Ant Twin Oaks Valley

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Ants Of Twin Oaks Valley
© W.P. Armstrong 18 March 2018
      Index Of Ant Genera On Wayne's Word       Ant Genera Photographed By Alex Wild  

Twin Oaks Valley runs north and south. It lies roughly between the Merriam Mtns and Owens Peak. These two mountains are only a few miles apart at their closest distance.
  16 Ant Species On Owens Pk (Ant Introduction Page)  
More Images Of Ants In The Nearby Merriam Mtns

14 species caught in pitfall traps & middens near mailbox in bridle path at front of my house. All of these were collected within a radius of 20 ft! This remarkable number is the greatest ant diversity in a relatively small area in all of my ant expeditions! A: Solenopsis cf. amblychila queen, B: Pheidole cf. californica major & minor workers, C: Solenopsis molesta queen, D. Cyphomyrmex wheelei, E. Hypoponera opacior, F. Dorymyrmex insanus, G. Strumigenys cf. rogeri, H. Strumigenys membranifera, I. Linepithema humile, J. Forelius mccooki, K. Cardiocondyla mauritanica, L. Solenopsis xyloni, M. Brachymyrmex patagonicus, N. Strumigenys louisianae. For more information and images of all species please refer to the following table:
  My Beautiful Painted Mailbox!  

A Total of 20 Ant Species in Twin Oaks Valley
14 Out of 20 in 1/2 Acre Plot At My Home In Twin Oaks Valley
14 Out of 20 Within 20 ft. Radius In Bridle Path At My House!

* Found in 1/2 acre plot at my home in Twin Oaks Valley
  1. *Cardiocondyla mauritanica Found In Forelius mccooki Midden
  2. *Minute Solenopsis (Similar To S. tennessensis or S. molesta 
  3. *Fire Ant Queen (Solenopsis molesta) Found in My Bathroom
  4. *Fire Ant (Solenopsis xyloni) Found On Bridle Path
  5. *Forelius mccooki Active Nests On Bridle Path
  6. *Fungus Farming Ant (Cyphomyrmex wheeleri
  7. *Miniature Trap-Jaw Ant (Strumigenys louisianae)
  8. *Miniature Trap-Jaw Ant (Strumigenys undetermined)
  9. *A 3rd Species of Strumigenys: Possibly S. membranifera
  10. *Black Pyramid Ant (Dorymyrmex insanus) Bridle Path
  11. *Argentine Ant (Linepithema humile) Bridle Path & Home
  12. *Rover Ant (Brachymyrmex cf. patagonicus) Twin Oaks Valley
  13. *Big-Headed Ant Ant (Pheidole cf. californica) Twin Oaks Valley
  14. *Hypoponera opacior: Unusual Subterranean Ant In Bridle Path

    Other Species Found Along the Lower Slopes of Merriam
    Mountains and Owens Peak That Border Twin Oaks Valley

  15.  Honeypot Ant (cf. Myrmecocystus wheeleri) Merriam Mtns
  16.  Honeypot Ant (cf. Myrmecocystus testaceus) Owens Peak
  17.  Red Harvester Ant (Pogonomyrmex subnitidus) Merriam Mtns
  18.  Black Harvester Ant (Veromessor andrei) Merriam Mtns & Owens Pk
  19.  Orange Desert Ant (Forelius pruinosus) Bridle Path Near My Home
  20.  Big-Headed Ant (Pheidole vistana) Lower Slopes of Owens Peak

  Disclaimer: I am reasonably certain about most of the identifications, especially those verified by James Trager, Alex Wild & Phil Ward. For some of the names I used cf. (compare with) because of the difficulty in separating very similar species. On others I simply placed the ants in their respective subgroups of closely-related species. Large, difficult genera often require a specialist for precise species verification. Although identifications from my photo images may be impossible without voucher specimens to examine, comments and/or suggestions about my identifications are welcome.
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Linepithema humile
Most of these species were found at my residence in Twin Oaks Valley, San Marcos which is dominated by massive populations of the aggressive Argentine ant (Linepithema humile). In fact, I was very surprised to find additional ant species here, including some unusual tropical species. They were collected in pitfall traps placed along a bridle path and in the midden (graveyard) of a Forelius mccooki nest.

