Lyleks were a species of sizable insectoid predators that were indigenous to the equatorial forest on the planet Ryloth. Sporting spiked pincers, powerful mandibles accompanied by a pair of tentacles, lyleks were considered the most dangerous lifeform on Ryloth, even more so than the predatory gutkurrs. Their bodies were protected by ridged, spiked carapaces capable of deflecting blaster bolts. While lyleks congregated in large groups, the larger members of these groups were known to dismember the smaller ones. These groups, or hordes, were governed by a lylek queen, and their complex underground nests could span areas as large as 15 square kilometers. They used hisses, clicks, and chittering sounds to communicate. Their carapaces provided significant protection, capable of withstanding heavy blaster fire, but a well-placed shot to the head could kill them.
Around 228 BBY, the Evereni Marchion Ro had personally engaged in combat against lyleks, fighting them with his bare hands.
During their mission to Ryloth, Emperor Sheev Palpatine and Darth Vader were attacked by a lylek swarm after their Star Destroyer, the Perilous, was brought down by members of the Free Ryloth Movement. The two Sith Lords engaged in a running fight against hundreds of these creatures, eventually being driven into the swarm's central hive. Inside, they eliminated the enormous lylek queen and proceeded to slaughter the hundreds of remaining drones.
The first mention of the lyleks of Ryloth was in the 1998 reference book The Essential Guide to Planets and Moons, authored by Daniel Wallace. The creature's name was chosen as a tribute to Wallace's wife, Kelly.