Yellow Crazy Ant Queen connecting with a Human

SUB FAMILY / GENUS

Anoplolepis gracilipes formerly known as Formica longipes, is an ant species belonging to the Formicinae sub-family and the Anoplolepis genus.

From Latin, anoplolepis - anopl + lepis (with no scales) and gracilipes - gracilis + pes (thin + legs or feet).

Yellow Crazy Ant Worker carrying a pupae

The genus Anoplolepis consists of a total of 9 species, plus 5 subspecies, all of which are originally from Africa, with the exception of the Anoplolepis gracilipes which is the sole member of the genus to extend its range outside this area.

DISTRIBUTION

There is much disagreement on the origin of this species, which was first described by Jerdon in 1851 in India.

Since then, several authors have described A.gracilipes as native to some or most parts of tropical Asia, which is supported by some evidence such as symbionts from Asia and others.

Anoplolepis gracilipes worldwide distribution

Others considered Africa as the origin of this species since the genus Anoplolepis is known to be almost exclusively African, as we said before.

A striking aspect of A. gracilipes distribution is how the earliest ant surveys found it already widespread over southeast Asia and islands of the tropical Pacific and Indian Ocean. By 1895, when the world’s ant fauna was still very poorly known, A. gracilipes was already recorded from virtually the full range of its current known distribution

COMMON NAME

Anoplolepis gracilipes is commonly known by one of two names, the first and most common is the Yellow Crazy Ant and second but more scientifically correct is the Slender Leg Ant. The name crazy ant arises from its characteristic behaviour that is to run erratically in rapid movements when disturbed, and the name slender leg comes from their long and thin stalky legs.

Yellow Crazy Ant Workers gathering their pupae into a pile

MORPHOLOGY

Anoplolepis gracilipes total body length is around 4mm, but when accounting for its legs length, that length can easily triple. As such it is considered as a medium sized, with a long slender gracile body, with long legs, large eyes, extremely long antennae and a yellow to orange coloration. Workers are monomorphic, displaying no physical differentiation.

Anoplolepis gracilipes Queen and Worker communicating

FORAGING & RECRUITMENT

The activity rhythm of ants is controlled by both endogenous and exogenous factors.

An exogenous rhythm is a rhythm of activity which is a direct response to environmental cues such as temperature and cycles of light, while an endogenous rhythm is a self-sustained cycle of activity.

Anoplolepis gracilipes forages continuously across the ground and in the canopy and is positively correlated with ambient relative humidity and negatively correlated with ambient temperature. This means the ants love high humidity but high temperatures not so much.

Ants can be categorized into nocturnal, diurnal and crepuscular species according to their circadian rhythm of foraging activity. A. gracilipes could be considered a nocturnal or crepuscular species as they forage more intensively at night and early morning.

Yellow Crazy Ant foraging in the flowers at night

Activity on the surface of the ground was observed between 6:00 and 9:30 h and between 16:30 to 23:30 h. During the middle of the day, no ants were observed until the leaf litter was disturbed when large numbers emerged from under leaves and out of rotten logs.

FOOD PREFERENCES

Food is discovered rapidly, even more rapidly and in lower numbers than Paratrechina longicornis.

Described as a “scavenging predator”, it preys on a variety of litter and canopy fauna, from small isopods, myriapods, molluscs, arachnids, and insects to large land crabs, birds, mammals, and reptiles.

Yellow Crazy Ant colony preying on an unfortunate beetle

Just like Oecophylla and BCA, YCA workers subdue their prey down by a method known as spread-eagle, where workers pull the prey’s appendages in different directions, while spraying them with formic acid.

In addition to these protein-rich foods, A. gracilipes obtains carbohydrates and amino acids from plant nectaries and especially from honeydew excreted by Homoptera, which it tends on stems and leaves of a wide variety of tree and shrub species.

A factor that may promote the success of invasive ants is their ability to exploit these carbohydrate resources.

It has been considered that these carbohydrate-rich resources promote ant invasions by providing high-energy fuel for greater activity, growth and the establishment of dominant supercolonies, as well as drive the aggressive behaviors of some invading ant species.

Anoplolepis will generally only demonstrate aggression towards other ants when defending resources, other than that, they normally only display evasive or indifferent behaviour when individuals or groups are confronted.

Yellow Crazy Ant worker drinking sugary liquids

But when involved in a battle with another ant species, A. gracilipes will curve its abdomen up toward the head of its attacker and spray a defensive substance from poison glands located in the abdomen. This secretion is highly toxic to other ants as well as to other individuals within the colony and is a very effective defence.

This is one of the reasons why when capturing wild colonies, one should use an open container, instead of a closed one, since the queens and workers could well suffocate on their own defensive acid.

