The Invasion Of Fire Ants

Published Date: 02 Nov 2017

Sebastian Wernecke

Ecology

Spring 2013

Dr. Dollar

Ecological impacts due to the invasion of fire ants (Solenopsis invicta) into new territories.

There has not been much investigation into the impacts that invading species have on the native wildlife areas that they are invading. Budgets have been more focused on discovering the effects that they have on agriculture and public health that have been affected, as the damages caused by these ants are esinmatied to be in the billions in the United States of America alone.

Over 205 non indigenous species have made home in the United States of America since 1980, one being the Fire Ant (Solenopsis invicta). Fire ants found their way into the United States in the late 1930s on board cargo ships from tropical South America. The ant's native habitat has been tracked down to the Paraguay-Paraná River Basin in South America. The Cargo ships arrived in Mobile, Alabama, and fire ants immediately migrated throughout the United States. These invaders have spread themselves over 104 million hectares of land in nine southeastern states. These Fire ants have also been found as far north as Delaware and as far west as California. In total they currently found in 15 of the nation's states including: Texas, Florida, Oklahoma, Nevada, Alabama, Louisiana, North and South Carolina, New Mexico, Tennessee, and Arizona. However it does not stop here, fire ants thrive in warm weather and in places with heavy hours of sunlight; and they are rapidly adapting to colder climates, which translates to more states facing the chance of infestation in the near future.

Due to these fire ants being native to South America they have no natural predators, parasites or pathogens and are not restricted by any competition. This species of ants has come to control over 5 times the amount of land they cover in their native environments, in only 75 years that they have been on North American shores.

Identification

These invading fire ants can only be distinguished through careful identification from other native fire ant species, such as the; Southern fire ant (Solenopsis xyloni), Tropical fire ant, (Solenopsis geminate) or the Desert fire ant (Solenopsis aurea) . These invading ants are typically 0.1-0.2 inches in length and have a shiny orange/red head with a shiny black abdomen. This invading species has, like other ants, antennae’s which are divided into ten segments ending in a two-segmented club like feature. The petiole (waist), which attaches the two parts of the body, namely the thorax and abdomen, also is made of two segments. Worker ants have a stinger at the tip of the abdomen that is clearly visible. http://www.allpestexpress.com/insects/Red_imported_fire_ant.gif

The Solenopsis invicta can be easily identified by its mound that it builds and makes home in. These mounds are unlike most types of ant hills; those of the invading ants have no opening in the center. The invading species leave and enter the mound using a system of underground tunnels. Each mound may contain in excess of 250,000, and in some severe cases have been over 1,000 mounds per acre.

Lastly, their nature is extremely aggressive in comparison to native fire ants. When the mound is disturbed the workers swarm out and attempt to sting the intruders, usually leaving white fluid filled blisters due to their distinctive venom that they inject immediately after being in contact with the intruder.

Inhabitance coverage in the USA

As one can see, from the image above, these fire ants have invaded almost a quarter of the land within the United States of American in just less than 100 years since their introduction into the country. This invasion equates to just less than 70 square kilometers of land being inhabited on average every day for the past 97 years.

Potential red imported fire ant range expansionRange expansion legend

This second image has the improbable, undetermined, possible and certain areas of land that will be invaded by fire ants. The key to the right indicates the point markers and their significance on the map. The threat is continual, Fire Ants are constantly being found in new territories. Recently Fire ants have been found in Central Indiana, with no certain source as to their method of invasion. This throws over 1000 kilometres of land between known invaded lands and this new invasion point. Only human kind could be the transportation method of this invasion. It is estimated that these ants will eventually colonize over 50% of the terrestrial surface of the Earth ****************************

Impacts on the Native Fence Lizards

The impacts that these fire ants have had on native wildlife is not very well known basically due to the lack of base comparative data and the difficulties that come with that logistically. However a more in depth investigation was carried out by the ESA (Ecological Society of America) into the affects these Fire Ants have had on Native Fence Lizards (Sceloporus undulates) which can lead the way for new studies.

In this investigation the main point being examined is the adaptive response of a native lizard to the invasion of the venomous fire ant.

These ants are extremely aggressive. They attack in a unique manner and have strategy to defend their nest as well as to capture their prey with. They swarm tens to hundreds and in some cases thousands of ants will horde an intruder or prey animal and sting the victim multiple times, this can even overpower large mammals.