Twin Oaks Valley East Of Owens Peak

1. Myrmicinae: Cardiocondyla cf. mauritanica

Like the duckweeds (Lemnoideae), ants have been renamed by taxonomists over the decades even when the species was already officially named & published decades or centuries before. For example, the name Cardiocondyla ectopia appears in a detailed USGS ant survey in Orange County just north of Twin Oaks Valley, Northern San Diego County. According to, C. ectopia is a junior synonym of C. mauritanica. In other words, it is a synonym that describes the previously published C. mauritanica. For this and other morphological reasons, I am calling the Twin Oaks Valley species Cardiocondyla cf. mauritanica. Ideally I should place cf. (compare with) before the species epithet because I am not 100% certain of its ID. Some ants are very difficult to identify, especially minute species with characteristics beyond the range of my magnifying devises!

Forelius mccooki nest and midden in Bridle Path of Twin Oaks Valley, San Marcos. The midden consists of ant and other arthropod body parts (mostly heads) resemblling a pile of pepper grains near their nest. Some of the ant species discussed on this page were actually found in this midden. See following image.

Sample from Forelius mccooki midden in Twin Oaks Valley, San Marcos. Two Cardiocondyla mauritanica workers are shown by red arrows.

Minute Cardiocondylla mauritanica Worker From Forelius mccooki Ant Midden

The "eye" of an ordinary sewing needle shows the small size of a Cardiocondyla mauritanica worker. This ant was collected in the midden (cemetary) of a Forelius mccooki nest in Twin Oaks Valley, San Marcos.

The above image of Cardiocondyla mauritanica clearly shows this species lacks the dorsal standing pilosity (erect hairs) of Temnothorax. This is a widespread species with an enormous native distribution from northwest Africa to India. It has been suggested that one of the reasons for its success in spreading throughout the Old and New Worlds is its ability to co-exist with dominant invasive species such as the Argentine ant (Linepthema humile). Argentine ants were observed to shrink back when encountering Cardiocondyla workers, suggesting that they may release an effective and potent chemical repellant.

The common name "moorish sneaking ant" has been proposed for this genus, apparently due to their inconspicuous nature. The specific epithet mauritanica is Latin for "Moorish." The term "Moor" is derived from the Mauri people of northwestern Africa, and has long been used in Europe as a colloquial term for inhabitants of North Africa. When viewed from above, the postpetiole is much broader than the petiole and is roughly heart-shaped, hence the generic name Cardiocondyla.

Compared with most tramp ants, the colonies are relatively small with a few hundred workers and multiple queens. Many ant species exhibit polymorphism in workers, with different sized minor and major workers. Cardiocondyla has polymorphism in males, a rarity in ant species. This condition is technically termed polyphenism: Two or more distinct phenotypes are produced from the same genotype, a compelling reason to study epigenetics! In Cardiocondyla there are winged males that leave the nest to mate with winged queens (alate females) from other colonies, and wingless fighter males that mate with female sexuals (queens & workers) within their natal nest.

The following description of wingless fighting males is from:

Jürgen Heinze. 2016. Life-History Evolution in Ants: The Case of Cardiocondyla. Proc Biol Sci. 2017 Mar 15; 284(1850): 20161406. Published online 2017 Mar 15. doi: 10.1098/rspb.2016.1406:

Click Here To Read This Fascinating Article By Jürgen Heinze

"While winged males are docile, fragile dispersers, wingless males are robust and equipped with strong mandibles. Intrasexual competition among wingless males may be extremely fierce and in many species results in obligate lethal fighting. Wingless males have strong, shear-shaped mandibles in one of the two basal branches of the phylogeny, and long, sabre-shaped mandibles in the other. They use their mandibles to eliminate freshly emerged competitors by crushing or piercing the still soft cuticula of the latter. In addition, males with sickle-shaped mandibles may grab rivals that have survived the first few critical hours of their adult lives and to besmear them with hindgut secretions, which elicit aggression from workers against the so branded individual. This basic scheme of deadly male combat is modified in numerous ways. For example, fighting among adult males appears to be less common in most species with shear-shaped mandibles, probably because these are less suitable for grabbing sclerotized, adult rivals."

