Tropical Nights

Tropical Night in the Illuminated Greenhouses of the Botanic Garden

The Botanic Garden of Johannes Gutenberg University Mainz first participated in the Mainz "Night of the Museums" in 2008, ( converting it into a "tropical night" for visitors in the greenhouses on the JGU campus. At dusk, the Botanic Garden greenhouses, which normally close to visitors at 3:30 p.m., were illuminated at great expense to create a unique atmosphere, and everyone was invited to partake in a somewhat different tour of discovering the plant diversity in the garden. "Thanks to the darkness of the background and the targeted illumination of individual plants, the greenhouse structures seem to merge with the surroundings. The visitors see only the plants and feel as if they are taking an evening stroll through a tropical rainforest," explained the custodian of the Botanic Garden, Dr. Ralf Omlor. To perfect the illusion, night time primeval forest sounds were played.

Visitors were given a tour through five greenhouses. The tour started with the humid tropical greenhouse. Not only do exciting plants live here, such as the cacao tree, but this greenhouse is also home to the nocturnal Caribbean whistling frog (genus Eleutherodactylus). These inconspicuous creatures, only about 2 cm in length, engaged in a mating concert at dusk, the likes of which we only know from songbirds. These shy, small frogs seldom show themselves, but their concert is a really special experience. "This is only the second time we have offered visitors the opportunity to experience the greenhouses and the whistling frogs during the evening and night hours. The first Tropical night was held in July 2003, and was attended by more than 2,000 people," stated Dr. Ralf Omlor. "We deliberately avoided any fringe program to ensure that the tropical plants and the unusual atmosphere in the greenhouses would fully stand out. In the meantime, however, there will always be shorter tours of particular sections on offer." And naturally there was no shortage of tropically inspired drinks and snacks.

For further information please contact
Dr. Ralf Omlor
Botanic Garden of Johannes Gutenberg-University Mainz
Tel.: +49 6131 39 22628

The Caribbean Whistling Frog


The Caribbean Whistling Frog (Eleutherodactylus johnstonei) has already been living in the greenhouses of the Botanic Garden for eight years. "We originally acquired 11 animals from the Botanic Garden of Basle University and released them in the tropical greenhouse. We don't know how many there are today. But they've multiplied significantly in the meantime and are obviously quite comfortable." Since then, they've colonized the other tropical greenhouses at the Botanic Garden. The frogs live under leaves and rocks on the ground, but also in air plants (epiphytes) growing in the upper regions of the greenhouses. During the day, they're dormant and are not usually visible. If the temperature and humidity are high, the male frogs begin their characteristic mating call at dusk made up of two short, differently pitched whistle tones (2000 and 3500 Hz) that they produce one directly after the other at a considerable volume. After a brief pause, the whistling is repeated. Since the males want to vie with one another over the females, a polyphonic whistling concert quickly begins that can last for hours.

Whistling frogs are extremely undemanding. Their original habitat was on Bermuda, but they have since spread throughout the Caribbean. In contrast with our native frogs, they hatch from eggs laid in moist nests in the ground as fully developed little frogs. They do not go through a stage as tadpoles that have to live in water. This is why the whistling frog is able to reproduce so well in a greenhouse environment. After hatching, the little frogs are protected by one of the parents for a short while. The frogs feed on the little insects that live in the greenhouses and therefore do not need additional feeding.