This study was carried out across the Southern cusp of the United States. Four sites were created to conduct the investigation. These sites being:

St Francis National Forest, Lee County, Arkansas (34?43/50// N, 90?42'18" W);

Highway 35, in Panola and Talla hatchie Counties, Mississippi (34?16'43" N, 90?02'06" W);

Noxubee National Wildlife Refuge, Winston County, Mississippi (33?20'32" N, 88?54'07" W);

Solon Dixon Forestry Education Center, Escambia County, Alabama (31?09'49" N, 86?42'10" W) *************************************************

Each of these sites has had different backgrounds with fire ant invasion. Site 1 hasn’t been invaded, Site 2 was invaded 23 years ago, Site 3 was invaded 54 years ago and site number 4 was invaded 68 years ago.

Each of the sites is found in the same eco-region. The WWF classification defines an ecoregion as: "A large area of land or water that contains a geographically distinct assemblage of natural communities that:

(a) Share a large majority of their species and ecological dynamics;

(b) Share similar environmental conditions, and;

(c) Interact ecologically in ways that are critical for their long-term persistence."

Within each of these eco regions adult and juvenile lizards were found to be used. 20 Adult and 20 juvenile lizards, from each site, were picked up and collected for use in this study. The next year the eggs, from the picked lizards were collected from two of the 4 sites: the uninvaded site (Site 1, 16 females) and the one invaded longest ago (Site 4, 18 females)*********. These eggs were incubated in moist conditions until hatching, and approximately 59 days later 157 juveniles hatched from Site 1 and 128 juveniles from Site 4. All of the juveniles were kept in controlled conditions until they were mature enough for testing. The hatchlings were housed in an enclosure of dimensions 30cm X 20cm X 25cm, with 5 individual juveniles per enclosure. "Lined with paper toweling and furnished with a shelter, water bowl, and heat source."

Once mature enough, each of the lizards was individually attached by a 1m piece of cotton to a peg that was stationed 40cm from a large, active Invasive Fire Ant mound. The lizards were encouraged to walk/run onto the mound by control of the cotton thread. The interaction and response, on the lizard’s part, was very important into the consequences of the ant’s attack that would follow. Based on pilot data, some lizards were exposed to below-lethal levels of fire ants (7.44 ants/adult lizard, 95% CI = 6.88-8.01, and 2.04 ants/juvenile lizard, 95% CI = 1.83-2.25). The testing was to see whether "lizards behaviorally respond to reduce the consequences of attack by fire ants, and whether this response changes with time since invasion". Each of these tests lasted a maximum of 60 seconds for the adults, and 30 seconds for the juveniles, that is if the lizard had not yet already used evasive maneuvers to leave the point of attack. The ants swarmed in numbers that were within the range of the natural attack numbers on these lizards. The test would begin as the first fire ant climbed upon the lizard, any body twitches or any other retaliation was recorded as well as the average number ants that were attacking was recorded. Foraging behavior of fire ants is affected by temperature thus the nests temperature was also recorded at the beginning of each test.

Results from these tests show the impacts these ants have had on this species over the years. The behaviors, ranging from fleeing to body twitches that were revealed by the fence lizards in response to attacks by fire ants lower the risk of mortality if these responses can lower the lizard’s time in the presence of the attacking ants. The number and percentage of adult and juvenile lizards that demonstrated either of the two actions: body twitches or fleeing behavior was accounted for.

From the insert above from********************************************. One can see the gradual increase from Site 1 (has not been invaded) to Site 4 (invaded 68 years previous to test) of the percentage of lizards that fled and/or had body twitches to fling off the ants.

The solid shapes represent body twitch and flee defensive behavior in the presence of fire ants, whilst the open shapes represent test controls, behaviors surveyed during trials that were conducted without the presence of fire ants.

Lizards that fled increased in numbers from +- 40% (Site 1) to +-80% (Site 4) for adults and for juveniles the reaction to flee increased minimally. Lizards that demonstrated body twitches increased from +- 45% to +- 90% from sites 1-4 respectively, and once again for juveniles this reaction was very minimal in testing. The juveniles did not display such large changes in their reactions due to possibility of not having to demonstrate such large numbers of increase because of an increase in hind leg length which will be discussed further below.

The other aspect that was looked into was the development of longer hind limbs of the lizards the longer they had been exposed to the red fire ants.

