GIANT TROPICAL BULLET ANT, PARAPONERA CLAVATA,
NATURAL HISTORY AND CAPTIVE MANAGEMENT

Randy C. Morgan
Associate Curator of Entomology
Insectarium, Cincinnati Zoo and Botanical Garden
3400 Vine Street, Cincinnati, OH 45220 USA
This paper: 1) reviews Paraponera clavata biology relevant to husbandry and educational interpretation, and 2) summarizes Insectarium management techniques stressing keeper and public safety, and environmental needs for colony maintenance and growth.

NATURAL HISTORY

Paraponera clavata is best known for its giant size and unusually severe sting. Workers are 18-25 mm. (up to 1 in.) long and look like stout, reddish-black, wingless wasps. Their stings are the most painful and debilitating known for any insect (Schmidt 1986, 1990).
Taxonomy and Names: The genus Paraponera (Hymenoptera: Formicidae) belongs to the primitive ant subfamily Ponerinae (Bolton 1994) and contains one living species, P. clavata. It has been called the giant tropical ant (McCluskey & Brown 1972, Young & Hermann 1980, etc.) but regionally goes by many colorful names typifying potent sting, such as hormiga bala or bullet ant, and viente-cuatro hora hormiga or 24-hour ant (Weber 1939, Hermann & Blum 1966, Schmidt 1986).

Zoogeography: The Neotropical Paraponera occurs in Atlantic coastal lowland rainforests from Nicaragua southward to and throughout the Amazon River Basin; in Costa Rica it lives at elevations up to about 500 m. (Janzen & Carroll 1983). In Peru, it inhabits both primary and secondary rain forest growth (Morgan pers. obs.), and was the third most abundant ant of 52 canopy-dwelling species found in a small study plot (Tobin 1991).

Social Organization: Paraponera is eusocial though relatively primitive (Wilson 1971). Queens are only slightly larger than workers (thus little modified for egg production), while mature colonies (those producing reproductive forms or winged males and virgin queens) are small and at most contain a few thousand ants (Janzen and Carroll 1983, Breed & Harrison 1988, Morgan 1996). However, workers exhibit a size-based division of labor, with smaller ants tending to remain in the nest as nursemaids and larger workers serving as nest guards and foragers (Breed & Harrison 1988). New colonies are initiated by lone queens and established colonies are monogynous or have a single mated queen (Peters 1993).

Nest Site and Structure: Paraponera nests in the ground at tree bases (Janzen and Carroll 1983, Bennett & Breed 1985, Belk et al. 1989a,b) and sometimes occupies arboreal cavities (Breed & Harrison 1989). Nest sites may be completely shaded or receive varying amounts of direct sunlight (Morgan pers. obs.).
Nests often have a single entrance, but may have multiple openings (Hermann 1975, Young & Hermann 1980). Main entrances typically abut tree trunks or plant bases (Belk et al. 1989a,b). Secondary openings may be used for soil removal (Young & Hermann 1980). A large nest had tunnels leading from the entrance downward and outward to 43 chambers 7-62 cm. below ground (Janzen and Carroll 1983). Nest chambers were 5-10 cm. in diameter, flat floored with slightly domed ceilings 13-16 mm. high, and sometimes closely stacked in tiers. Breed and Harrison (1988) noted that drainage or escape tunnels extend below the deepest chamber.


Foraging and Food: Workers forage in the canopy and understory (Jansen & Caroll 1983, Bennett & Breed 1985, Harrison & Breed 1987, Belk et al. 1989) and less often on the ground (Young & Hermann 1980, Breed & Bennett 1985). Nest-associated trees are used to reach the canopy (Belk et al. 1989a,b). Nestmates are recruited via pheromone trails (Barrett et al. 1985, Breed & Bennett 1985, Breed et al. 1987, Fewell et al. 1992) and experienced foragers also rely on landmarks (Harrison et al. 1989). Peak foraging is often crepuscular and nocturnal (McCluskey & Brown 1972, Hermann 1975) though significant foraging can occur diurnally and is weather-influenced (Young & Hermann 1980).
Paraponera is a generalized predator-scavenger and collects liquid droplets, prey, and plant parts (Young & Hermann 1980). Extra-floral nectar is a principal dietary component (Hermann 1975, Breed & Bennett 1985, Fewell et al. 1992). Liquid sucrose is strongly preferred over honey-water (Morgan 1996). Water is also collected; both nectar and water are shared with nest ants, or placed as tiny droplets on feeding larvae (Morgan pers. obs.).