Cardiocondyla wingless fighter male showing sickle-shaped mandibles used for killing other wingless males in nest. Docile winged males are not harmed. Image from Jürgen Heinze (2016).

More Images In Article By Jürgen Heinze

Cardiocondylla mauritanica Winged Male

My image of male Cardiocondyla mauritanica from Forelius mccooki midden is very similar to image of C. emeryi. The large compound eyes and 13 segmented antennae are characteristic of winged male Cardiocondyla.

cf. Cardiocondylla mauritanica Winged Queen

Cardiocondyla mauritanica winged queen (alate female) .

2. Solenopsis undetermined (resembles AntWiki images of S. tennesseensis)

The tiny ant in center resembles AntWiki images of Solenopsis tennesseensis. Unfortunately, this specimen is missing its antennae. Hopefully, I can find another specimen that is intact. There are minute, erect hairs on scape of Forelius (visible under 80x magnification). This species identified as F. mccooki by Phil Ward.

3. Subfamily Myrmicinae: Thief Ant Queen (Solenopsis molesta)

A queen thief ant (Solenopsis molesta) appeared in my home on 17 April 2015. Due to the high concentration of well-established Argentine ants, it is doubtful that a new colony of this species could become established. This queen was about 4.2 mm long, smaller than fire ant queens of S. xyloni and S. invicta.
On 12 July 2018 I found another Solenopsis queen in a pitfall trap in the bridle path in front of my home in Twin Oaks Valley. It was larger than a S. molesta queen, but smaller and more orange-red than a S. xyloni queen. I tentatively identified it as Solenopsis amblychila. I will not count this species until I confirm its identity.

  Solenopsis amblychila at Daley Ranch in Nearby Escondido  

4. Myrmicinae: Solenopsis xyloni

Solenopsis molesta: A Minute Ant That Resembles Cardiocondyla!

These similar-appearing ant species have some significant taxonomic differences.

The 2-segmented antennal club, stinger and lack of propodeal spines clearly rules out Cardiocondyla. Thief ants of the Solenopsis molesta complex can be yellow to brown. Their common name is dervived from their habit of invading and stealing from nests of other species.

Although not a major morphological difference, the body of Solenopsis molesta is shinier than Cardiocondyla mauritanica; however, its 2-segmented antennal club and lack of propodeal spines are significant differences in ant taxonomy.

5. Dolichoderinae: Forelius mccooki

Forelius mccooki at nest entrance in Twin Oaks Valley (July 2017). White arrow shows erect hairs on scape of worker ant. Most of the Forelius I have seen on my field trips were F. pruinosus, unless I didn't examine their scapes carefully.

This image was taken with a compound microscope using the 10x objective and substage lighting. The 10x eyepiece was replaced with a Sony W-300 point & shoot camera; therefore, the total magnification was not exaclty 100x (10x eyepiece multiplied by 10x objective). The camera essentially replaced the eye piece. The antenna of this Forelius was covered with dense, appressed hairs. The scape had erect, straight hairs characteristic of F. mccooki.

6. Myrmicinae: Cyphomyrmex wheeleri

Another Remarkable Discovery In Forelius mccooki Midden
The Minute Fungus-Farming Ant (Cyphomyrmex wheeleri)

My images compare favorably with the image from and Alex Wild, so I am reasonably certain that the species is Cyphomyrmex wheeleri. I never would have expected this minute fungus-farming ant in a Forelius mccooki midden. I also would never have expected this unusual ant in the bridle path of a housing development!

Live Cyphomyrmex wheeleri caught in pitfall trap.

This small ant is about 2 - 2.5 mm in length. It belongs to the subfamily Myrmicinae (tribe Attini) and includes the larger Arizona leafcutters Acromyrmex & Trachymyrmex, and the tropical leafcutters Atta. Like the larger leafcutters, Cyphomyrmex is a fungus-gardening ant. It carries organic material such as insect droppings and pieces of plants back to its nest, using the material as a food for their fungus gardens. The ants then eat the fungus that they cultivate on the debris.Their garden consists of a particular fungal species that these ants have been cultivating for millions of years!

