Grubs are type of worm or millipede that can be found throughout the Southern Continent, as well as parts of the Northern Continent. Also called Sandworms, they are known for their consumption of Thread and for their beneficial effects on plant life.
Grubs were genetically engineered by Ted Tubberman to protect fields and crops by tunneling underground and devouring any Thread that has burrowed. Forgotten over time, grubs flourished in the Southern Continent, preventing the plant and animal life there from being destroyed by thread. Some grubs appeared in the Northern Continent, but their existence was known only to the Farmercraft. Farmercraft records indicated that the grubs should be watched for, but a loss of context led generations of Farmers to destroy them as parasites.
The grubs ability to devour thread would be rediscovered by F'lar, Weyrleader of Benden Weyr, who witnessed the grubs activity while helping to fly a premature fall. After a series of tests, F'lar realized that the grubs ability to devour thread could serve as a means of protection. Eventually, he brought in Masterfarmer Andemon to assist, who realized that the grubs were the pests he had be trying to eliminate. After performing his own tests, he came to realize that his craft had misinterpreted old records.
F'lar would begin a long term project to seed grubs in the most thread vulnerable areas, such as the forests of Lemos, and worked to convince the Lord Holders of their value, which proved difficult. However, a demonstration of the grubs abilities during falls not flown by dragons was able to convince many.
Grubs are a genetically engineered species that serves as a line of defense against Thread. They reproduce by means of larval sacks which infest fields. Due to a misinterpretation of records, members of the Farmercraft attempted to eradicate them using fire, but Grubs proved to be difficult. It can be difficult to find grubs, as they typically only surface during Threadfalls. In areas inhabited by grubs, plant life will flourish due to grubs aerating the soil and preventing Thread infestations. Minor wilting of plants has been known to occur soon after grubs appear, which helped fuel their negative reputation, but most plants will recover after watering.