Solid food items are mostly arthropods, other invertebrates, and occasionally pieces of small vertebrates (Young & Hermann 1980, Morgan 1996). Foragers are strongly attracted to termites (Barrett et al. 1985, Morgan 1996). Small food items are carried whole, while larger ones are first cut apart, then shared with nest ants, or placed on or next to feeding larvae (Fig. 1). Plant pieces are used to frame spinning larvae, for pupal bedding and, along with empty cocoons, to line nest chamber walls (Morgan pers. obs.).

Enemies and Mimics: Paraponera's natural enemies include conspecifics from other colonies (Hermann & Young 1980, Breed et al. 1991), parasitoid Phorid flies (Janzen & Carroll 1983, Brown & Feener 1991, Feener et al. 1996), and an entomopathic fungus that characteristically leaves mummified spore-bearing ants clinging to vegetation (Morgan pers. obs.). A cerambycid beetle mimics Paraponera (Silberglied & Aiello 1976).

Stings, Venom, and Defensive Behavior: Ponerine ants typically have large well-developed stings and abdominal stridulatory (sound producing) organs (Bolton 1994). Paraponera sting apparatus was detailed by Hermann & Blum (1966), Hermann & Douglas (1976) and Hermann et al. (1984). The sting is used offensively during food foraging and defensively for protection (Herman & Blum 1966). The venom is neurotoxic (Schmidt 1986), blocks insect central nervous system transmission, and is agonistic to mammalian smooth muscle (Piek et al. 1991). Paraponera is not aggressive except when defending self or territory. When their nest is disturbed, defenders swarm out, release a heavy musky odor, stridulate an audible warning (Janzen & Carroll 1983), then grab and impale intruders.

Human Sting Reactions: Sting victims' reactions have been described by Bequaert (1926), Weber (1937, 1939), McCluskey & Brown (1972), Schmidt (1990) and Morgan (1996). Intense pain typically lasts 3-5 hours then lessens over the next day. Severe pain may be accompanied by trembling, perspiration, nausea, and inability to use an injured arm or leg. Some South American Indians intentionally applied stings during tribal manhood rituals (Bequaert 1926) and medicinally to treat rheumatism and similar ailments (Weber 1937).

CAPTIVE MANAGEMENT
An effort by McCluskey and Brown (1972) to collect and culture Paraponera for behavioral research was largely unsuccessful. Beginning in 1992, the Insectarium made several attempts to excavate and rear live colonies for display (Morgan 1996). Though initial results were variable, experimentation and technique refinement yielded effective management procedures. We emphasize keeper and public safety while meeting bullet ant colony needs.
Two queen-right colonies have thrived and proliferated for nearly two years.
A field-caught 500+ ant group, on public display since July 1996, has grown to over 1,200 workers and is producing males and virgin queens. A back-up laboratory colony, started by combining a newly mated queen with a few young workers, contains about 200 ants and is growing.

Keeper Safety Guidelines: All caging and service access portals are conspicuously labeled "HOT" and "VENOMOUS", calling attention to the presence of potentially dangerous animals. Servicing is limited to a few competent employees who feel comfortable working with these ants. Keepers are trained to: 1) inspect and monitor service portal perimeters before opening and while inserting their arms, 2) avoid making jarring vibrations or exhaling directly on the ants, both tending to stimulate alarm behavior, 3) always use long (30 cm.) forceps to change food dishes or remove debris, and 4) employ a spotter for safety during disruptive procedures, such as major cleanings or nest manipulations.

