The jararaca-ilhoa lives on Queimada Grande Island

The jararaca-ilhoa lives exclusively on Queimada Grande Island, also known as the island of snakes;

The jararaca-ilhoa is a sui generis snake, adapted to arboreal or semi-arboreal life, which is reflected in various aspects of its morphology and behavior.

There are more than 30 cataloged species of jararaca snakes.

Jararaca-ilhoa on the island of Queimada Grande
Jararaca-ilhoa on the island of Queimada Grande

The coastal islands of the southeast coast were formed during the last ice age. They were connected to the mainland around 17,000 years ago, when the sea was 110m below its current level.

With the end of glaciation, the species that remained isolated entered a process of speciation through genetic drift or inbreeding.

As a result, these places have become unique as they are home to endemic species, such as the Bothrops insularis.

Ilha da Queimada Grande

Queimada Grande Island is located about 30 km off the south coast of São Paulo, in the vicinity of Itanhaém and Peruíbe.

ilha da Queimada Grande
ilha da Queimada Grande

Most of its 430,000 m2 is covered by Atlantic forest, but there are grasses in some areas that have been altered by man.

The island of Queimada Grande is mostly above 50m above sea level, with the highest point – Pico da Boa Vista – at 210m above sea level. There are no beaches on the island and the source of fresh water is difficult to access.

The lighthouse still exists today on Queimada Grande Island
The lighthouse still exists today on Queimada Grande Island

In the past, there were residents on the island to keep a maritime lighthouse working, but the current lighthouse is automatic.

The name “Queimada Grande” is not for nothing, since the Navy itself set fire to the island several times for fear of snakes. The practice took place for several 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.

Ilha da Queimada Pequena

The island of Queimada Pequena is also known as the island of Queimada-Pequena, which is also part of the Conservation Unit. The island is much smaller and has no snakes.

Ilhas da Queimada Pequena e Queimada Grande
Ilhas da Queimada Pequena e Queimada Grande

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.

ilha da Queimada Pequena
ilha da Queimada Pequena

Various seabirds frequent the island of Queimada Grande

  • the frigatebird (Fregata magnificens)
  • the gull (Larus dominicanus)
  • the thirty-tailed godwit (genus Sterna)
  • especially the booby (Sula leucogaster), which nests there

In addition to seabirds, around 30 species of birds, most of them migratory, can be seen on the island of Queimada Grande at certain times of the year.

Birds, bats, vertebrates and snakes found on the island of Queimada Grande

There are no land mammals on the island.

  • crocodile (Troglodytes aedon)
  • cambacica (Coereba flaveola)
  • Nyctinomops laticaudatus
  • Nyctinomops macrotis
  • Scinax aff. Perpusillus
  • Eleuterodactylus aff. binotatus
  • Colobodactylus Taunay
  • Hemidactylus mabouia
  • Mabuya macrorhyncha;
Amphisbenids (subterranean reptiles)
  • Amphisbaena hogei
  • Leposternon microcephalum
  • dormouse (Dipsas albifrons)
  • Silver lancehead (Bothrops insularis).

Studies on the lily jararac

The Bothrops insularis was described in 1921 by the herpetologist Afrânio do Amaral (1894-1982), from the Butantan Institute.

In 1959, Belgian zoologist Alphonse R. Hoge (1912-1982) and collaborators, also from the Butantan Institute, reported the presence in several females of the male’s copulatory organ (hemipenis), which was reduced in size, and called them intersex.

It is now known that they are true females and the organ is called a hemiclitoris. These same researchers also collected a hermaphrodite specimen (with both male and female reproductive apparatus) of the lily jararac.

Origin of the lily jararac

On the continent, the species most closely related to the Bothrops insularis is the Bothrops jararaca, which inhabits the Atlantic rainforest.

The two species of snakes are easily distinguished by their coloration pattern, but they also have other differences.

jararaca comum (Bothrops jararaca)
jararaca comum (Bothrops jararaca)

One model to explain the differentiation between the island jararaca and the mainland jararaca is allopatric speciation.

According to this model, two populations separated by some geographical barrier can undergo differentiation over time, becoming distinct species. A scenario of this kind may have given rise to the lily jararac.

The sea level fluctuated during the Quaternary period, creating dry passages between the island and the mainland at various times.

Possibly, at one of these times there was only one ancestral species of jararaca. With the rise in sea level, one population would have remained isolated on the island, differentiating itself into the jararaca-ilhoa, and the remaining population would have originated the mainland species.

