Polybioides raphigastra

Appearance

"P. raphigastra "bodies are composed of mostly dark areas, with lighter areas near the edge of segmented appendages. These dark areas are pale brown with light areas maintaining various shades of yellow.It is hypothesized that autotomy in "P. raphigastra" occurs as a result of the shape and size of their sting barbs. Stings resemble two sharp rods clasped together and tapered off in width closer to the end known as lancets. The external surface of the lancets possess large, well developed barbs through the length of the sting that are arranged in a helicoidal distribution. The inner passage between the two lancets is the canal through which venom travels as it exits the sting. In "P. raphigastra", this otherwise smooth median margin contains a tooth-like structure and a semicircular incisure. It is proposed that these artifacts, along with the arrangement of the barbs, serve to impede the extraction of stings from the victim.

Distribution

"P. raphigastra" resides primarily in the forests of South East Asia and Indonesia. However, the genus as a whole has a quite peculiar geographical distribution as it contains species residing in the Philippines and equatorial Africa. "P. raphigastra" constructs elaborate nests inside small cavities such as tree trunks. These nests are characterized by vertical combs surrounded by an envelope.

Habitat

"P. raphigastra" resides primarily in the forests of South East Asia and Indonesia. However, the genus as a whole has a quite peculiar geographical distribution as it contains species residing in the Philippines and equatorial Africa. "P. raphigastra" constructs elaborate nests inside small cavities such as tree trunks. These nests are characterized by vertical combs surrounded by an envelope.

Reproduction

The species nests in closed cavities such as caves and hollow trees. When nests are constructed within tree trunks, the trunks are often left entirely intact, with only small crevices giving access to the internal cavities that house the nest. In the trunk cavity, nests hang vertically with the envelope surrounding the nest directly attached to the inside of the cavity. Nests, often ovoidal in shape, may measure approximately 23 cm in length, with maximum diameters of 14.5 x 16 cm. Nests may contain well over ten thousand cells. Nests are egg-shaped and formed of a single, helicoidal comb that winds upon itself eight or nine times in a fashion so that each whorl is partially enclosed by the following one. Nests are entirely composed of very short plant hairs bound together by differing levels of secretion. Nest color is brown to yellowish, and the envelope may be darker than the cells inside. The outer envelope displays crescent-like patterns of colors varying from white to reddish brown. Each whorl on the nest is composed of two parts: a lower aspect constitutes the comb and an upper aspect that forms the envelope; leading to the number of layers of the envelope being roughly equivalent to the number of tiers of whorls. The curved structure, which curls spirally on itself in a series of layers, growing larger and larger may vaguely resemble the shell of a sea snail. Towards the center of each tier, the cells axes point downwards while near the edge of the envelope they are faced almost horizontal. The architecture of "P. raphigastra" nests appear to be unique among the Vespidae, though spiral combs may be found in other species of swarm-founding Ropalidiini and Epiponini. Additionally, its tendency to enwrap and protect previously built structures as it grows is similar to "Agelaia areata.

Defense

It is well known that members of the species respond aggressively to vertebrate animals, with workers often attacking unprovoked at great distances away from the nest, and continuing to pursue their victims for several minutes. Further, these individual workers may effectively tag an enemy and elicit a colony-wide threat response via pheremones located in their venom glands. It is this aggressive response, shared by all members of the genus "Polybioides", that was utilized by the Viet Cong during the Vietnam War. Guerrilla fighters would employ swarms of bees in booby traps intentioned to quick-release these territorial wasps directly nearby enemy troops. The simultaneous aggressive response would leave victims with up to 200 stings, virtually ensuring mortality.The occurrences of sting autotomy in "P. raphigastra" is the first reported for a Ropalidiine species. Autotomy is a common phenomenon in bees and has also been found to occur in several wasp species of the tribes Epiponini and Polistini. Autotomy is the ability of an organism to shed or discard one of its own appendages. In "P. raphigastra," this ability has shown to be a special defensive mechanism against vertebrate predators.It is hypothesized that autotomy in "P. raphigastra" occurs as a result of the shape and size of their sting barbs. Stings resemble two sharp rods clasped together and tapered off in width closer to the end known as lancets. The external surface of the lancets possess large, well developed barbs through the length of the sting that are arranged in a helicoidal distribution. The inner passage between the two lancets is the canal through which venom travels as it exits the sting. In "P. raphigastra", this otherwise smooth median margin contains a tooth-like structure and a semicircular incisure. It is proposed that these artifacts, along with the arrangement of the barbs, serve to impede the extraction of stings from the victim.Venom sacs contain both saturated and unsaturated linear hydrocarbons of a chain length between 11 and 18 carbon atoms. The major components are pentadecane and pentadecene. "P. raphigastra" venom is also known to contain phenol, benzaldehyde, phenylacetaldehyde, naphthalene, indene, limonene and decanal. Additionally, several compounds that have been identified in their venom function as alarm pheromones in other species of social insect.