Living up to its usual standards, the BBC’s ‘Planet Earth 2’ series is introducing us to species and wildlife behaviour that is usually only witnessed by a very small number of people. So far this series seems to have created more attention than any previous wildlife documentary. This is thanks, not only to the incredible footage and the unparalleled commentary by Sir David Attenborough, but to the individual species of wildlife which create the drama.
The ‘Islands’ edition contained what is possibly the most talked about sequence in wildlife documentary history – the Galapagos racer snake hunting marine iguanas. In a supporting role, yellow crazy ants were seen causing significant disruption to the red crab migration on Christmas Island. The snake is the subject of a conservation project; the ants one of eradication. Here is a brief introduction to these oblivious stars.
Species: Galapagos racer snake
The Galapagos racer is one of seven species of terrestrial snakes that populate the Galapagos islands. Whilst they were first described in 1860 by Günther, very little is known about their biology and behaviour. According to the Galapagos Conservation Trust, there are four sub-species of the snake, all endemic to the Galapagos. As their territories do not overlap it is likely that the sub-species shown in this episode was the western Galapagos racer as the filming took place on Fernandina where it is found.
The western Galapagos racer is the largest of the sub-species reaching a length of 125 centimetres. As was seen in the footage, they are constrictors and therefore do not rely on venom to kill their prey. Although it seemed like they were hunting in a pack, they actually weren’t, they were all just homing in on the same iguana. They are, in fact, incapable of sharing food as they have no mechanism for tearing the prey apart; therefore, one individual will swallow the prey whole.
Galapagos racer snakes prey on lava lizards, geckos, insects, iguanas, mice, rats and hatchlings of several bird species. They have also been filmed catching fish, a behaviour thought to be unique as no other terrestrial fish has been seen doing so.
All of the species of Galapagos racer snake are under threat and listed as Endangered. The main hazards to their survival are introduced pigs and goats foraging for their eggs and falling prey to the island’s domestic cats.
The Floreana Galapagos Racer snake is currently the subject of a study aimed to determine the population size of the species and to advance the knowledge about their diversity and biology. This sub-species is restricted to the islets of Champion and Gardner off the coast of Floreana Island. Once the study is completed, the aim is to translocate the species to the main Floreana Island.
Species: Yellow crazy ant
Found 2,600km north west of Perth in Australia, Christmas Island is famous for its land crabs. The most iconic of these and the one made famous by numerous wildlife documentaries, is the Red crab. Vast numbers of these crabs migrate to the shoreline to disperse and fertilise eggs each year. But Planet Earth 2 highlighted a significant threat to the crabs – the aptly named crazy ants.
The crazy ant gets its name from its bizarre behaviour when it is disturbed. It moves about erratically in an effort to put off the predator, or human, that caused the disturbance. Their skinny, slightly built body defies their extremely aggressive nature which enables them to displace other species of ants and insects. It is believed they can kill other invertebrates and even small vertebrates by spraying formic acid.
These ants come with a reputation, appearing on the IUCN list of “One Hundred of the World’s Worst Invasive Species”. And for good reason; Yellow crazy ants have the potential to devastate native ‘keystone’ species. Once introduced, they can form super-colonies that may contain 1000s of queens and billions of individuals.
Crazy ants are generalist feeders and whilst being extremely efficient predators, taking a variety of arthropods from the forest floor and canopy, will also eat grains, seeds, decaying matter and vegetation. They also farm sap-sucking scale insects in order to feed on the honeydew they produce. This behaviour is also detrimental to the forest as it gives protection to the scale insects which damage the canopy.
Believed to have originated in West Africa, the ant has managed to increase its range through accidental transportation by road, sea and air, hitching a ride in containers, during the import/export of soil and timber products. Through this method, Yellow crazy ants have populated much of the Indo-Pacific region. On Christmas island, they have so far invaded only about 5% of the rainforest but have had a significant impact on the wildlife with studies showing that about 15 to 20 million crabs have been displaced so far. The island has an on-going control program to suppress the spread of and damage caused by the yellow crazy ant.
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