Southern fire ant

Scientific name

Solenopsis xyloni (Hymenoptera: Formicidae)

Other common names

California fire ant, cotton ant

Similar species

red imported fire ant, Solenopsis invicta

native fire ant, Solenopsis geminata
Heads of the workers of the southern fire ant, Solenopsis xyloni are not as disproportionately large as those of workers of Solenopsis geminata.

Distribution

United States: Alabama, Arizona, California, Georgia, Kansas, Louisiana, Mississippi, Nevada, New Mexico, North Carolina, South Carolina, Tennessee, and Texas.

Worldwide: Mexico.

Native to the southern United States and Mexico.

Diagnostic characteristics

Nests

• Build loose mounds near the bottom of tree trunks.

Adults

• Yellowish-red headhead:
  one of the three main body segments in insects; the anterior-most segment containing the many sensory structures including the eyes, antennae, and mouthparts
  and thoraxthorax:
  one of the three main body segments in an insect, located between the head and abdomen, where the wings and legs of the insect attach
  , black abdomenabdomen:
  one of the three body segments in insects; the most posterior segment containing the heart, reproductive organs, and digestive organs
  (gaster). They may also be completely orangeish-red or brownish-black.
• 10-segmented antennae with a 2-segmented club.
• Hairy abdomenabdomen:
  one of the three body segments in insects; the most posterior segment containing the heart, reproductive organs, and digestive organs
  .

Pupae

• Occur in underground nest, only seen when mound is disturbed.
• Resemble adults with legs and antennae held close to body.
• Initially appear white with black eye-spots.
• Color of pupae darkens with age.

Larvae

• Occur in underground nest, only seen when mound is disturbed.
• Four larval stages.
• White, grub-like larvae.
• Fourth instarinstar:
  immature stages (larva or nymph) of insects in between molts
  larvae are the only stage capable of ingesting solid food.

Eggs

• Occur in underground nest, only seen when mound is disturbed.
• White in color.
• Difficult to see without magnification.

Hosts

Citrus hosts

All Citrus species and their hybrids.

Non-citrus hosts

Not a direct pest but is disruptive in agricultural production.

Host damage

Flowers

• Feed on flowers.

Fruits

• Damage young, developing fruit.

Trunk

• Chew on the bark and cambium of young trees to feed on sap.
• Can girdle and kill young trees.

Twigs

• Chew twigs of newly planted, young trees.
• Chew off new growth.

Other

• May nest in and plug irrigation lines.
• Indirectly harm citrus by protecting honeydew-secreting insect pests from natural enemies. This protection can disrupt biological control programs targeting honeydew-secreting insects and result in larger populations of pest species including scales, aphids, whiteflies, etc.
• Shown to preferentially attack some parasitized pest species, resulting in disruption of biological control programs of pest species like the California red scale.

Biology

Mating flights are the primary means of ant colony propagation. Colonies generally contain a few large workers (major workers), many medium-sized workers (media workers), and a majority of small workers (minor workers). The three types of workers are all sterile females and serve to perform tasks necessary to maintain the colony. The queen (or queens) is the single producer of eggs. The diet of foraging workers consists of dead animals, including insects, earthworms, and vertebrates. Workers also collect honeydewhoneydew:
the sugar-rich waste product excreted by aphids, mealybugs, and scales insects as a result of feeding on the phloem of plants
and store seeds. Larvae are fed only a liquid diet until they reach the third instarinstar:
immature stages (larva or nymph) of insects in between molts
. When the larvae reach the fourth instarinstar:
immature stages (larva or nymph) of insects in between molts
, they are able to digest solid foods. Worker ants will bring solid food rich in protein and deposit it in a depression in front of the mouth of the larvae. The larvae will secrete digestive enzymes that break down the solid food and regurgitate it back to worker ants.

Comments

Identification of fire ants in the genus Solenopsis is difficult and requires evaluating a series of different-sized workers. In addition, members of this genus are known to interbreed.

The southern fire ant is a generalist predator. Therefore, the presence of the ant may be beneficial when consuming certain pest species. However, the southern fire ant is viewed as a pest based on other negative impacts they may have on agricultural operations.

References

Martinez-Ferrer, M.T., E.E. Grafton-Cardwell, and H.H. Shorey. 2003. Disruption of parasitism of the California red scale (Homoptera: Diaspididae) by three ant species (Hymenoptera: Formicidae). Biological Control 26(3): 279-286. (doi:10.1016/S1049-9644(02)00158-5).

Manaaki Whenua - Landcare Research New Zealand. 2012. Invasiveinvasive:
term used to describe species that are not native and have the ability to adversely effect habitats they invade either ecologically or economically
ant threat: Solenopsis xyloni. Information sheet #29. (http://www.landcareresearch.co.nz/research/biocons/invertebrates/Ants/invasive_ants/documents/29.pdf).

Authors

Weeks, J.A., A.C. Hodges, and N.C. Leppla