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Introduction:
The bigheaded ant (BHA),
Pheidole megacephala (Fabricius), is a very successful invasive species that
is sometimes considered a danger to native ants and has been nominated as among
100 of the "World's Worst" invaders (Hoffman 2006).
The BHA has been a pest in southern Florida
for many years, and according to reports by pest control operators, it is
becoming an even more pervasive nuisance as it displaces other ants, such as the
red imported fire ant (RIFA), Solenopsis invicta Buren, and the
white-footed ant Technomyrmex albipes (Fr. Smith) in some areas. It is
possible that the increase in BHA infestations was augmented by several years of
excessive hurricane activity (2003 to 2005) in Florida that damaged lawns and
killed trees which necessitated the use of increased amounts of sod and other
replacement vegetation that may have been infested with this ant (Warner,
unpublished observation). The BHA does not sting or cause any structural damage,
and usually does not bite unless the nest is disturbed, and even then, the bite
is not painful. There are some 17 Pheidole species in Florida of which 14
are native to Florida (Deyrup 2003).
 The BHA, a soil-nesting ant, is sometimes
confused with subterranean termites because it may create debris-covered
foraging tubes that are somewhat similar, albeit much more fragile, than termite
tubes. More often these ants leave piles of loose sandy soil. Homeowners
are annoyed by these "dirt piles" and by ants foraging in bathrooms, kitchens,
around doors, and windows, as well as on exterior paved or brick walkways or
driveways. Control of the BHA is difficult because the ant colonies are
numerous and populations usually extend across property lines.
Originally recorded from the Indian Ocean
island of Mauritius (Fabricius 1793), the BHA is a widespread invasive tramp ant
found in many subtropical and tropical regions throughout the world. Original
reports of BHA in Florida mention Everglades, Key West and St. Augustine (Smith
1933).
More recently the BHA has been confirmed in
Alachua, Brevard, Broward, Charlotte, Collier, Dade, Dixie, Highlands,
Hillsborough, Indian River, Lee, Monroe, Palm Beach, Pinellas, Sarasota,
Seminole, and Volusia Counties (Ferster et al. 2000, Deyrup 2003).
Workers are dimorphic (major and minor
workers). The BHA receives its common name from the large-sized head of the
major worker, or "soldier." Minor workers are small (2 mm) reddish brown ants.
The majors are much larger (3 to 4 mm), but only constitute about 1% of
foragers. The front half of the major's head is sculptured, while the back half
is smooth and shiny. The petiole (waist) of both worker forms is two-segmented
and the post-petiolar node is conspicuously swollen. The antenna is
twelve-segmented with a three-segmented club. The entire body is covered with
sparse, long hairs. Workers have a pair of short propodeal spines (spines on
waist) facing almost directly upward. There is usually a dark spot on the
underside of the gaster.
The RIFA is sometimes confused with the BHA,
but the RIFA has polymorphic (many sized) workers and the BHA is dimorphic. (See
nest differences below.) When disturbed, the RIFA is highly aggressive and will
bite and sting, while the BHA bites but does not sting. The BHA is slightly
smaller, darker colored, and less shiny than RIFA. Both nest in the soil.
The BHA is omnivorous, feeding on sweet
liquids such as honeydews, dead insects, and soil invertebrates. Foragers will
quickly recruit nest mates to a food source. Foraging tunnels having numerous
entrances can be seen along the soil surface. Arthropod prey are dissected by
workers and brought back to the nest.
Trails of foragers can often be observed along
trees trunks, sometimes climbing into canopies of tall trees. Similar trails
might be seen on the exterior walls of structures as ants climb into attics or
other natural or artificial voids.
Trophallaxis (an exchange of food between
ants) is frequently observed between two minor workers, or a minor and major
worker.
The BHA can be found nesting in disturbed
soils, lawns, flowerbeds, under objects, such as bricks, cement slabs, or flower
pots, around trees or water pipes, along the base of structures, and walkways,
where displaced soil is usually observed from the action of ants digging below
the surface. Well-cared-for lawns may have BHA infestations that are less
noticeable, except along the edges where lawns meet walkways where piles of soil
are often deposited. BHA populations expand into neighboring areas by following
along these lawn-walkway edges or roadways. Population movements into new areas
to establish nests and subsequent displacement of other ant populations can be
rapid (Hoffman 2006; Warner, unpublished observations).
Pest Status
A new survey of pest ants in Florida has not
been done, but at least in southeastern Florida, the white-footed ant can be
added, and the status of the BHA has increased. Perhaps the order of the top
nine most problematic pest ant species in and near structures (South Florida
2007) might be:
- bigheaded ant
- white-footed ant,
Technomyrmex albipes (Fr. Smith)
- ghost ant
- red imported fire ant
- crazy ant (Paratrechina
spp.)
- Florida carpenter ant
- Tortugas carpenter ant
- Pharaoh ant
- rover ant, Brachymyrmex
spp.
References:
http://creatures.ifas.ufl.edu/urban/ants/bigheaded_ant.htm
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