The jararaca-ilhoa lives exclusively on the island of Queimada Grande, also known as the island of snakes.
The jararaca-ilhoa is a sui generis snake, adapted to living in trees or semi-trees, which is reflected in various aspects of its morphology and behaviour.
More than 30 species of jararaca snakes have been catalogued.
The coastal islands of the south-east coast were formed during the last Ice Age. They were connected to the mainland about 17,000 years ago, when the sea was 110 metres below its present level.
With the end of the glaciation, the species that remained isolated began a process of speciation through genetic drift or inbreeding.
As a result, these places have become unique, hosting endemic species such as Bothrops insularis.
Queimada Grande Island
Queimada Grande Island is located about 30 kilometres off the south coast of São Paulo, near Itanhaém and Peruíbe.
Most of its 430,000 m2 are covered by Atlantic forest, but there are grasslands in some areas that have been altered by man.
Most of Queimada Grande is over 50 metres above sea level, with the highest point – Pico da Boa Vista – at 210 metres. There are no beaches on the island and the source of fresh water is difficult to access.
In the past, the island’s inhabitants were responsible for maintaining a lighthouse to signal the arrival of ships, but the current lighthouse is automatic.
The name “Queimada Grande” is no coincidence, as the navy itself set fire to the island several times for fear of snakes. The practice went on for centuries in an attempt to put an end to the excessive snake population. The fires were large and could often be seen from the mainland.
Queimada Pequena Island
Queimada Pequena Island, also known as Queimada-Pequena Island, is also part of the reserve. The island is much smaller and has no snakes.
The island is almost pure rock with a remnant of Atlantic forest on top. The island has beautiful cliffs and flocks of thirty-réis resting.
Several seabirds frequent the island of Queimada Grande
- Frigate Bird (Fregata magnificens)
- Common Gull (Larus dominicanus)
- the thirty-tailed godwit (genus Sterna)
- and, above all, the atobá (Sula leucogaster), which nests there.
In addition to seabirds, around 30 species of birds, most of them migratory, can be seen on Queimada Grande Island at certain times of the year.
Birds, bats, vertebrates and snakes found on Queimada Grande Island
There are no land mammals on the island.
Birds
- Corruyra (Troglodytes aedon)
- Cambacica (Coereba flaveola)
Bats
- Nyctinomops laticaudatus
- Nyctinomops macrotis
Amphibians
- Scinax aff. Perpusillus
- Eleuterodactylus aff. binotatus
Lizards
- Colobodactylus Taunay
- Hemidactylus mabouia
- Mabuya macrorhyncha;
Amphisbaena (Subterranean Reptiles)
- Amphisbaena hogei
- Leposternon microcephalum
Snakes
- Dormouse (Dipsas albifrons)
- Bothrops insularis.
Studies on bothrops insularis
Bothrops insularis was described in 1921 by the herpetologist Afrânio do Amaral (1894-1982) of the Butantan Institute.
In 1959, the Belgian zoologist Alphonse R. Hoge (1912-1982) and his collaborators, also from the Butantan Institute, reported the presence of the male’s reduced copulatory organ (hemipenis) in some females and called them intersex.
It is now known that they are true females and the organ is called the hemiclitoris. The same researchers also collected a hermaphrodite specimen (with both male and female reproductive organs) of the jararaca-ilhoa.
Origin of the jararaca-ilhoa
On the continent, the species most closely related to Bothrops insularis is Bothrops jararaca, which lives in the Atlantic rainforest.
The two species are easily distinguished by their colour patterns, but there are other differences as well.
One model to explain the differentiation between the common jararaca and the mainland jararaca is allopatric speciation.
According to this model, two populations separated by a geographical barrier can differentiate over time and become separate species. Such a scenario could have given rise to the Jararac lily.
During the Quaternary period, sea levels fluctuated, creating dry passages between the island and the mainland at various times.
It is possible that at one of these times there was only one ancestral species of jararaca. As sea levels rose, one population would have remained isolated on the island, differentiating into the jararaca-ilhoa, and the remaining population would have given rise to the mainland species.
Different habits of the jararaca-ilhoa species
The island of Queimada Grande has one of the highest known densities of snakes in the world.
There are no precise estimates of the total population of the giant lancehead snake, but some calculations put the number between 2,000 and 4,000.
The density of the species on the island is such that it is possible to see up to 60 of these snakes in a single day.
On the mainland, however, studies carried out in the Atlantic Forest over the last 15 years have found a maximum of three common jararacas per day.
