Trill symbiont A Trill symbiont was a sentient vermiform lifeform from the planet . They primarily lived symbiotically inside host s of the humanoid species Trill , also native to the planet . Through the experience gained from multiple hosts , many symbionts gained distinguished reputations from other species as Trill . Also as a result , they were long - lived compared to most humanoid species , and could easily live beyond 550 years . Physiology . The Trill symbionts were teardrop - shaped , asexual , and could swim in their natural pools , such as the Caves of Mak ' ala . The symbionts communicated with each other via electrical impulses transmitted through milky water that they inhabited . They also had a limited form of communication with certain Trill while not joined . ( ) A Trill symbiont joined with a new host through a surgical procedure in which it is placed in the abdomen , where it developed a connection through the narrow part of its body to the host ' s body . Once a symbiont was joined for over ninety - three hours , the symbiont became dependent on its Trill host and vice versa ; the Trill would die within hours without a symbiont , and the symbiont could not return to the Caves of Mak ' ala ( if joined for the first time ) nor survive a significant period of time outside of a host . ( ) After and during joining , symbionts took with them all of the memories of their previous Trill hosts so , upon joining , the new Trill host gained those memories . The brains of the symbiont and host were able to communicate , and , indeed , did not function separately . Analyzing the brain wave patterns of the symbiont separately from the host was possible , and , to a degree , the symbiont ' s patterns do not change significantly from host to host . ( ) Although Human s could be used as a host to a symbiont , the symbiont could not remain in their bodies for long without physically harming the Human host . ( ) A symbiont could survive normally in a partly Trill host , however . ( ) Society . The Trill symbionts relied on the Trill to survive through hosts . The Symbiosis Commission oversaw the joining of the vermiform symbionts and humanoid Trills . Through the Commission , the symbionts were cared for by Trill s and implanted only into Trill that had undergone a rigorous testing process , ensuring the new host had a high intelligence , balanced personality , and would not reject the symbiont . ( ) In the 24th century , about 500 symbionts became available for joining , each year , compared to approximately 5 , 000 Trill becoming initiates per annum . The relatively low quantity of symbionts resulted in Trill society hiding from their general populace the fact that virtually 50 % of the population was suitable for joining , and the general belief in the 24th century was consequently that only one in every 1 , 000 Trills was suitable for joining . ( ) Until the mid - 24th century , it was not widely known that Trill were actually a joined species , as it was considered a private matter . New hosts often had to produce false stories as to why he or she had certain memories of previous hosts . This true nature became known to the in 2367 , when Ambassador Odan ' s male host at the time died , forcing the Commission to send a new host , Kareel , to the for joining . Beverly Crusher became the first Starfleet doctor to learn and perform the process . ( ) Appendices . Background information . For , Michael Westmore based the design of the symbiont on a caterpillar ' s body attached to the head of an octopus . ( " Michael Westmore ' s Aliens : Season Two " , DS9 Season 2 DVD , special feature ) A few convolutions were added to make the appliance look as if the symbiont had lots of brain matter . An air bladder was inserted into the symbiont ' s head and pulsated to give the impression that the symbiont was alive . The head was also colorized with a fluorescent paint , making it glow when exposed to black light during a surgery scene . ( " " , p . 117 ) For the second appearance of a symbiont , in pilot episode , Michael Westmore changed the design significantly . The symbiont was " still in a similar vein shape - wise , " he stated , though the revised version was smaller than its predecessor . ( ) " " One [ reason for changing the symbiont ] was to give it more of a streamlined look [ . . . ] The way this [ altered version ] was designed , it was almost like a roundish type of a triangle , with these little feelers that would bend back , " " explained Westmore . " " And by putting a lot of KY Jelly on it whenever we would do the effects , it would slide a lot easier . " " ( " Michael Westmore ' s Aliens : Season Two " , DS9 Season 2 DVD , special feature ) The series bible of " Star Trek : Deep Space Nine " stated , " " The symbiont is an invertebrate , androgynous lifeform that lives within the host . It looks like a short , fat snake . Many centuries ago , the symbionts lived underground [ . . . ] [ until joining with the hosts ] due to an environmental disaster . " " In the first draft script of , a hypothetical evolutionary link was made between Trill symbionts and tribble s , as some xenobiologists had apparently theorized that symbionts were evolved from tribbles . Jadzia Dax consequently referred to the symbiont inside herself as " a very smart Tribble . " According to " " ( p . 33 ) , the existence of the symbionts was not widely known until 2367 ( the year in which " The Host " is set ) .