depends on the bug! in general most bugs will just not eat if they don’t feel hungry. quite often my amblypygi and centipedes refuse food, and will do so for long periods of time when close to molting.
many herbivores or detritivores like slugs, caterpillars, millipedes, isopods, or cockroaches will eat plant matter all day until they meet their needs. however, for certain animals. captive diets can be too rich in nutrients. most roaches are adapted to eat low-protein diets and therefore store protein efficiently as uric acid crystals. in captivity, too much protein essentially give roaches gout and can kill them, so dog/cat/fish food should be given in moderation (depending on species, 20-30% protein is more than enough and less is fine, I raise B. dubia entirely on vegetable and fruit scraps).
predatory bugs also can be overfed. some tarantulas can become obese which is concerning for them since they have thin, soft abdomens which rupture easily, so obese tarantulas are more susceptible to injury and molting failure. my A. chalcodes Cassandra hasn’t eaten since the previous autumn and not lost any weight, so it seems to depend on the species and individual’s metabolism if they’ll overeat. some centipedes can look awfully bloated in captivity, but not enough is known about them to say if that’s unhealthy. I try to keep my centipedes fairly slim, and mine seem to not feed if they’re not hungry as well.
in general, my advice for feeding arthropods is to try and mimic natural diets as much as possible. slugs and caterpillars need to eat constantly to extract nutrients from their watery, fibrous plant diets, so should always have food available. cockroaches, millipedes, and isopods are detritivores, so should always have dead leaves or vegetable bits to eat, and protein can be offered in moderation as needed. predators should be fed plenty after molting, and maintained not-at-bursting for the rest of that instar