Different habits of the jararaca-ilhoa species

The island of Queimada Grande has one of the highest population densities of snakes known in the world.

There are no precise estimates of the total population of lancehead jararacas, but some calculations indicate a figure of between 2,000 and 4,000.

The density of the species on the island is so great that in just one day it is possible to encounter up to 60 of these snakes.

On the mainland, by contrast, studies carried out in the Atlantic rainforest over the last 15 years have found a maximum of three common jararacas per day.

The overpopulation of baby jararacas on the island of Queimada Grande may be due to the near absence of snake predators and the great availability of food.

In several mainland jararaca species, including the common jararaca (Bothrops jararaca), the young individuals have arboreal habits, but the adults are almost exclusively terrestrial.

The adults of the bothrops jararaca are often found on trees and bushes, but they also use the forest floor.

Afrânio do Amaral said that, as well as being more arboreal, the lily jararaca-ilhoa is diurnal and that these two characteristics are related to its diet.

Unlike the majority of jararacas on the continent, whose adults feed mainly on rodents, the diet of adults of the lily jararac is based on birds.

The need for a new diet, since there are no small terrestrial mammals (rodents, marsupials) on the island, has meant that, over the generations, diurnal activity and the arboreal habit have become less advantageous (by favoring the capture of birds) and have been naturally selected for in the population of young jararacas.

Adult female jararacas, however, also capture birds on the ground, and for this they can concentrate under fruit trees, places visited by birds. Lacraias, frogs, tree frogs, lizards and even the other snake that occurs on the island (the dormouse, Dipsas albifrons), seem to be the main prey of the young and, occasionally, the adults.

The birds most preyed upon by the lily jararac are

  • una ibis (Platycichla favipes)
  • tuque (Elaenia mesoleuca)
  • collier (Sporophila caerulescens)

The data published by Amaral and those obtained on recent expeditions to the island indicate that only migratory birds are used as food by the jararaca-ilhoa.

The bird corruíra, a resident and very abundant bird on the island, seems to have learned 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 be the result of food specialization: the action of its venom, which is five times more potent at killing a bird than that of the common jararaca.

The jararaca-ilhoa’s way of dealing with birds is also different from the way the common jararaca deals with rodents.

When it bites a rodent, the common jararaca releases the rodent immediately, as a bite from the animal could seriously injure it.

It then follows the scent trail until it finds its prey, already immobilized by the venom.

The jararaca-ilhoa, 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.

In addition, a bird’s beak and claws don’t pose as great a risk of injury as a mammal’s teeth.

An obvious aspect of the island jararaca’s coloration is the tip of the tail, which is dark in adults and juveniles.

In several species of continental jararacas, the tip of the tail of the young is contrasting (light or dark) with the color of the rest of the body.

If an amphibian or lizard passes 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 jararaca-ilhoa feeds on birds – which also prey on insect larvae – it is possible that it also uses this hunting strategy.

The jararaca-ilhoa appears to mate between March and July, and the young are born in the first few months of the year.

The birth rate seems to be low, as a jararaca-ilhoa litter rarely exceeds 10 offspring, while that of the common jararaca can reach 30.

In addition, few pregnant females were recorded during studies on the island.

Recent expeditions indicate that juveniles are found more frequently at night, a habit that may have been favored by the nocturnal activity of their main prey (amphibians and lacraias).

Thanks to its isolation, today the lancehead jararacara has its own biological characteristics, which differentiate it from other jararacara species.

Alcatrazes jararaca – similar history

Another jararaca – found on the island of Alcatrazes – may have a similar origin.

The Alcatrazes jararaca-de-alcatrazes (Bothrops alcatraz) lives only on Alcatrazes Island, also located 30 km off the coast, but on the north coast of São Paulo.

jararaca-de-alcatrazes (Bothrops alcatraz)
jararaca-de-alcatrazes (Bothrops alcatraz)

As was the case with the Bothrops insularis, this other jararaca is being recognized as a distinct species.

Its origins are probably similar to those of the lynx, but its diet – there are no land mammals on the island of Alcatrazes either – has not turned to birds.

The Alcatrazes jararaca has adapted to eating lacraias 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 young Bothrops jararaca).

Therefore, the bothrops jararaca can be considered a dwarf jararaca, in which some juvenile characteristics have been retained in the adults (a phenomenon called pedogenesis).

Like the jararaca-ilhoa, the jararaca-de-alcatrazes is also at risk of extinction, especially because it occurs on only one island and in low density.

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