From Holocron - Star Wars Combine
|Language||Pak Pak |
|Average Height||1.6 to 2 meters |
|Skin color||Greenish-gray |
|Hair color||None |
|Known Members||List of known Neimoidians|
Biology and appearance
If there's money to be had, a Neimoidian will be nearby. So says a common spacer stereotype, justified by the species' reputation for excelling at business. This race of aliens resembles the Duros in many physical respects, having descended from pure Duros stock when a group of colonists settled on Neimoidia some 25,000 years ago.
They have smooth, greenish skin and large, red eyes, although the Neimoidian eye has a pupil which splits it horizontally. They also have a more developed cranium, which is studded with small knobs and bumps. Their mouths are down-turned, giving them a perpetual frown. The Neimoidian life-cycle has contributed much to their cut-throat business acumen; they live in communal hives from the time of their birth to the age of seven. In those seven years of grub-hood they are given limited access to food sources. The grubs then compete for food, and many young die if they are too weak to fend for themselves. This helps weed out the weak individuals at a very early age, as those grubs which can't find food or steal it quickly die. This method of raising their young instills tremendous greed into the young Neimoidians, but it also forces them to become organizational.
Their sense of smell came from glands under their eyes. These genetic differences were attributed to the distinct features of their homeworld, Neimoidia - including its gravity, which was heavier than Duro. 
Neimoidian skin often took on a mottled look if the being was too self-indulgent or often prone to great stress. A Neimoidian's lung pods would expand and contract convulsively under great stress, leading to an old saying characterizing Neimoidians as the only sentient species with an entire organ devoted to worrying. Nauseated Neimoidian's skin turned pink. The Neimoidians have five fingers and two clawlike toes. 
Neimoidians were born in a larval state called a "grub" form. Although hive-mothers had cloacas, the grubs were born live and not from eggs. 
It is well-known that Neimoidians were notorious disease carriers. At several times in the past, Neimoidia had been quarantined and forbidden to travelers. Upon death, Neimoidian bodies would desiccate rapidly if not immediately buried or burned. The corpse's face would elongate, and the brain sac would shrivel into a series of tiny pods behind the head. It was this terrifying image of death, coupled with the Geonosian physique, that inspired the appearance of some of the battle droids. 
Society and culture
Since most able Neimoidians left their homeworld in search of a better life, the general population of Neimoidia was made up of the weakest of the Neimoidian people. In general, the Neimoidians are entrepreneurial, but are also lazy cowards. They have developed one of the most advanced droid technologies in the galaxy, and use automatons for everything. They developed droid chairs, droid starships, and entire droid armies. They are also very conscious of rank and position, and use all methods of clothing to describe their status. Elaborate headdresses; the cut, color, and texture of the cloth; and the collars and trim of their clothing all have specific indications of rank and position. Though they call Neimoidia home, Neimoidians can trace their ancestry to the ancient Duros spacefaring culture. The two species share a striking similarity in appearance, but their personalities could not be more distant. While the Duros are a gregarious, expressive and adventurous lot, the Neimoidians seal themselves away from others, preferring to let droids do their talking. Neimoidians place great value on wealth, and dress to display their riches accordingly. High-ranking officials dress in ornate and lavish gowns, towering headpieces, and the elite even travel about in inconvenient yet expensive conveyances called mechno-chairs.
Neimoidians spoke either heavily-accented Basic, or a distinct non-verbal form of communication referred to as Pak Pak. Pak Pak was comprised mostly of guttural grunts and croaks, and non-Neimoidians found it rather difficult to comprehend. Many low-level worker drones were kept malnourished so as to never reach full mental maturity. Combined with the planet's natural unpleasantness, it was usual for Neimoidians to choose not to return home unless absolutely necessary.
As adults, Neimoidians had a reputation of being skilled in matters of business and were well known for their leadership of the Trade Federation. Unfortunately, Neimoidians were stereotyped by other species as greedy, fearful of death, lazy, and corrupt. This is evident by the use of droids for almost everything. It was often said that one of the most difficult concepts for a Neimoidian to understand was loyalty. It was also said that no one would ever see a Neimoidian without their hat, unless they were dead. 
Twenty five thousand years ago, a Duros colony was established on Neimoidia under the leadership of Chla C'cHaan. Due to the distinct features of Neimoidia, including a gravity which was greater than Duro, the Duros colonists became a separate species from their genetic cousins, thus starting the Neimoidian species. During an expansionist period in the Galactic Republic era, the Neimoidians colonized several nearby worlds. The wealthiest and most resource-rich colony worlds were known as "purse worlds", that also served as administrative posts and ruled their own set of colonies. Notable purse worlds included Cato Neimoidia, Deko Neimoidia, and Koru Neimoidia.
Three hundred and fifty years ago, the Neimoidians helped establish the Trade Federation, an association of business and trade groups which grew to dominate entire star systems. 
References:  - http://starwars.wikia.com/wiki/Nemoidian