According to this species was foraging in the leaf litter along the path at the Arizona Sonora Desert Museum on an overcast day. They were quite small and difficult to see. All Cyphomyrmex species cultivate badisiomycete fungi in the tribe Leucocoprineae. In the rimosus group of attine ants, most species grow fungi in a yeast form (small masses of unicellular fungal cells) rather than in the multicellular mycelial form typical for all other attine ant gardens. Although they belong to the rimosus group, Cyphomyrmex wheeleri are known to cultivate mycelium gardens rather than yeast gardens. As I stated above, I was very surprized to find this ant at my home in Twin Oaks Valley, San Diego County, Calif.

Natasha J. M Ehdiabadi & Ted R. Schultz 2009. Natural History and Phylogeny of the Fungus-Farming Ants (Hymenoptera: Formicidae: Myrmicinae: Attini). Myrmecol. News 13: 37-55 (online 27 November 2009) ISSN 1994-4136 (print), ISSN 1997-3500 (online).

Arizona Leafcutter Ant (Large Ant the Size Of A Harvester Ant)

Arizona leafcutter ant from a large nest under a palo verde (Cercidium microphyllum = Parkinsonia microphylla): The state tree of Arizona.

  See Images Of Other Leaf-Cutter Ants On Ant Introduction Page  

7. Myrmicinae: Strumigenys louisianae
A Truly Miniature Trap-Jaw Ant

In A Forelius mccooki Midden In Twin Oaks Valley 16 August 2017

Note: This is a minute and very interesting ant discovery for Twin Oaks Valley in the City of San Marcos, northern San Diego County. It is especially interesting because it was discovered in the midden of a Forelius mccooki nest! The head is only 0.5 mm in length. It is beyond the macro range of my Nikon D-90 camera with 60mm Micro Nikkor AF-2 F/2.8 G macro lens, including a Kenko Extension Tube Set plus Canon 58mm Close-up Lens 250D. I just can't get a clean, sharp image. Perhaps this collection of lenses and extension tubes do not work that well together. Actually, my best head shot (see below) is with a Bausch & Lomb microscope at 70x.

The light spots on front of head are caused by flattened (expanded) hairs.

Another minute ant found in a Forelius mccooki midden. It resembled Strumigenys louisiana and was verified by Phil Ward at UC Davis. This is a tiny predator that feeds on springtails (insect order Collembola). The long, slender mandibles with teeth at apex are nicely adapted for quickly grasping springtails before they jump. This species has a large New World distribution: Arizona, midwest & gulf states south through Mexico, Central and South America. This species is truly a miniature version of the trap-jaw ant (Odontomachus)! It is certainly one of the most interesting ants I have ever found.

This is one of the most difficult ants that I have ever attempted to photograph. Since I only had one very fragile, deceased specimen from a Forelius mccooki midden, I could not rearrange its shape to get more depth of field or a better viewing position. In its slightly folded position the body length was less than 2.0 mm.

The entire body of Strumigenys louisianae is shorter than the mandible of the Costa Rican trap-jaw ant (Odontomachus bauri)!

8. Myrmicinae: Undetermined Strumigenys species cf. S. rogeri?

Head of undetermined Strumigenys sp. found in Forelius mccooki midden (22 Aug 2017). The hairs on front of head are not flattened and expanded as in above images of Strumigenys louisianae. Photographed through Bausch & Lomb dissecting microscope with Sony W-300 camera. See next image (pitfall collection 14 July 2018).

Strumigenys Collection 14 July 2018 cf. S. rogeri?

The above two images were taken about a year apart (August 2017 & July 2018) from a head found in a Forelius mccooki midden and an impoverished specimen found in a pitfall trap. Both were found in the bridle path in front of my home in Twin Oaks Valley, City of San Marcos, San Diego County, CA. The number of antennal segments appears to be 5, although they are not all clearly discernible in my image. Using the AntWiki Key To US Strumigenys it appears close to S. rogeri or the S. rogeri complex; however, I have not verified this tentative ID.

