aaron567's Journal

I made this key as a more straightforward and dichotomous version of my previous journal post while still retaining more simple vocabulary and refraining from the usage of highly obscure latin-rooted descriptor terms that tend to be abundant in other ant keys. By "small Pheidole" I am referring to species with minor workers generally under 2.5 millimeters in length. Unlike in the last post, I have included P. megacephala here because it probably meets or comes close to meeting that requirement. This key is made for Florida but should work fine for Mississippi, Alabama, Georgia, and the Carolinas. I have excluded flavens and floridana from this key.

1)
Minor worker yellow, orange, or reddish brown; may have darker gaster → (2)
Minor worker black, black-iridescent, brownish, or brown-bicolored → (8)

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2)
All castes shiny and yellow/orange → (3)
Minor worker matte or non-shining; color yellow to reddish brown → (4)

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3)
Major worker and gyne with truncated (flattened front) head; minor worker lacking propodeal spines; restricted to small areas of north Florida, particularly around Tallahassee and the AL/FL/GA tri-state region → P. lamia
All castes have fairly normal shape and proportions for Pheidole; uncommon species in north or central Florida, inhabits open ground in residential lawns or natural areas → P. tysoni

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4)
Postpetiole of major worker about the same width as petiole or only scarcely wider → (5)
Postpetiole of major worker twice or nearly twice the width of petiole → (6)

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5)
All castes except males red with dark gaster; head of major worker and gyne is fairly elongate with pointed posterior lobes and criss-crossing striae on upper portion; very common species in urban areas across FL, but rare or absent in natural areas; alates attracted to lights after dusk → P. parva
All castes variable in color (gyne almost always fully dark brown to blackish); head of major worker and gyne is not as elongate and has more rounded lobes and only vertical striae; very common species in urban areas and wetter natural habitats across FL; alates attracted to lights at dawn → P. navigans

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6)
Major worker unusually large, clearly more than twice the total length of minor worker; minor worker with proportionally larger eyes than other Florida Pheidole; nests in open sand in natural areas of northeast and north-central Florida → P. carrolli
Major worker typical in size for Pheidole → (7)

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7)
Minor worker and major worker with proportionally smaller eyes than other Florida Pheidole; nests in leaf litter or sometimes underneath wood in natural or semi-disturbed wooded areas throughout FL; gyne very small (total length <5 mm) and concolorous or nearly concolorous orange with a proportionally large head; alates attracted to lights at dawn → P. dentigula
Workers with proportionally typical eyes; posterior region of the head of the major worker completely smooth and shiny, lacking any striae; gyne larger (total length >5 mm); major worker and gyne often with a pair of lighter-colored semi-circles at base of gaster; common species in natural and sometimes disturbed areas, usually nesting in open sand; alates attracted to lights at dawn → P. bilimeki

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8)
Minor worker fully black or black-iridescent, either shiny or matte/nonshining → (9)
Minor worker brownish or brown-bicolored, always shiny → (13)

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9)
Minor worker generally matte or non-shining; major worker and gyne with red or reddish-brown head and mesosoma; nests in open sand → (10)
Minor worker shiny → (11)

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10)
Major worker with comically large head even for Pheidole; minor worker with unusually large eyes that pop out quite noticeably from the sides of the head; very faint blueish iridescence is sometimes seen in photos of the minor worker; found in natural sandhill or scrubby areas throughout FL → P. littoralis
Head of major worker typical for small Florida Pheidole; minor worker with typical eye size for Pheidole; minor worker with strong blueish or purpleish iridescence that can be seen with the naked eye; common species found in natural or semi-disturbed open wooded areas in north and central FL; alates attracted to lights after dusk → P. metallescens

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11)
Minor worker with strong blueish or purplish iridescence that can be seen with the naked eye → P. metallescens
Minor worker lacking iridescence entirely → (12)

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12)
Head of major worker and gyne very elongate in a way that is unusual for Pheidole, especially in the gyne; currently restricted to urban Miami area but expected to spread; alates attracted to lights at dawn → P. subarmata
Head of major worker and gyne not unusually elongate; found in natural sandhill or scrubby areas throughout FL; alates attracted to lights after dusk → P. adrianoi

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13)
Mesosoma of minor worker generally the same color as the head, with gaster sometimes darker; head of major worker and gyne very elongate in a way that is unusual for Pheidole, especially in the gyne; currently restricted to urban Miami area but expected to spread; alates attracted to lights at dawn → P. subarmata
Mesosoma of minor worker lighter in color than head and gaster (except in oldest workers) → (14)

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14)
Forms large supercolonies with dozens to hundreds of queens; minor worker up close has body shape and proportions more akin to larger Pheidole species (more gracile); found in urban or residential areas of peninsular (especially south) Florida; gyne dark brown or blackish in color; nuptial flights take place at dawn → P. megacephala
Doesn’t form supercolonies, has one queen per colony; minor worker has typical proportions for small Florida Pheidole; mostly found in open disturbed and semi-disturbed areas of north Florida (especially abundant in panhandle); gyne orangey brown to dark brown, sometimes with darker gaster; nuptial flights take place at dusk with alates attracted to lights → P. bicarinata

Many of the small Pheidole species, particularly those in the flavens-group, can appear difficult to identify. Here are the steps I go through to identify them.

