They'll eat anything and everything that's a similar size to them. Including your springtails.
ahm.. who uses them outside? that's indeed not "thought through".. to say it in a polite way.Fungus gnats are not usually harmful but I do despise them. They get in my coffee, fly up my nose, skittle across my monitors.
Because isopods are my passion these days (and I have a lot of water loving house plants) I just can't seem to get rid of them. The only thing I found that really controlled them well were those yellow sticky traps, but I can only use them in the coldest part of the winter. In the warmer weather my house gets a lot of jumping spiders (probably because I have fungus gnats lol) and I just can't bear the thought of catching any of them on that sticky stuff. Heck, even though I hate the fungus gnats I still feel a bit bad for them too - has to be a horrid death being caught on those sticky traps.
Do be warned though if you use them - those sticky traps catch everything and most smaller critters will be killed or maimed just trying to get them off of the traps. They should probably come with a huge, flashing warning for those who can't think things all the way through. Just go over to Amazon and read the one star reviews from people that were mortified to find geckos, birds and other desirable wildlife stuck to the traps after they took the advice of the sellers to place all over their gardens and yards. I mean, really? Who would do that and NOT realize that the traps will catch anything that touches them. Warning - folks giving reviews also give good reviews for catching snakes and tarantulas that they then stomp on to 'finish the job'.... hum, now that I type these things out, I am thinking they should outlaw sticky traps as cruel