  See Images Of The Trap-Jaw Ant (Odontomachus)  

The following is from The Ants by Bert Hölldobler and Edward O. Wilson (1990). When attacking collembolans, the mandibles of Strumigenys louisiana are extremely long and operate very much like a miniature spring trap similar to a trap-jaw ant: "Prior to the strike the mandibles are locked at nearly 180 degrees. This position is accomplished by special teeth at their bases that catch on the lateral lobes of the labrum. When the ants tense the retractor muscles alone the mandibles cannot move, but when the lateral lobes are also dropped the mandibles snap shut. The worker Strumigenys approaching a collembolan moves slowly and cautiously. She spreads her mandibles to the maximum angle and exposes two long hairs that arise from the paired lateral lobes. These hairs extend far forward of the ant's head and serve as tactile range finders for the mandibles. When they first touch the prey, its body is well within reach of the apical teeth. A sudden and impulsive snap of the mandibles literally impales it on the teeth, so that drops of hemolymph often well out of the punctures. If the collembolan is small relative to the Strumigenys, the ant lifts it into the air and then may sting it. All but the largest collembolans are quickly immobilized by this sequence of actions, and struggling is feeble and brief."

Left: Soil springtails compared with the "eye" of an ordinary sewing needle. They are actually colorless and about 1.0 to 1.5 mm long; however, backlighting makes them appear darker. With their springing device or furcula they can jump about 100 times their body length or about 7-8 inches (18-20 cm). Although they are abundant in some soils, they are barely visible with the naked eye. In just one handful of grassland soil there can be literally thousands of individuals representing hundreds of different species.
Left: Magnified view of a soil springtail taken with a Bausch & Lomb dissecting microscope and Sony W-300 camera. The springing device (furcula) is clearly visible on the ventral side of posterior end. A handful of soil can contain literally hundreds (or thousands) of springtails. Because of their small size and colorless bodies they are difficult to see with the naked eye. In order to acheive a more accurate rendition of its colorless body, I used backlighting and then "invert" with Adobe Photoshop.

9. Myrmicinae: A 3rd Species Of Strumigenys (cf. S. membranifera)

Based on its 2-segmented club, I originally and incorrectly thought this was a minute species Solenopsis. After carefully examining its head on the advise of James Trager I can clearly see that it is Strumigenys. This is Strumigenys species #3 found in my Forelius mccooki midden at my home in Twin Oaks Valley! See following image:

To my surprise I found a third species of Strumigenys in my trusty Forelius mccooki midden! This species has shorter, triangular-shaped mandibles and is quite different from the previous two Strumigenys species. It resembles images of S. membranifera and may be that species. It has a remarkable world-wide distribution, including North & Central America, Europe, Africa, Madagascar, Mideast, Asia, Australia, and California. Some of these minute "micro-ants" that I have found in my yard may have been introduced with imported plants. They apparently have small colonies, and considering their very small size, they could easily be transported in potted plants.

Strumigenys photographed through Olympus compound microscope using the 4x and 10x objectives. This appear to be S. membranifera when compared with images by April Nobile on

Head of Strumigenys taken through Bausch & Lomb dissecting microscope. This appear to be S. membranifera when compared with images by April Nobile on This species is documented for California.

10. Black Pyramid Ant (Dorymyrmex insanus) On External Link

11. Argentine Ant (Linepithema humile) On External Link

Smallest Ant In Twin Oaks Valley

12. Formicinae: Brachymyrmex patagonicus In Twin Oaks Valley

Rover Ant (cf. Brachymyrmex patagonicus) These ants have a dark brown-black body; they appear lighter in picture due to backlighting and alcohol solution. They were collected on flagstone in my backyard along with mite and springtail. There were also numerous Argentine ants in the area. On 19 September 2018 I collected one in a pitfall trap on bridle path in front of my house.

Feeding time at Wayne's Word: Three naturalized species representing 3 subfamilies of tropical ants sipping honey on a small section of flagstone in my backyard. This makes a grand total of 14 ant species living in my yard. It is amazing what you can find crawling around with a magnifying glass! See Ant Species In My Yard!.

Close-up view of a minute rover ant (Brachymyrmex patagonicus).

