Scale will produce a sticky residue known as 'excretion', which is the prominent symptom of an attack. Visit this article to learn about addressing an attack and its sticky counterpart.
Click here to learn about the annoying, yet harmless Fungus Gnat - & how to eradicate an infestation!
Click here to learn more about its life cycle, eradication of an infestation & which products are best.
Although Snails and Slugs aren't likely to attack your houseplants, here's an article about eradicating the pests for when the worst becomes a reality.