 feet). However, it would be imprudent to extrapolate this trend to
Hawai`i with different vegetation, competing organisms, and predators. The availability of nest and retreat sites
in the understory in Puerto Rico was found to limit coqui populations there. The ginger, tree fern, and uluhe
understory in much of Volcano seem to provide excellent nesting sites and harborage, and ample leaf litter
suitable for invertebrate prey.
Coqui are generalist insectivores which consume a broad range of invertebrates.
Inventories of the stomach contents of coqui were made on Hawai`i Island and Maui in lowland sites with
non-native vegetation and non-native invertebrates. No systematic study of coqui diets has been conducted
Studies from lowland areas with the highest densities of coqui indicate that frog populations
are consuming 285,000 invertebrates/acre/night. Most were leaf litter arthropods
with some herbivorous and flying invertebrates.
Sixty percent of the prey were
non-native ants, amphipods, and isopods. No mosquitoes and a very small percentage of termites
were found in the stomach.
The preference for litter arthropods suggests that Volcano's lush, wet forests
will provide ample food resources for coqui. The lowland diet studies found too that some native
beetles and flies were preyed upon, suggesting the potential for impacts on native invertebrates in higher
elevation native forest. Diet studies do not directly address potential effects on native forest birds,
which largely are found at higher elevations. These birds depend at least partly on caterpillars
and moths with life stages on the ground and available to coqui. It is
also not known if coqui predate arthropods on their nocturnal perches. It is suspected that coqui could
provide an ample prey base for unwanted potential predators such as Brown Tree Snake.
The high densities of coqui and their consumption of huge amounts of leaf litter invertebrates suggests that
coqui could affect litter decomposition and nutrient cycling.
Changes in these ecosystem processes could affect species composition of Volcano forests.
Intuitively, one might expect that leaf litter would accumulate because coqui consume invertebrates that
fragment and decompose litter. However, a recent study in Hawai`i found that plant growth and leaf litter
decomposition rates were actually higher in high density coqui areas than comparable areas without coqui.
Coqui increased leaf litter decomposition rates by producing excrement which provided nutrients to microbes
carrying out decomposition. They increased plant growth by providing nutrients to these plants.
suggest that coqui have the potential to increase nutrient cycling rates. This could give invasive plants a
competitive advantage over native plants which evolved in a nutrient-poor environment.
Coqui are arriving in Volcano as hitchhikers on vehicles, plants, and packaging, probably in that order. Dispersal
to Volcano is increasing as populations densities build up on the island.
Coqui seem to be dispersed to Volcano
primarily on vehicles that are parked in infested areas of the island. Coqui climb on to vehicles in infested areas
to seek harborage or at night to call. When these vehicles slow down or park in Volcano the frogs jump off.
Vehicles delivering goods or services, contractors, family members, or guests are the usual dispersal agents.
There may be more coqui on vehicles that depart infested areas early in the morning while frogs are still perched.
Eliminating all dispersal from vehicles is challenging, especially if you have family and friends driving up to
visit you. There are probably fewer frogs on vehicles that park well away vegetation. It may help to depart
infested area during daylight hours when frogs typically descend from perches to feed on the ground. A visual
inspection of the vehicle may help to some degree, too, but frogs may be tucked away inside wheel wells, bumpers,
and other hard to see or access places.
A thorough washing of vehicles is the most effective means of prevention.
There are very few frogs hitchhiking on rental cars to Volcano's many vacation rentals and B&Bs (except by
employees). Rental cars are washed and inspected. One Volcano Village resident had eight frogs in 2009. She
attributed the coqui arrivals to parking her car at the Hilo airport while working off-island. She now takes her
car to the car wash after leaving the Hilo airport and before driving to Volcano. No frogs were delivered to her
residence in 2010. The car wash at the Chevron station near Walmart also washes the undercarriage for a more
Frogs also frequently arrive on plant material. They may be located on the plants or hiding in the pots or potting
The optimal time to control coqui is when they first arrive in Volcano. They will be calling more consistently then
(even at temperatures below 58 degrees, the temperature below which calling typically ceases) and so are easier to
locate and capture or spray. In addition, a rapid response reduces the chances of successful breeding. The biggest
challenge in controlling coqui in the cooler, more mauka neighborhoods of Volcano is that the frogs will call only
intermittently after the first few days. Once an introduction of coqui frogs develops into a breeding population,
the challenge becomes many times greater and more expensive. Killing hidden egg masses and numerous froglets
requires many repeat applications of citric acid.
