How to identify Pheidole megacephala

Image from Australian Department of Agriculture and Food
website, authored by Marc Widmer

Identifying whether or not the ants you have are P. megacephala is important.

STEP 1. Size the ants

The first step is to size the ants.

P. megacephala is a small ant.

The minor workers are around 2 mm in length, and even the major workers aren't more than 4 mm in length.

STEP 2. Identity as Pheidole

The second step is to separate them out from other tiny ants.

Most Pheidole have two worker types, although the major workers only make up a fraction of the work force. In P. megacephala, majors on average are around 20% of the total. If you see ants that have a strictly dimorphic worker force, then it probably is a Pheidole. In addition, Pheidole also do not sting, unlike the Solenopsis fire ants.

Photograph by R.H. Scheffrahn, University of Florida

Step 3. Identify as P. megacephala

The third step is to separate P. megacephala out from other Pheidole.

Unfortunately, doing this without a magnifier or handheld microscope is somewhat difficult.

P. megacephala antennae are 12-segmented, with a 3-segmented club.

Look at one of the workers from the side. You should see a two segmented waist that connects the thorax (mesosoma) of the ant to its abdomen.

Photo modified from April Nobile @Antweb.org

The postpetiole (the second part of the "waist") of P. megacephala is enlarged and is significantly longer than it is broad, and has convex protrusions above and below, when viewed from the side. The bottom protrusion comes first (closer to the mesosoma or thorax, blue arrow below), then the top protrusion comes next (closer to the abdomen, red arrow below). It is bell-shaped as well when viewed from above.

Modified from antweb.org

This separates out P. megacephala from all other Pheidole, except for (1) two relatively rare species in the Costa Rican rainforest (which can be separated out by the head shapes of the major workers) and (2) if you are in Madagascar and surrounding islands, or areas where this species is thought to originate (Southern Africa). In this case, such features are also present in P. decepticon and P. megatron, both of which are not invasive.

The major worker or soldier of the species also has a couple of features to look for in addition to the unique post-petiole shape.

Image from Antweb.org

The head of the major worker is heart shaped, as well as relatively smooth, shiny and hairless on its top surface, and the thorax has a single large "hump" when seen from the side, without any second protrusion behind it.

Image modified from Antweb.org (Shannon Hartman)

Two other behavioral features of the ant may help in its identification.

First, P. megacephala tends to have distinct foraging trails, unlike many Pheidole.

The entrances of their nest also tend to be surrounded by displaced soil, and unlike many Pheidole, they usually have multiple nest entrances instead of one single entrance.

Photograph by R.H. Scheffrahn, University of Florida

Finally, unlike many Pheidole, this species tends to have very populous nests, and their foraging trails tend to have many workers streaming back and forth (although during the heat of the day, it's likely you will see only individual foragers).