Ant Twin Oaks Valley

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Ants Of Twin Oaks Valley
© W.P. Armstrong 23 August 2017
      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.

  1. Cardiocondyla mauritanica Found In Forelius mccooki Midden
  2. Minute Undetermined Solenopsis (Similar To S. tennessensis      
  3. Fire Ant (Solenopsis xyloni) Found On Bridle Path
  4. Forelius mccooki Active Nests On Bridle Path
  5. Fungus Farming Ant (Cyphomyrmex wheeleri
  6. Miniature Trap-Jaw Ant (Strumigenys lousianae)
  7. Miniature Trap-Jaw Ant (Strumigenys undetermined)
  8. A 3rd Species of Strumigenys: Possibly S. membranifera
  9. Honeypot Ant (cf. Myrmecocystus wheeleri) Merriam Mtns
  10. Honeypot Ant (cf. Myrmecocystus testaceus) Owens Peak

    Other Species In Twin Oaks Valley Also On Owens Peak

  11. Black Pyramid Ant (Dorymyrmex insanus) Bridle Path
  12. Argentine Ant (Linepithema humilis) Bridle Path & Home
  13. Harvester Ant (Pogonomyrmex subnitidus) Merriam Mtns

  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 mauritanica

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

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.

A small Myrmicine ant from South Escondido, a few miles from entrance road to Daley Ranch. Above image 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). Apparently they don't always get along because I found two deceased Cardiocondyla in a Forelius mccooki midden sample from nearby Twin Oaks Valley!

2. Myrmicinae: Solenopsis undetermined (resembles AntWiki images of Solenopsis 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. 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.

4. 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 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.

5. 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  

6. 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)!

7. Myrmicinae: Undetermined Strumigenys species

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 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 approacking 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.

8. 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.

Merriam Mtns North Of Owens Peak

9. 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

10. 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!

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