Recently some Volcano Golf Course residents brought potted plants to Volcano. They inspected the foliage
before transport and found no frogs or eggs. When they got home, six male frogs, probably hiding in the drain holes
at the bottom of the pots, hopped away but were caught. They uprooted the plants and found many froglets in
cavities within the potting mix. If you have to bring up plants from infested areas, first inspect them, and then
quarantine them in a clear plastic bag or in a closed space for several days.
To sanitize plants, you can soak pots and wash foliage in 113° water (the temperature of a hot shower) for
a few minutes. Check the CTAHR website
for details about the hot shower method of sanitation.
Coqui also hide
in packaging and boxes. You may open up the box for your new water heater from Home Depot and surprise some hiding
coqui. Inspect the outside of the package and open it in a confined space where you can capture frogs if found.
Use a headlamp to keep both hands free. To locate a calling frog, walk 360 degrees around the suspected site.
Some frogs will stop calling if they hear voices or see lights. In this case, it is best to go silent, step back,
and turn off your lights. Imitating the coqui call or playing a recording may elicit a response. Almost all frogs
will go silent if you disturb the vegetation upon which they are perched. If you have to move leaves to locate a
frog, do so very slowly and carefully to prevent your frog from going silent or jumping down.
Frogs high up or
on the ground present a special challenge to locate. You might walk toward a calling frog and you reach that spot
but now the calling seems to be behind you. Then you walk back to the new site and it seems behind you again. This
pattern indicates that the frog is probably high in a tree or tree fern between the two sites or, more rarely, on
Hand capture is probably more effective when two hands are used, one under the leaf or perch and the
other coming down on the frog in a cup-like fashion. In some cases, frogs may be located on the side of a tree fern
or tree so that one hand cannot be placed behind them. Capturing these frogs, even with a cupped hand, is
challenging. You typically have at least 10-30 seconds after spotting a frog to get prepared for capture.
Capture effectiveness is enhanced by working deliberately and with good visibility and access to the prey.
However, one should not wait too long because coqui can jump to lower leaves or to the ground where they are
especially difficult to see.
Coqui frogs are not slimy and are far from fragile. They recover quickly after capture and can jump from your hand
unless firmly held. They should be placed in quart-sized plastic bags -- very carefully because they can easily jump
out of the bag in the process. Flexible bags secured with ties may be safer to use. With zip lock bags, the frog
can be confined to the bottom of the bag with one hand on the outside of the bag, while the top is zipped shut with
the free hand. It's thought that the most humane way to kill captured coqui is to put them in the freezer where they will die,
probably painlessly, within minutes.
Citric acid is ideal for situations in which hand capture is not possible such
as when frogs are located high in tree ferns or trees or deep in uluhe. It is also the best tool when there are
multiple calling frogs and the presence of eggs and females is suspected. Citric acid is the only EPA approved
chemical for use in controlling coqui. Frogs breathe through their skin so they are highly sensitive to chemicals
contacting their skin.
Other products have been reported to be effective such as baking soda, concentrated Simple
Green Soap, and hydrated lime. Caffeine, at about 10 times the concentration found in coffee, was studied for use
but not approved.
