Identifying Small Southeastern Pheidole species

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.

Julkaistu kesäkuu 21, 2022 06:04 IP. käyttäjältä aaron567 aaron567

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Nice writeup Aaron!

Lähettänyt heathrichter noin 2 vuotta sitten

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