Tyranids - Reconnaissance: The earliest stages of a Tyranid infestation of a new world are best characterised by their subtlety. At this stage, the xenos evaluate the planet's viability for attack and begin to infect the native life forms.The three Tyranid species most active during this stage are Vanguard Drone Ships, Lictors, and Genestealers. These bioforms share two critical characteristics for identifying new target planets and performing infiltrations: stealth and independence from the Hive Mind. All of the organisms involved have physiological abilities that are focused upon concealment. These talents are exploited to the utmost, so that they can initially observe the native environment safely. As there are often a very limited number of Tyranids involved at this stage, these specimens exhibit an uncharacteristic degree of self-preservation.The creatures are clearly aware that they must survive and propagate before the invasion may proceed. These specimens are distinctive from most of the Tyranid horrors in that they are also capable of stable independent action. The vast majority of known Tyranid organisms are incapable of coordinated activity when separated from the psychic emanations of the Hive Mind. As these creatures must be capable of acting when light-years distant from the swarm, they manifest a greater degree of intelligence, control and animal cunning than would otherwise be expected. This becomes most evident in the often unexpected subtlety of their plans.Vanguard Drone Ships depend upon speed, their relatively small size, and their reduced psychic and propulsion signatures to enable them to quietly scout out new star systems. In many cases, a Vanguard Drone Ship will deposit a portion of its living cargo onto the surface of a likely prey planet, and then quickly leave the system to scout out targets in other systems.As their time in the system is both brief and stealthy, Imperial agencies may remain completely unaware of the foreboding intrusion. In those cases when a drone ship is identified, it must immediately be considered the highest priority target in the system, as destroying it before it can deploy its cargo may significantly delay any Tyranid intrusion.Lictors are masters of unseen reconnaissance. After insertion on a target world from a drone ship, these xenos immediately begin scouting the wilds of the newly identified planet. Using their Feeder Tendrils, they analyse the atmosphere, mineral availability, and the phenotypic and genetic characteristics of all native life forms. In addition, these fierce predators also target isolated animals and even sapients, if any exist, to absorb their memories as they devour them.This information is compiled and sent back to the Hive Mind as soon as a psychic synaptic node within range is available. Any Lictor that can be eliminated prior to the start of a full Tyranid invasion can substantially slow the attack, as the invading xenos are less optimised for the planet's ecosystem.Genestealers are the most insidious of these early invaders. As they scout out the target planet, they also infect the planet's fauna with Tyranid genetic material. The corruption of the planet's native gene-code eventually results in hybrid native-Tyranid creatures, particularly among any population of intelligent beings like Humans, that are subject to the will of a Broodlord or other representative of the Tyranid Hive Mind.It is also believed that Genestealers may use their cunning and stealth to infiltrate planets without the aid of a drone ship. Specimens have been found on abandoned space hulks and hidden among the cargo holds of Warp-capable Imperial vessels. These creatures, once discovered, must be eliminated with extreme prejudice, before they establish a breeding nest and a community of dedicated hybrid organisms that form the nucleus of a Genestealer Cult. Once Tyranid species have established a toehold on a planet, their strategy soon changes.Successful integration of the planet's wildlife triggers these infiltrators to emit a psychic call to the swarm. This call draws a fleet of vessels, including a Hive Ship, to the system. The arrival of the Hive Ship and its escorts heralds the next phase of the invasion.