NESTING PREFERENCES

Anoplolepis gracilipes is primarily a species of the lowland, tropical rainforest, preferring moist forests or other humid habitats and it is capable of invading both disturbed and undisturbed habitats.

Yellow Crazy Ant colony nesting inside a crevice between two man made structures

Nesting requirements are generalized; they nest under leaf litter, in cracks and crevices in the soil, usurp land crab burrows, readily colonize bamboo sections when placed on the forest floor, and in canopy tree hollows. They also nest under the ground substrate, in urban structures, and even in human materials.

LIFE / REPRODUCTION CYCLE

At 26C or 79 F and 70% RH, the brood life cycle is as follows:

The egg stage lasts between 12 and 15 days

The larval stage lasts between 7 and 10 days

The pupal stage lasts between 11 and 15 days

Thus, the complete developmental duration of A.gracilipes is between 30 and 40 days.

At lower temperatures 20 to 22 C or 68 to 72F, the brood cycle is extended to 54 to 60 days

Workers live for approximately 6 months, and the queens for several years.

Alates can be present year-round, but in most instances, initiation of brood follows the beginning of the wet season.

REPRODUCTIVE STRATEGY

As in the other invasive ants, A. gracilipes normally practices a polygynous–polydomous social structure, and a new colony is normally established by dependent colony foundation; that is, queen(s) leave their mother nest for a new nest site with workers, which is also called budding.

Nonetheless, alate queens can fly, and queens and males have been collected by light traps, but dispersal by flight and independent colony foundation seldom occurs.

No reports on solitary queens or incipient colonies with nanitic workers of A.gracilipes have been published until July 2016, when four solitary queens with some eggs under stones were found and collected in a Botanical Garden, in East Java, Indonesia.

The queens were kept individually in artificial nests.

These nests were put in an incubator with constant temperature (26°C) and were not provided any prey or water for keeping the condition of claustral colony foundation. After 40 days, the workers reared claustrally by the queens were nanitic, having a head width significantly smaller than those of a mature colony.

Solitary founding queens or founding colonies with nanitic workers as produced in the laboratory have never been found for this species in research on ants for the last 25 years at several places in Southeast Asia.

In ants, independent colony foundation is an ancestral trait for species with alate queens, and so it is thought that the areas where A. gracilipes commonly found a colony independently may be its native localities.

The findings show that A. gracilipes practices both independent and dependent colony foundation, which is a fantastic discovery for this species.

But the new discoveries don’t end here! You won’t believe what scientists found next!

They found that A. gracilipes workers are not sterile, and are able to produce both trophic and reproductive eggs.

Reproductive eggs developed only into haploid males.

And those trophic eggs appear to be the main food source for larvae in A. gracilipes colonies.

But the most significant dispersal method is none of the above, it is the human-mediated dispersal, where colonies are inadvertently transported to new locations by humans, for example, in potted plants, containers, or rubbish.

TRAMP SPECIES

In recent years, globalization of trade has accelerated the rate of biological invasions and led to disturbances and destruction of native ecosystems around the world.

Yellow Crazy Ant Queen alate ready for its nuptial flight

Social insects, especially ants, are regarded as one of the most devastating groups of invaders because ants have important roles in various ecosystems as keystone species.

The Yellow Crazy Ant Anoplolepis gracilipes is ranked as among the top 100 of the ‘World’s Worst Invaders and is considered one of the world’s most wide-spread, ecologically and economically damaging invasive ant species, and like many other invasive ant species it can reach extraordinarily high population densities and substantially modify ecosystems.

In contrast to the majority of ant species, A. gracilipes supercolonies are characterized by a combination of traits (polygyny, in nest mating and budding) that ensure the continuous production of generation upon generation of reproductives that all stay within the supercolony.

In favourable conditions A. gracilipes can attain very incredible numbers

High densities: 10 million/ha.

Nest size averages about 4000 individuals

Reported rates of spread of between 0.1 and 1.1 m/day

But some populations of A. gracilipes were found to decline or disappear, which may be good news to the local ecosystems.

Invasive species are thought to be vulnerable to several factors that may lead to population declines such as

● Low genetic diversity resulting in inbreeding

● Migration

● Overexploitation of resources

● Pathogens

Unexplained population declines such as these represent an unique opportunity to investigators.

Identifying the drivers and mechanisms behind such declines could have important applications for invasive species management worldwide. And this type of population decline seems to be happening regularly all over the world with many different invasive species, not just only ants.

Cannot wait for more results on this topic!!

CONCLUSION

Hope you have enjoyed reading this post and I have left you a very small video in the link down below with, in case you are interested, about the super invasive characteristics of these ants.

Yellow Crazy Ants - Invasive Ant Super Colonies

Yellow Crazy Ants - Care Guide and Ecology