Step aside, fire ants, there’s a new, big-headed, six-legged female sheriff in town

Photograph by R.H. Scheffrahn, University of Florida

I woke up and read two interesting news articles.

The articles noted that "bigheaded ants", which presumably are Pheidole megacephala, have slowly been taking over south florida and pushing aside the usual fire ants (Solenopsis invicta).

In a way, this is not very surprising. The status of P. megacephala as a pest ant in or
near structures in that region rose from the 7th spot in 1995 (Klotz et al, 1995) to the top
spot by 2007 (Warner and Scheffrahn, 2007).

It was also interesting that when I traveled to the state in 2018 to survey Key West, both of the two hotels I stayed in (one in Marathon in the Florida Keys, the other in Homestead, which is south of Miami) had P. megacephala colony clusters in them. I had found that a very remarkable coincidence at the time, but perhaps I should not have been that surprised. When I traveled to Fort Lauderdale earlier this month I also easily found the species in an urban park (I was only in the city for one day), where it and S. invicta have co-existed since at least the 1980s.

The cause of this upsurge in the species is not known, although Warner and Scheffrahn in 2007 stated it might have been because of new plantings of trees to replace those damaged due to hurricanes in that area.

Another possibility that comes to mind is that the climate in that state may be slowly changing to better accommodate the species, which is normally constrained by abiotic factors. P. megacephala prefers moisture and warmth, and is easily desiccated.

As an aside, it's kinda annoying that the ant they show in one video is not the right species, but I guess they had to show a larger ant for the cameras (even the majors in P. megacephala are small at 4 mm or less). Fortunately, the other article's video had the right species *smh*.

The two articles:

Step aside, fire ants, there’s a new, big-headed, six-legged female sheriff in town

'Bigheaded' ants are invading South Florida

Pheidole megacephala in George Town, Grand Cayman

Citation: Sunjian, A (2019). Pheidole megacephala in Georgetown, Grand Cayman . The Pm Compendium (PMC). https://pheidolemegacephala.blogspot.com/2019/03/pheidole-megacephala-in-georgetown.html

Abstract

A visual survey of the downtown area of Georgetown, Grand Cayman in March 2019 revealed the presence of Pheidole megacephala, which had been absent in previous surveys. A mapping of the current range of the colony cluster in the city showed that it occupied at least one block, an area of approximately 1 hectare. No other ant species were found in that area, although Paratrechina longicornis, a Brachymyrmex sp., Trichomyrmex  destructor, and Solenopsis invicta fire ants were present surrounding that block.

PDF of Full Article:

Pheidole megacephala in Georgetown, Grand Cayman

A survey of ants in Old Town Key West in Florida and a review of Pheidole megacephala as an archetypal “hegemonic” species

Citation: Sunjian, A (2018). A survey of ants in Old Town Key West in Florida and a review of Pheidole megacephala as an archetypal “hegemonic” species. The Pm Compendium (PMC). https://pheidolemegacephala.blogspot.com/2018/06/a-survey-of-ants-in-old-town-key-west.html

Abstract:

A two-day visual survey of Old Town Key West in Florida in May 2018 was conducted to determine the distribution of urban ants in this city. The census covered approximately 230 hectares and revealed that the area was partitioned into mutually exclusive territories by a Pheidole megacephala cluster on the northern end, and fire ant colonies (Solenopsis invicta and S. geminata) towards the south, although various other non-dominant species were also present. Only a single specimen of the formerly dominant Trichomyrmex destructor was collected during the survey, and its replacement in the city center is discussed within the context of a detailed review of the role of P. megacephala as a so-called “hegemonic species”.

PDF of Full Article:

A survey of ants in Old Town Key West in Florida and a review of Pheidole megacephala as an archetypal “hegemonic” species

Pheidole megacephala in Harare, Zimbabwe

Note Citation: Wetterer, JK (2018). Pheidole megacephala in Harare, Zimbabwe . The Pm Compendium (PMC). https://pheidolemegacephala.blogspot.com/2018/03/new-records-of-pheidole-megacephala-in.html

Dr. James Wetterer, whose research focuses on the distribution and ecology of invasive ant species, surveyed Harare in Zimbabwe, as well as the town of Kariba, and some points in between in 2012.

He noted that "at all sites in Harare and a nearby game reserve, Pheidole megacephala dominates and few other species are to be found. I don't even find other widespread tramps."

Click here for google map of P. megacephala samples.

What are colony clusters?

I noticed I used the term "colony cluster" in the latest survey, so I wanted to define what the term means.

Although P. megacephala forms supercolonies, some of which may extend for thousands of kilometers, it is unlikely that they form a spatially contiguous and continuous population over entire land masses.

In this case, I wanted to use the term "colony cluster" to refer to a discrete population of a unicolonial species that is spatially separated more or less from other clusters within the supercolony. The separation may have come about because of natural or human-mediated dispersal of a propagule, or it may have been created by the partitioning of a larger community into separate communities due to encroachment by other species or other natural events.

Based on some studies, such colony clusters can remain active and viable for decades, something which is not possible for monogyne species.

A new page in the website is now dedicated to listing maps of P. megacephala clusters and the surrounding ant communities, which will hopefully be of help to researchers studying ant distribution and ecology.

A comprehensive survey and mapping of the Pheidole megacephala colony cluster in Bridgetown, Barbados

Citation: Sunjian, A (2018). A comprehensive survey and mapping of the Pheidole megacephala colony cluster  in Bridgetown, Barbados . The Pm Compendium (PMC). https://pheidolemegacephala.blogspot.com/2018/02/a-comprehensive-survey-and-mapping-of.html

ABSTRACT

A visual survey of the downtown area of Bridgetown Barbados in January 2018 revealed the presence of Pheidole megacephala. It was the most collected species during the study, and was the only dominant ant present in the location. A mapping of the current range of this colony “cluster” showed that it extended at least from the Pelican Village Craft Center on the west to Independence Square on the east, with the northernmost limit near the James Street Methodist Church, a combined area of approximately 21 hectares. The possible introduction of this species into Barbados via a major renovation to the city port facilities in 2002 is discussed.

Click below for complete article in PDF format (revision date 2018-02-19):

A comprehensive survey and mapping of the Pheidole megacephala Colony Cluster in Bridgetown, Barbados

A Survey of the Distribution of Pheidole megacephala and Linepithema humile in Ireland Island North in Bermuda

Citation: Sunjian, A (2017). A Survey of the Distribution of Pheidole megacephala and Linepithema humile in Ireland Island North in Bermuda. The Pm Compendium (PMC). https://pheidolemegacephala.blogspot.com/2017/06/a-survey-of-distribution-of-pheidole.html

Abstract

A survey of the locations of various ant populations in North Ireland Island in Bermuda revealed that the invasive Pheidole megacephala has continued to expand its territory at the expense of the equally invasive Linepithema humile, and has now become the dominant ant in this highly-disturbed area. However, pockets of the latter ant continue to exist, including a narrow corridor of territory cutting partly across the Royal Naval Dockyard from west to east.


Click for PDF:

A Survey of the Distribution of Pheidole megacephala and Linepithema humile in North Ireland Island in Bermuda (pdf)