The above image from ********************************* illustrates the gradual increase of the lizards relative hind leg lengths. The adult lizards limb lengths increased in length from 0.3975 inch to 0.41 inch from site 1 to 4, this is a 3.1% increase in limb lengths in the time frames of the invasion. For juveniles their limb lengths increased from .40inch to .42inches in length, this is a 5% increase over the time frame, thus illustrating the Darwin theory of survival of the fittest, the longer limbed lizards are surviving and passing on their genes to the next generation.

One possible theory behind this change in hind leg length is that this increase would help minimize the amount of venom the ants could inject into a lizard. Longer hind limbs improve the efficiency of the body-twitch and obviously allows for faster retreating on the lizards part. This flee tactic also helps dislodge attacking fire ants, which reduces the time for "envenomation" to occur.

Other Impacts

Fire Ants can completely eliminate ground-nesting

birds in a given area. The northern bobwhite quail

(Colinus virginianus; Figure 6), an important game

species, has been the focus of much research on the

impacts of RIFA. RIFA may be one of the reasons

for the observed decline in quail numbers in Florida

and across much of the southeastern U.S. over the

past 10 years. RIFA impact bobwhite quail by

stinging and consuming piping young. Even after

they hatch, individuals stung by fire ants have

reduced survival. In one study, 38% of bobwhite

chick deaths were attributed to RIFA stings. If chicks

do survive being stung, their growth is often stunted,

resulting in a lower body mass. A lower body mass

Red Imported Fire Ants and Their Impacts on Wildlife 5

can potentially increase their risk of mortality from

other factors such as predation, disease, starvation, or

exposure.

Loggerhead shrike (Lanius ludovicianus)

numbers are also often lower in habitats invaded by

fire ants. These declines may be a result of

competition with RIFA for food, primarily insects.

RIFA have also been reported causing mortality and

declines in barn swallows (Hirundo rustica), crested

caracaras (Caracara plancus), common ground doves

(Columbina passerine), blue-grey gnatcatchers

(Polioptila caerulea), eastern towhees (Pipilo

erythrophthalamus), indigo buntings (Passerine

cyanea), northern cardinals (Cardinalis cardinalis),

and yellow-billed cuckoos (Coccyzus americanus) in

certain areas. The causes of mortality and reasons for

decline vary between species but are usually a result

of stinging, predation of young, or competition for

food resources.

Waterbirds such as the least tern (Sterna

antillarum), great egret (Casmerodius albus), snowy

egret (Egretta thula), roseate spoonbill (Ajara ajara),

laughing gull (Larus atricilla), black rail (Laterallus

jamaicensis), great blue heron (Ardea herodis), and

tricolored heron (Egretta tricolor), all of which can

be found in Florida, can also be severely impacted by

RIFA. One Texas study showed that, during the

warm summer months of June and July when RIFA

are most active, ant infestation was responsible for up

to a 92% reduction in offspring survival of many of

these waterbirds.

Impacts on Mammals

The impacts of fire ants on mammals have been

most clearly documented in deer. The presence of

RIFA in an area reduces the number of deer fawns

surviving to maturity. In the presence of danger, deer

fawns freeze. This allows RIFA to attack, causing

blindness or debilitating injury (Figure 7). The

irritation caused by RIFA stings may also result in

increased fawn movements, heightening their risk of

predation by animals such as the coyote. If increased

movement occurs during the day when fawns would

normally remain hidden, this could further increase

their predation risk. Similar effects on the young of

other mammal species could be possible. RIFA are

also thought to be a threat to small mammals such as

mice, voles, and squirrels due to their small size and

tendency of many to live below ground.

Figure 7. Deer fawn with scars on its head from red

imported fire ant stings. Credits: B.M. Drees, Texas A and

M University (2004).

For additional information on RIFA impacts on

wildlife:

C.R. Allen, D.M. Epperson and A.S. Garmestani.

2004. Red imported fire ant impacts on wildlife: A

decade of research. American Midland Naturalist.

152: 88-103

http://fireant.tamu.edu/materials/factsheets_pubs

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http://www.extension.org/pages/42431/are-fire-ants-native-to-north-america

Korzukhin, M. D., S. D. Porter, L. C. Thompson. "Imported Fire Ant and Household Insects : Potential United States Range Expansion of the Invasive Fire Ant." Imported Fire Ant and Household Insects : Potential United States Range Expansion of the Invasive Fire Ant. N.p., 10 May 2006. Web. 30 Mar. 2013.****MAP potential

Harold, Allison. "Fire Ants Are Invading Indiana." Heraldtimesonline.com. N.p., 17 Mar. 2013. Web. 30 Mar. 2013.