If you ever spot any insects in a terrarium, they�re usually harmless and it�ll be your ultimate decision keeping it or removing it. Common bugs include: caterpillar, beetles, spiders, which don�t affect the terrarium�s environment whatsoever. If you decide leaving them alone, they�ll eventually die on their own and then they can be removed with a cotton swab, twizzles or a long stick. We do not recommend using insecticides or other chemicals to get rid of bugs, there is a chance of harming or even killing the terrarium.