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The surprising secret of the yellow crazy ant: How does this ant species come to dominate in its new environment?
The crazy ant (Anoplolepis gracilipes), also known as the long-legged ant or the Maldivian ant, is a species of ant native primarily to West Africa or Asia. This ant species has been accidentally introduced to tropical areas around the world and has been given the nickname "crazy" because of its unusual movements. Due to its long legs and antennae, the yellow crazy ant is one of the largest alien ant species in the world.
Characteristics of this species include aggressiveness toward other ants, low aggression toward conspecifics, effective recruitment, and large nests, allowing it to dominate in new environments.
Many introduced ant species, such as the red fire ant and the Argentine ant, are so-called "wandering ants." These characteristics allow the yellow crazy ants to reproduce rapidly in new environments and form super-large colonies, posing a terrible threat to local biodiversity. The International Union for Conservation of Nature (IUCN) lists it as one of the "100 worst invasive species in the world". Its impact range stretches from Hawaii to the Seychelles, and it has formed a super-large colony on Christmas Island in the Indian Ocean.
Physiological characteristics
The yellow crazy ant is a large, yellow to orange ant with long legs, large eyes and extremely long antennae. Although the yellow crazy ant is the only invasive species in the genus Anoplolepis, its appearance can be easily confused with several other genera. Characteristic acid pores and a more compact peduncle help to distinguish them.
Crazy ants are found in high densities on several islands in the Pacific, particularly Christmas Island, which has become one of the most notorious sites of an infestation, causing a collapse in local biodiversity. The strong adaptability of this ant species enables it to gain a foothold in the new environment.
Geographical distribution and diffusion
The yellow crazy ant's natural habitat is primarily the humid tropical lowlands of Southeast Asia, but it has been introduced to areas including northern Australia, several Caribbean islands, and some islands in the Indian and Pacific Oceans. The nests of these ants are highly adaptable, allowing them to be quickly spread to new environments by human transportation.
Crazy ants spread through "ex-nest reproduction," meaning paired females and workers leave the nest to establish new ones, allowing them to expand further even after being transported by humans.
Eating habits
The yellow crazy ant is described as a "scavenger predator". Their diet is broad, including a variety of foods such as grains, seeds, arthropods and meat. Crazy ants rely on plant honeydew as their main source of carbohydrates, which comes primarily from several insects, especially scale insects and aphids.
Studies have shown that crazy ants are highly dependent on scale insects. Once their numbers decrease, their reproduction will be restricted, further affecting their survival rate in newly built nests.
Reproduction Mode
The reproduction pattern of yellow crazy ants is similar to that of other ants, with female ants laying eggs that are fertilized by sperm from male ants. A 2023 scientific article proposed a unique reproductive cycle, noting that male ants have the "must be chimeric" trait, an observation that is the first in the animal kingdom.
This unique reproductive mode may be another important factor that helps the yellow crazy ant gain advantages in new environments, emphasizing its biological adaptability.
Mutualism
The relationship between the yellow crazy ant and its symbiotic scale insects shows its importance in the ecosystem. Ants protect scale insects from predators and help them spread between plants, and the honeydew provided by the scale insects serves as the ants' main food source.
This mutualistic relationship has, to a certain extent, allowed the number of yellow crazy ants to continue to expand, which has had a negative impact on the health of local plants and led to changes in vegetation and biodiversity.
Influence in Australia
In Australia, yellow crazy ants have been found in more than 30 locations, including in Queensland and the Northern Territory. In Queensland, the main ant invasion site covers an area of 830 hectares, with a tropical rainforest background protected as a World Heritage Site, so local control measures for this invasive species are particularly important.
A cost-benefit analysis by the Queensland government pointed out that if the yellow crazy ants are not controlled in time, the potential loss to the Australian economy will exceed A$3 billion.
The impact on Christmas Island
On Christmas Island, yellow crazy ants have had a profound impact on local biodiversity, with the threat mainly reflected in predation on ground crabs and habitat destruction. Studies have shown that ants could kill up to 20 million crabs, which are key species in the ecosystem, responsible for improving soil and growing plants.
These changes triggered a chain reaction in the food chain and caused huge changes in the species structure in the forest, further affecting the local ecological balance.
Control measures
In order to reduce the impact of yellow crazy ants on the Christmas Island ecosystem, Parks Australia launched a large-scale aerial baiting program in 2009 to prevent further declines in crab numbers. After many surveys and mapping, scientists learned the precise locations of large ant colonies and were able to carry out targeted baiting.
While these control measures have temporarily reduced ant populations, the rapid growth and spread of ants makes their control still challenging. Experts call for further strengthening of long-term monitoring and management measures.
So, facing this alien invader, how can humans more effectively protect our ecosystem?
