Kikaichū

are a species of small, beetle-like insects that are bred and utilized exclusively by the Aburame clan, forming the basis for all of their unique techniques. All members of the Aburame clan actually live in symbiosis with the kikaichū through the practice of a Hiden Jutsu; the Destruction Bug Host Technique: The Aburame clan, shortly after birth, allows the kikaichū to nest and breed inside the their bodies and feed off of their Chakra, and, in return, through this practice, the host ninja receives the life-long ability to control and command the bugs, using them as their primary fighting technique.

The most common use of the kikachū in combat is to ambush an opponent and drain them of their chakra before they notice the bugs at work. This process can leave the victim with so little chakra that unable to move or fight back. Other uses include simply tracking down a target, serving as a a protective shield and as a prison to hold and detain a target in place. The kikaichū can fly, and they will typically move in swarms when on the attack, or in smaller numbers when practicing stealth. A female bug can be left on a target and then they can be tracked by smell, or scout bugs can be sent out and return to tell the host information about the area. Thanks to the kikachū, Aburame clan members are experts in communication and espionage, due to their ability to communicate with the insects, stealth because the kikaichū make no noise or motion during combat, as well as in search-and-seizure missions.

Usually, since the kikaichū only have a lifespan of a few hours, they are always breeding safe within their host, maintaining their numbers. Because of their short lifespans, the kikaichū are easily expendable in combat. If large numbers of the kikaichū should be wiped out, then the bug-user can utilize Secret Technique: Insect Cocoon, a technique which can be used to rapidly breed a whole new generation of the kikachū, repopulating their numbers.

Since the kikachū only have a lifespan of a few hours, their life cycle ensures that there will always be females with eggs. Any variations that prove useful to the individual bug, and consequently the bug-user, in combat such as immunities will be passed on to the next generation, which can then be cultivated for their success against dangerous opponents in combat. The immunities gained from the kikachū can be used as a defense mechanism; by exerting chakra, the original source of the immunities can be rendered useless or can be destroyed on contact. For example, when the kikachū gained immunities to Guren's unique Crystal Release, they were able to resist being crystallized, and were able to shatter her techniques on contact.

Highlighted during the 'Kurama clan' arc, another of the kikaichū's notable atributes is their immunity to genjutsu: Lacking higher brain functions, the kikaichū's actions are governed almost entirely by their five powerful senses and simpler nervous systems. Because of this, they are unaffected by genjutsu--which are designed to affect more complex nervous systems along with the higher brain functions of humans. Unlike humans and other animals, the kikachū do not even notice genjutsu. This immunity to genjutsu is also extended to the recipients of the Destruction Bug Host Technique, allowing the bug-user to detect genjutsu, and to be able to function against genjutsu-users at the same capacity without impaired judgement.

Trivia

 * Kikai, when written as 奇怪, means "strange", or "mysterious".