Sting Treatment and Medical Considerations: Individual sting treatment procedures for bullet ant keepers were developed in consultation with their personal physicians. For example, my protocol is to immediately immerse the sting site in an ice-water bath to slow venom spread, and to ingest a maximum dose of Benedryl* (antihistamine) capsules to counter possible allergic response. This combination effectively mitigates pain and induces drowsiness, encouraging relaxation or sleep during the worst part of the venom's reaction. In the event of a severe systemic reaction, such as difficulty breathing or swallowing, I have several EpiPens* (self-injectable epinephrine), a Proventil* (asthmatic) inhaler, and Prednisone (steroid) tablets, all physician-prescribed.

Generalized employee response and care guidelines were also adopted. Sting victims are expected to stop work, relax, be closely monitored by the Zoo's paramedic or another employee, and be transported to a local hospital emergency room if requested or at the first sign of distress. The emergency room's telephone number is conspicuously posted so hospital staff can be quickly notified that a sting victim is en route.

Caging and Containment: For employee and visitor safety, all caging components fit securely and are constructed to resist accidental or intentional damage. Basic building materials like plate glass, heavy wire screen and plywood are ant damage-proof, since the workers' mandibles are not particularly sharp or powerful.

For laboratory caging, we use standard 150 liter (40 gal.) glass aquaria to contain ant nest chambers and feeding stations. Small colonies (<200 ants) are housed in a single tank, while large groups are kept in two interconnected tanks. The latter arrangement allows us to concentrate most of the ants in one tank, used for nesting, in turn facilitating safer routine servicing in the other less populated tank, used for feeding and foraging.

Tank top covers contain service portals and ventilation holes. Service portals and perimeter areas are constructed from clear or light-colored materials to enhance ant detection. Overhead portals can be opened with few escape attempts if nest chambers are placed near tank bottoms and ant runways are positioned to encourage foraging away from access sites. Several ventilation holes in each top cover end are screened with 8 mesh/2.5 cm. galvanized metal hardware cloth. These allow air exchange and cross ventilation, and help limit condensation on inner viewing surfaces caused by external temperature fluctuations.

Nesting Chambers: In captivity, Paraponera is an opportunistic nester and will occupy almost any available sheltered cavity when needing space. Most of our populous display colony lives in a large Hydrostone (US Gypsum* cement) block containing pre-cast tunnels and nest chambers. However, part of the colony resides in an adjacent, horizontally-tiered wooden box. Both nests are glass fronted for colony observation.
Our laboratory colony is housed in six 17x12x6.5 cm. clear plastic boxes with tightly fitting lids. Each box has a 2-3 cm. thick Hydrostone floor providing an absorbent base layer, and is drilled with a single 1.5 cm. diameter entrance hole at ground level. These nest chambers are modular (independently movable) and not interconnected with tunnels. Worker ants, sometimes carrying brood, travel openly between boxes. Additional boxes will be added as the colony grows.

Nest Temperature and Lighting: Nest chambers are exposed to a temperature gradient (22-27 ºC.), allowing the ants to choose their thermal optimums for brood rearing. Pupae and occasionally large larvae are incubated in the warmest sites. Colonies grow normally, but perhaps more slowly, under relatively uniform conditions (22-23 ºC.). Spot heating effects are created with incandescent lights and monitored with a thermometer. Moderate illumination levels do not seem to disrupt normal behaviors and further enhance colony viewing.
Food and Water: The ants are provided fresh nectar and prey every 1-2 days, while clean distilled water is continuously available. Food quantities offered depend on colony population and recent consumption rates. For example, a typical daily feeding for our 1,200+ ant display colony is 40-50 ml. of nectar and 1-2 dozen large to medium-sized insects. Prey items are scattered on foraging tank floors and liquids held in small shallow dishes placed on elevated, easy-to-reach platforms for safer servicing.
Nectar: Keepers prepare a liquid formula as follows: 300 ml. distilled water, 4 rounded tbsp.(50-60 gr.) granulated table sugar (sucrose), and a small pinch (about 0.05 gr. each) of Vanderzant Vitamin Mix and Wesson Salt Mix (ICN Biomedicals). This produces about a week's supply, with the unused portion refrigerated until needed.
Prey: Food diversification seems important since the ants tend to lose interest in prey items provided several days in a row. We use surplus insects from Insectarium rearing programs supplemented with locally caught termites. Standard food items include various termite spp. (Isoptera), roach spp. (Dictyoptera), cricket and katydid spp. (Orthoptera), walking stick spp. (Phasmatoptera), meal worms and adults (Coleoptera), wax worms (Lepidoptera), and bottle flies (Diptera). Large or active prey (i.e., grasshoppers, roaches, flies) are first killed by freezing and stored frozen until needed. Live termites and mealworms are sometimes confined in a small bowl provided with ant access ramps.