Citric acid comes in a granular form and is available from BEI on Kekuanaoa Street and CPS on
Leilani Street in 50 pound bags, at a cost of approximately $100 per bag. Smaller amounts may be available at
Garden Exchange. It is mixed at one pound of acid per one gallon of water and can be applied with a hand sprayer,
back pack sprayer, or larger truck mounted sprayers. Citric acid is effective when it directly contacts the frog
so you need to locate the frog at night on its perch, ideally when it is calling, so that you can confirm its
precise location. Never spray when it is raining. Some applicators spray the ground and understory first, before
the perch site, because frogs may jump from the perches before the spray contacts them. Be thorough when spraying
to ensure contact. With small sprayers, you may need to actually see the frog to make sure the small volume of
spray used actually contacts the frog.
A full 50 gallon drum sprayer used by the Volcano Coquistadores can usually control three separate frogs.
Citric acid can irritate the eyes and openings in the skin. It is prudent to wear eye protection and gloves.
Coqui seek harborage in dark, damp places and you can provide that kind of habitat with ¾ inch PVC pipes
glued together to form a short tee at one end with all three ends left open. Traps are effective about one-third
of the time and are most useful if used in an array in high density coqui areas. Traps should be tied to the tree
or vegetation the frogs are calling from. Consult the CTAHR website for design and placement suggestions.
The effort to control frogs in Volcano is because of the noise they make and because
of potential impacts to native forest and birds.
The optimal strategy for invasive species control is early
detection and rapid response to eradicate newly established populations on the island or in the state. Unfortunately,
coqui are well established and increasing in density on Hawai`i Island and are not eradicable. The strategy in this
case is to prevent their establishment in high value areas such as Volcano community. Frogs are controlled in
higher elevation neighborhoods, even though breeding populations have not been observed there to date. Coqui live
for four to six years, allowing hundreds of noisy frogs to accumulate. With greater numbers the chances of completing
the breeding cycle are enhanced, especially with a warm, wet summer or a warming climate. Other communities on
the island in Kohala, Hāmākua, South Kona,and Ka`ū are also following this strategy. Prevention
and rapid response are the essential components of a strategy of exclusion.
Each neighborhood has a coordinator
who receives reports of frogs, keeps a database, and trains and organizes other volunteers. Ideally, each
neighborhood will develop a cadre of "block captains" who take primary responsibilities for sections
of the neighborhood to share the workload and prevent volunteer burn-out. Control efforts in Volcano focus
on "androcide," killing the calling males, to prevent reproduction. Also, the maturation of egg clutches
may be reduced since males brood the eggs. Females are sometimes captured while searching for males and they are
controlled during spraying operations.
The use of imported biological control agents on coqui is not promising.
Coqui are only minimally susceptible to the chytrid fungus, which is decimating other frog species populations world-wide. The
chytrid fungus is already present in the wild in Hawai`i and Puerto Rico and affects only a very small percentage
of the coqui frogs in both locations.
The greatest contribution you can make is to contact your neighborhood coordinator, receive
on-the-"job" training, and become a "block captain" for residences near your home area.
For example, a block captain in Volcano
Village is the primary person responsible for coqui control on upper Kïlauea Ave, Rohner Lane, and Hāpu`u Lane.
See the latest Volcano Community News for a listing of coordinators and their phone number or call the Volcano Coqui
Hotline (443-4023) for the same information on the recorded message.
Another support role is to report all frogs
you hear to your neighborhood coordinator. They are too busy catching frogs to have time to monitor frogs, and they
may not hear all frogs from the roads and streets in Volcano. A major concern of the Coquistadores is unreported
frogs that may develop into breeding populations. For example, a concerned employee at Kïlauea Lodge reported
a frog deep in the property, beyond hearing range from the roads and driveways. A silent female may eventually find
this calling male and started a population that would finally be heard when it became large enough, but control by
then would have be very difficult.
Another way to help is to donate money for citric acid or other supplies.
Citric acid is expensive and no longer available through state and county grants. Donations can be made at the
coqui frog table at the farmers' market on Sundays, through your neighborhood coordinator, and by check made out
- Cooper Center Council, coqui control
P.O. Box 1000
Volcano, HI 96785