Polyrhachis sokolova

This is the only species of Polyrhachis known to nest in marine and estuarine mud of the intertidal zone. Its nests are mound-like, with a small opening at the top, and are completely submerged at each high tide. Distribution is limited to the tidal mudflats of coastal mangrove forests. (Kohout 1988) (Robson 2010)

Distribution based on Regional Taxon Lists
Australasian Region: Australia, New Caledonia. Indo-Australian Region: New Guinea.

Polyrhachis sokolova occurs along the Australian coastline from Torres Strait to as far south as Gladstone in central Queensland (Kohout 1988). It is a quite common species that also occurs beyond the Australian mainland, with records from the Aru Islands, the southern coast of Papua and New Caledonia (Kohout, 2013).

Biology
From Narendra et al. (2013) P. sokolova lives in mudflat habitats and are probably one of the only intertidal ants in the world, making nests at the base of trees in the mangroves. They forage individually, exploiting the dead organisms that are washed up. Their nests and foraging sites get inundated during high tides. Hence to get to their nest, they swim with a kind of freestyle, tucking the back two sets of legs behind and using the front legs as a human would to propel forward. They are about three times faster on water than their walking speed on land. But they mostly forage on ground and swim only when there is no option.

Although P. sokolova ants are very good swimmers, they like a dry home and have developed some tricks to keep their homes watertight. The architecture of the nest is very unique: the entrance doesn't open up directly into large chambers as it does in most other ants nests, they have S shaped curved patterns which create enough surface tension to block the water from coming into the nest.

Workers are active during low tides at both day and night and thus experience a wide range of light intensities, and this is reflected in the structure of their compound eyes.

Nomenclature

 *  sokolova. Polyrhachis sokolova Forel, 1902h: 522 (w.) AUSTRALIA. Combination in P. (Hagiomyrma): Emery, 1925b: 185; in P. (Chariomyrma): Kohout, 2013: 491. Senior synonym of degener: Kohout, 1988c: 436.
 * degener. Polyrhachis sokolova var. degener Forel, 1910b: 84 (w.) AUSTRALIA. Combination in P. (Hagiomyrma): Emery, 1925b: 185. Junior synonym of sokolova: Kohout, 1988c: 436.

Description
Kohout (2113): When describing Polyrhachis sokolova, Forel indicated that it belonged to the ammon-group and, consequently, Emery (1925) and all subsequent authors treated it as a member of the subgenus Hagiomyrma. However, P. sokolova features laminate pronotal margins with acutely spinose humeri, a character common to species of the subgenus Chariomyrma Forel. In fact, small specimens of P. sokolova (‘var. degener’) are remarkably similar to Polyrhachis constricta, described by Emery from Australia in 1897, and subsequently placed by him in the subgenus Chariomyrma (Emery 1925: 186).

Specimens from the Northern Territory differ in several characters from those from Queensland and were earlier considered a separate, undescribed species (see Kohout 1988: 436; Nielsen 1997: 16). However, subsequent examination and comparison of Northern Territory specimens with others from throughout the range of P. sokolova, has shown no taxonomically significant variability to justify their separate specific status. At many localities in the Northern Territory, P. sokolova is sympatric with Polyrhachis constricta and their undeniable similarity resulted in Andersen (2000) correctly listing both species under the subgenus Chariomyrma.