Garbage and Cleaning: Colony garbage consists of uneaten prey, empty cocoons and dead ants. Workers tend to pile waste and defecate in tank corners away from the nest, probably preferring more distant dump sites. Everyfew days, old prey and larger garbage items are picked out with forceps. Weekly, a small shop vacuum cleaner is used to remove accumulated fine debris. Ant fecal droplets on viewing glass are wiped clean with damp paper towels or, in less accessible areas, safely scraped away using a straight-edged razor blade mounted on the end of a stick.

Ant and Colony Manipulations: Captive management sometimes requires individual ant or group manipulations. Ants are firmly grasped with forceps, moved and released without harm, since they are thick cuticled. They can also be encouraged to retreat from specific areas by spraying them with a hand-held water mister.

Ants can be temporarily immobilized by two equally effective methods. Chilling causes ants to become torpid, and can be done gradually by refrigeration or rapidly by dropping them into in a dry jar immersed in ice water. When warmed they resume activity. Alternately, brief exposure to concentrated carbon-dioxide gas quickly induces narcosis. Since this gas is heavier than air, follow-up ventilation is critical for recovery and to avoid overexposure and death.

Modular nest chambers facilitate colony-level manipulations. After nest entrance holes are securely plugged, the confined ants can be moved en masse to a new location, either temporarily or permanently, and subsequently re-released.
Public Display and Safety: Our exhibit consists of two, 227 liter (60 gal.) tanks built with 9 mm. thick glass and fitted with double-locked lids. One tank contains a naturalistic observation nest, the other tree stumps used for feeding platforms, and both are decorated with silk plants and vines. A long clear unbreakable Lexan (polycarbonate plastic) tube serves as an interconnecting ant runway. The display is unlocked, opened and serviced before public hours, and monitored by the Insectarium's Security Guard.
We popularize Paraponera as "Bullet Ants -The World's Most Venomous Insects". Graphic artwork identifies colony members and brood stages, and interpretive text explains social organization, foraging and defensive behavior. The ants' giant size, notoriety, and constant activity make them intriguing live display subjects. Media and public response continues to be phenomenal, and the exhibit reigns as one of our most popular insect displays.

Acknowledgments: This work was made possible with assistance from the Cincinnati Zoo & Botanical Garden, International Expeditions, Explorama Tours, the Amazon Center for Environmental Education and Research (ACEER) Foundation, Office of the Ohio Secretary of State, Consulate of Peru, Forestal y Fauna Silvestre-Peru National Institute of Natural Resources, Ohio and U.S. Departments of Agriculture, and U.S. Fish & Wildlife Service. Donald Hawley MD provided medical consultation. Milan Busching, Karen Schmidt & Theresa Austing assisted husbandry. Cincinnati Zoo Volunteers' Organization funded the exhibit in memory of devoted volunteer Sue Peirce. Joanna Wright and Dave Bechtol aided exhibit design, Milan Busching and Ben Horten helped construction, and Joyce Turner created artwork. Kathy Beil-Morgan offered useful manuscript comments.


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