Fungus gnats (or sciarid fly) are another massive pet hate for houseplant growers. They are the denizens of overwatered and poorly drained soils. I include them here for completeness, but they aren’t too much of an issue for orchids. They might be seen if you grow Bulbophyllum or other moisture loving genera in Sphagnum moss. The flies are mostly an annoyance rather than an actual problem, and the larvae which are often accused of eating roots are eating fungi in saturated soil and it’s the wet soil that damages roots. They are easy to deter by using well drained potting media and avoiding peat-based composts (as if we needed another reason to exclude peat from our growing media). Consider mulching your plants. You can use sticky traps to catch the flying adults, but it is better to just tweak your watering and growing medium. You’ll have less pests and better plants.