First, we will look at the species with shiny minor workers.

Shiny minors:
P. adrianoi --> Found only in less-disturbed sand scrub and sandhill in Florida and adjacent states.
P. bicarinata --> Variety of habitats, loves disturbed sites. In Florida, restricted to the panhandle and northernmost FL. Generally not found in sandhill or scrub. Varies from dark brown to yellowish.
P. davisi --> Found in sandy pine barrens from Georgia to New York.
P. metallescens --> Common in sandy sites across the southeast. Minors have a unique blue/purple iridescence that makes them easily recognizable. Majors are small and reddish brown.
P. subarmata --> Restricted to urban Miami, blackish or brownish in color. Head of the major is elongated.
P. tysoni --> All over the southeast minus the southern half of Florida. Enjoys disturbed habitat but can be cryptic.

P. adrianoi vs P. davisi:
Almost identical in morphology. Use location to determine species. Majors of these species have conspicuously rounded heads.

P. bicarinata vs tysoni:
Lighter-colored bicarinata can look quite similar to tysoni. Both the majors and minors of tysoni have slightly smaller eyes, and the majors have a more elongated head than bicarinata. The behavior of bicarinata is less cryptic and you are much more likely to see majors foraging above ground than with tysoni.

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Now we will look at the more tricky group of species, the ones with non-shining minors:

P. bilimeki --> Widespread in southeast & can nest in the ground or in association with rotting wood.
P. dentigula --> Widespread in southeast & nests in rotting wood.
P. flavens --> Rare & restricted to south FL.
P. floridana --> Restricted to southeast FL, could be synonymous with bilimeki.
P. littoralis --> Found only in sandhill and sand scrub in Florida and adjacent states. Black in color.
P. navigans --> Widespread in southeast, wide variety of habitats.
P. parva --> Prevelant mostly in urban/suburban parts of Florida.

We can split all of these species (excluding littoralis) into two groups: those with a wide postpetiole and those with a narrow postpetiole. This character shows up in both minors and majors but is more obvious in majors. For example:

Postpetiole obviously wider than petiole:
P. bilimeki --> Back portion of the major's head is shiny and lacks sculpture.
P. dentigula --> Back of major's head not shiny. The lobes at the back of the head of the major come to more sharpened points, similar to P. parva. Minors typically have a yellow gaster.
P. floridana --> Almost identical to bilimeki but supposedly with a shinier gaster and postpetiole. Only known from the Miami area and the taxonomic status is unclear. P. floridana could just be an introduced tropical population of P. bilimeki.

Postpetiole about the same width or only barely wider than petiole:
P. flavens --> Rare and only known from south Florida. Very similar to navigans, but head of the major is less shiny and antennal scrobes are more shallow.
P. navigans --> Widespread in the southeast and found in a variety of habitats.
P. parva --> Prevelant mostly in urban/suburban parts of Florida.

P. navigans vs P. parva:
Minors are difficult to tell apart, but parva is often more strongly bicolored than navigans. The best way to separate these species are by the major workers; the major of parva has a more elongated head with sharper lobes and is less shiny than the major of navigans. There are also irregular ridges present on the posterior of the head of parva, unlike in navigans.

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Separating P. adrianoi from P. littoralis

Let's look at these two species by themselves since they are both have small, black minors that are only found in sand scrub and sandhill and can be present in the same areas.

Minors can be very difficult to tell apart unless you are looking at them side-by-side. In northwest Florida, P. adrianoi minors are noticeably smaller than P. littoralis minors, but this is apparently not applicable everywhere. Minors of P. adrianoi are very shiny and are lacking in sculpturing, and their heads are slightly more rounded than those of P. littoralis. P. littoralis minors are more dull in texture and have larger eyes that bulge farther from the sides of the head.

But the best way to reliably tell these species apart is by their majors. Unlike the minors, the majors are completely different and unable to be mistaken. The major of littoralis is very large compared to the minor (unusually large, even for Pheidole) and has non-shining, brick-red head. The proportions of the major of adrianoi are much more typical for small Pheidole, and is fully shining. It is apparently more common for P. adrianoi majors to venture outside the nest than for P. littoralis.