Small Pheidole In Twin Oaks Valley

13. Myrmicinae: Pheidole (cf. P. californica) In Twin Oaks Valley

Major worker of Pheiodole californica.
Minute minor worker of big-headed ant (Pheidole) collected in pitfall trap on bridle path in front of my home in Twin Oaks Valley. The common name refers to major workers which I did not find (See left Ant.web image.) According to Phil Ward (UC Davis) it may be P. californica. It belongs to the Pilifera Group and is very close to P. clementensis. A larger species with long legs (P. vistana) is fairly common on the slopes of Owens Peak on the west side of Twin Oaks Valley. Pheidole is one of the largest ant genera with approximately 900 described species worldwide (and an estimated 1500 species)!

  See Pheidole vistana On Owens Peak West Of Twin Oaks Valley   

Another Minute Subterranean Ant In Pitfall Trap

14. Ponerinae: Hypoponera opacior In Twin Oaks Valley
Hypoponera opacior, H. opaciceps & H. inexorata reported from CA by Phil Ward.

Using the AntWiki Key To US Hypoponera it is H. opacior; ID verified by Phil Ward on 24 July 2018.

The subfamily Ponerinae includes some very interesting species, including the sickle-jaw ant (Leptogenys falcigera) in Maui, trap-jaw ant (Odontomachus bauri) in Costa Rica, and Panther Ant (Pachycondyla) from Machu Picchu in the Peruvian Andes.

  See Other Genera In Subfamily Ponerinae On Wayne's Word  

Parasitoid Wasp In Midden Of Forelius mccooki Nest?

This minute wasp was found in the midden of a Forelius mccooki colony on bridle path in front of my home. Could this be a parasitoid wasp? It resembles images of diapriid wasps (subfamily Diapriinae, genus Trichopria) at Parasitoid wasps include some of the smallest insects with the greatest number of species. I always thought beetles had the largest number with 300,000 described species. The parasitoid wasp superfamily Chalcidoidea alone has an estimated 500,000 species! According to BBC-Earth, parasitoid wasps may be the most diverse animal group with 2 million species. Diapriinae wasps have been found associated with ant nests in Argentina according to Psyche: A Journal of Entomology, including the Argentine ant (Linepithema humile).

Two additional wasp species in Forelius mccooki midden. Left: A chalcid wasp in the family Chalcididae. Note the enlarged leg segments (femora). Right: Fig wasp Pleistodontes imperialis (family Agaonidae), symbiotic pollinator of rustyleaf fig (Ficus rubiginosa) that grows across the street from bridle path. The chalcid wasp may be a parasitoid species. I found a dozen individuals in the midden sample so they may be parasitic on this Forelius mccooki colony.

  Pollination Of The Rustyleaf Fig By Its Symbiotic Fig Wasp Pleistodontes imperialis   
  See Heads Of Snakefly (Raphidioptera--Raphidiidae) Found In Pitfall Trap On Bridle Path   

Other Species Found Along the Lower Slopes of Merriam
Mountains and Owens Peak That Border Twin Oaks Valley

15. Formicinae: Myrmecocystus In Merriam Mtns

Honey Pot Ant (Probably Myrmecocystus wheeleri)

  More Images Of Myrmecocystus In The Merriam Mtns  
Myrmecocystus mexicanus near Holbrook, Arizona

Owens Peak West Of Twin Oaks Valley

16. Formicinae: Myrmecocystus testaceus

I recently found another ant species in my traps on Owens Peak. I am reasonably certain it is a large-eyed, nocturnal species of honeypot ant (Myrmecocystus testaceus). It clearly belongs to the subfamily Formicidae with one petiole node and an acidopore. In addition, it has long maxillary palps typical of Myrmecocystus. I also collected this species in a trap at Daley Ranch. This makes a grand total of 16 species for Owens Peak!

Ant Species 17 - 20 On External Links

17. Red Harvester Ant (Pogonomyrmex subnitidus) On External Link

18. Black Harvester Ant (Veromessor andrei) On External Link
Note: Also Listed As Messor andrei In Some References

19. Orange Desert Ant (Forelius pruinosus) On External Link

20. Big-Headed Ant (Pheidole vistana) On External Link

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