The green toad is a widely distributed toad species, found from as far west as western Germany to as east as Kazakhstan and western Russia. It is one of the most common and widespread amphibian species in Greece and occurs throughout all of the mainland as well as on several islands. Following a recent study published by Dufresnes et al. (2019), several Asian, European and African populations of the green toad were split into additional species, out of which one, B. sitibundus, was reportedly the second representative of the genus in Greece (east Aegean islands). However, a follow-up study by Dufresnes et al. (2021) confirmed that southeastern European populations should be treated as B. viridis. The same paper also described a new subspecies (B.v.dionysi) from the Cyclades and from Ikaria.
Description
Medium-sized toad, up to approximately 10 cm SVL. The background coloration of the dorsal area ranges from white to salmon orange, with an intermediate greyish/orangeish-cream coloration being the most common. The dorsal area is decorated by irregular (generally) green patches and small red spots (glands), though the brightness and intensity of the colors of the pattern varies immensely. The ventral coloration is greyish white, often with irregular dark grey or olive spots. The skin is tuberculate and dry. The parotoid glands are large, very easily distinguishable and are located behind each eye. The eye is greenish in color and the pupil is horizontal. Sexually dimorphic – females with higher contrast and a more defined, “cleaner” pattern than males, with the dorsal side of males sometimes appearing patternless. Males are smaller and with a more slender build than females. A single vocal sack and nuptial pads are also exclusive to males. Tadpoles small and dark, metamorphs grey with brown spots, but they soon attain a coloration similar to that of the adults.
During the breeding season, males produce a characteristic, continuous high-pitched “trrrrrr” call lasting around ~10 seconds to attract females.
Habitat
Inhabits a vast range of habitats, generally preferring open areas, including but not limited to: maquis shrubland, forest clearings or edges, phrygana, sand dunes, beaches and other coastal habitats, swamps, the riparian zone of streams and even degraded areas such as urban parks, gardens or cultivations. It can be found in very dry habitats miles away from permanent water and it needs no more than a temporary water source to reproduce. Reproduction can occur in any shallow water with little to no aquatic vegetation. These breeding sites can be watering troughs, artificial ponds, wells, watering canals, flooded fields, etc. Up to 2500 m asl.
Riparian zone of a perennial stream – habitat of Bufotes viridis
Cultivated fields and grassland bordering maquis shrubland – habitat of Bufotes viridis
Degraded urban grove next to a stream – habitat of Bufotes viridis
Floodland, breeding site – habitat of Bufotes viridis
Cultivated plain – habitat of Bufotes viridis
Watering trough, breeding site – habitat of Bufotes viridis
Crack retaining water in a severely degraded urban stream, breeding site – habitat of Bufotes viridis
Humid pasture – habitat of Bufotes viridis
Biology
The green toad usually overwinters in burrows, stone walls and other artificial structures, but it can also hibernate underwater in streams or even wells. Southern populations usually do not hibernate and will stay active throughout the year. It is a nocturnal toad that hides underground, under rocks or garbage or in various other refugia during the daytime. It usually avoids becoming active in temperature extremes, i.e. the coldest winter nights and the hottest, driest nights of summer. The ideal conditions for activity seem to be warm, humid or wet nights around 14-18C, especially in late spring or early summer. It can tolerate extreme drought, seemingly more than any other amphibian in Greece. It does not need a permanent body of water to reproduce, and the breeding grounds are very often vernal pools, floodland or drying intermittent streams. It can tolerate significant pollution and it will often reproduce in brackish water. Depending on the location, the breeding season can start from as early as mid-winter and last until as late as early summer, though it is not impossible for calling and reproduction to occur even later in the year. The toads will undertake a migration as long as 5km (though usually shorter) to reach the breeding grounds. Males are virtually always more numerous than females and it’s not impossible to find breeding grounds where the males outnumber the females seemingly as much as 10 to 1. Males very often grasp other males during the courting ritual. Interpretations of this behavior vary, with some hypothesizing it is territorial behavior, and others referring to it as accidental. The males are vigorous and competition for females is fierce, sometimes leading to many individuals wresting over a single female, forming a pile, the weight of which can make the female unable to surface for air and consequently drown. Once a male and female are in amplexus, eggs are laid in long, gelatinous strings and are externally fertilized. The clutch size can vary from 2000-30000 eggs in 2-3 strings. The larvae soon hatch and metamorphosis will take place in the summer, and the time of metamorphosis as well as the size of the metamorph are largely influenced by external factors. For example, tadpoles will metamorphose sooner and at a smaller size in a drying vernal pool and later in the cold water of a perennial stream. The diet of the green toad greatly varies with age, with tadpoles consuming algae, detritus and other organic matter, toadlets mainly preying on microscopic arthropods such as Collembola and Acarina among others and adults most frequently taking crawling terrestrial invertebrates, included but not limited to: Myriapoda, Coleoptera, Isopoda, Annelida, Hymenoptera (including ants). There do not seem to be confirmed records of this species preying on other vertebrates and it is highly unlikely that this occurs. The green toad is not particularly fast-moving and its main defense against predators is its toxin, which is secreted from the parotoid glands as well as the limbs and most of the dorsal area. These toxins render it inedible for most predators, successfully deterring them, but some animals like the grass snake (N. natrix) have become immune to the toxin. The larvae are toxic as well. The toxins are harmless to humans but they will cause mild irritation if they come in contact with the eyes, open wounds or mucous membranes and are potentially dangerous if swallowed. If grasped by the sides, the males will also produce loud croaking sounds and twitch their bodies, which may startle a potential predator.
Distribution
The most widespread amphibian in Greece; occurs in all of the mainland, in the Peloponnese, on Euboea and several other Ionian and Aegean islands, e.g. on Corfu, Kefallonia, Ithaca, Lefkada, Zakynthos, Crete, Kythera, Lesvos, Limnos, Chios, Samos, Skopelos, Thasos, Samothraki and on many of the Cyclades and the Dodecanese islands.
Bufotes viridis dionysi: The green toad populations of Naxos and Ikaria islands have been described as an endemic subspecies (Dufresnes et al., 2021), which is likely to occur on other Aegean islands too.
