PREDATORY NEMATODES 
(Steinernema sp and Heterorhabditis sp)
 These predatory roundworms provide effective control of fungus gnats, thrips pre-pupa, root aphids, black vine and  root weevils, and over 200 other species of insects. Nematodes attack soil pests  by entering through their body openings and releasing bacterium toxic to the host. Reproduction inside the dead insect results in a new generation of nematodes that disperse to find fresh hosts.
These nematodes are 100% safe for people, pets, & plants. They are perhaps one of the most effective and broad spectrum biological controls available on the market today. They work against a huge range of insects - any with a soil based life stage are susceptible. 
Each jar contains tens of thousands of nematodes, which can be added to multiple terrariums or planters by simply adding dechlorinated water to the jar and pouring the resulting slurry in as needed. 
Rate:  2 applications of 10m2 (100ft2).  If you are trying to control fungus gnats separate the applications by two weeks, this will insure optimal results.