Impact On Christmas Island
The crazy ant has a significant destructive impact on the island's ecosystem, killing and displacing crabs on the forest floor. The super-colonies also devastate crab numbers migrating to the coast. This has seen a rapid depletion of land crab numbers which are vital to Christmas Island's biodiversity. They are a keystone species in the forest ecology by digging burrows, turning over the soil, and fertilising it with their droppings. Seedlings that were previously eaten by crabs started to grow, and as a result, changed the structure of the forest. Weeds also spread into the rainforest because there are no crabs to control them. One of the most noticeable changes in the forest is the increased numbers of stinging tree Dendrocnide peltata, which now flourish along many of the walking tracks and other areas that people frequently visit around the island. Robber crabs, red crabs, and blue crabs are completely wiped out from infested areas. Populations of other ground and canopy dwelling animals, such as reptiles and other leaf litter fauna have also decreased. During crab migrations many crabs move through areas infested with ants and are killed. Studies show the ant has displaced an estimated 15-20 million crabs by occupying their burrows, killing and eating resident crabs, and using their burrows as nest sites. Although crazy ants do not bite or sting, they spray formic acid as a defence mechanism and to subdue their prey. In areas of high ant density, the movement of a land crab disturbs the ants and as a result the ants instinctively spray formic acid as a form of defence. The high levels of formic acid at ground level eventually overwhelms the crabs, and they are usually blinded then eventually killed. As the dead crabs decay, a bonus source of protein becomes available to the ants. Ants in general require two main types of food: carbohydrate to provide energy for the foraging workers, and protein to enable the queens to produce eggs. Crazy ants get much of their food requirements from scale insects. Scale insects are serious plant pests that feed on sap of trees and release honeydew, a sugary liquid. Ants eat honeydew, and in return protect the scale from their enemies and spread them among trees. This relationship is called a mutualism. The honeydew not eaten by ants drips onto the trees and encourages the growth of sooty mould over the leaves and stems giving the plants an ugly, black appearance, and reducing the health and vigour of the plant. In summary, crazy ants kill the fauna, but encourage scale insects. Increased densities of scale insects causes forests trees to dieback, creating light gaps in the forest canopy. Light gaps and removal of crabs encourages seedling growth and weed invasion into the forest.
Read more about this topic: Yellow Crazy Ant
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