The overpopulation of baby jararacas on Queimada Grande Island may be due to the near absence of snake predators and the abundance of food.
In several mainland jararaca species, including the common jararaca (Bothrops jararaca), juveniles are arboreal, but adults are almost exclusively terrestrial.
Adults of Bothrops jararaca are often found in trees and bushes, but they also use the forest floor.
Afrânio do Amaral says that the jararaca-ilhoa is not only more arboreal, but also diurnal, and that these two characteristics are related to its diet.
Unlike most jararacas on the continent, whose adults feed mainly on rodents, the lily jararaca-ilhoa’s diet is based on birds.
The need for a new diet in the absence of small terrestrial mammals (rodents, marsupials) on the island has meant that, over the generations, diurnal activity and arboreal habits have become less advantageous (favouring the capture of birds) and have been naturally selected for in the population of young jararacas.
However, adult female jararacas also prey on birds on the ground, and to do this they can concentrate under fruit trees, places visited by birds. Lacraias, frogs, tree frogs, lizards and even the other snake found on the island (the dormouse, Dipsas albifrons) seem to be the main prey of juveniles and occasionally adults.
The birds most preyed upon by the Lily Jarac are
- Common Thrush (Platycichla favipes)
- Tuque (Elaenia mesoleuca)
- Little Crested Bird (Sporophila caerulescens)
The data published by Amaral and those obtained during recent expeditions to the island indicate that only migratory birds are used as food by the jararac.
The corruíra, a resident and very abundant bird on the island, seems to have learnt to avoid the snake’s attack, according to our preliminary observations.
In addition to the partial shift from the ground to the trees, another characteristic of the jararaca-ilhoa seems to stem from its dietary specialisation: the effect of its venom, which is five times more potent in killing a bird than that of the common jararaca.
The way the jararaca-ilhoa deals with birds also differs from the way the common jararaca deals with rodents.
When bitten by a rodent, the jararaca-ilhoa will immediately release the rodent, as a bite from the animal could seriously injure the jararaca-ilhoa.
It then follows the scent until it finds its prey, which is already immobilised by the venom.
The Lily Jararac, on the other hand, holds the captured bird in its mouth until the poison kills it. If released, the bird would fly away until the poison took effect, leaving no scent trail on the ground.
What’s more, a bird’s beak and claws are less likely to cause injury than a mammal’s teeth.
An obvious aspect of the island jaraca’s colouration is the tail tip, which is dark in adults and juveniles.
In several species of continental jararaca, the tip of the tail of juveniles contrasts (light or dark) with the colour of the rest of the body.
When an amphibian or lizard comes close to a young snake in search of food, it imitates the movements of an insect larva with the tip of its tail. The ‘false larva’ attracts the prey and makes it easier to catch.
As the Lily Jararac feeds on birds – which also prey on insect larvae – it is possible that it also uses this hunting strategy.
The Lily Jararac appears to mate between March and July and the young are born in the early months of the year.
The birth rate appears to be low, as a jararaca-ilhoa litter rarely exceeds 10 young, while that of the common jararaca can reach 30.
In addition, studies on the island have found few pregnant females.
Recent expeditions indicate that juveniles are more likely to be found at night, a habit that must have been favoured by the nocturnal activity of its main prey (amphibians and lacraias).
Thanks to its isolation, the lancehead jararaca-ilhoa now has its own biological characteristics, which distinguish it from other jararaca species.
Jararaca-de-alcatrazes – a similar story
Another jararaca – found on Alcatrazes Island – may have a similar origin.
The Alcatrazes jararaca-de-alcatrazes (Bothrops alcatraz) lives only on Alcatrazes Island, also 30 kilometres off the coast, but on the north coast of São Paulo.
Like Bothrops insularis, this other jararaca is recognised as a separate species.
Its origin is probably similar to that of theilhoa jararaca-, but its diet – there are no land mammals on Alcatrazes Island – has not changed to include birds.
The Alcatrazes jararaca has adapted to eating snakes and lizards, like the young of the mainland jararaca.
This adaptation included a reduction in the size of this snake and changes in its venom (also similar to that of the juvenile Bothrops jararaca).
The Alcatrazes jararaca-de-alcatrazes can therefore be considered as a dwarf jararaca-de-alcatrazes in which some juvenile characteristics have been retained in the adult (a phenomenon called pedogenesis).
Like the lily-of-the-valley, the Alcatrazes lizard is in danger of extinction, especially as it is found only on one island and in small numbers.
