"Feeder insects" cross every taxonomic line in the reptile room, but the animals eating them don't respond to the same feeding rules. Compare a bearded dragon, a Pacman frog, and a tarantula side by side and the differences aren't cosmetic — they come down to skeleton, metabolism, and where vitamin D actually comes from.
Skeleton and Calcium
Reptiles and amphibians are vertebrates that build and maintain actual bone, so a calcium-poor feeder insect diet puts them at real risk of metabolic bone disease — bearded dragons are especially prone to it. Arachnids like tarantulas and emperor scorpions have no bone at all — they grow by molting a chitin exoskeleton, and a peer-reviewed study of tarantula hemolymph found calcium and vitamin D3 levels suggesting these processes "may play a minimal or no role in calcium metabolism in spiders." Dust for the first group; skip it entirely for the second.
Feeding Frequency: Metabolism Sets the Clock
Reptiles and amphibians generally eat on a schedule tied to age and season — daily for insect-heavy hatchlings, tapering to a few times a week as adults, and dropping further in cool weather. Arachnids run on a much slower metabolism: an adult tarantula or emperor scorpion may only take prey once every one to two weeks, and both stop eating entirely for days to weeks around a molt. Feeding a tarantula on a bearded dragon's schedule isn't more attentive care — it's overfeeding.
Where Vitamin D Comes From
Reptiles kept under UVB synthesize vitamin D3 in their skin the way many vertebrates do; species commonly kept without UVB, like nocturnal, fossorial Pacman frogs, get it exclusively through dietary D3 dusting instead. Arachnids need neither pathway — with no bone to mineralize, dietary or UVB-sourced D3 has nothing to act on.
Bottom Line
Reptile and amphibian feeding revolves around a real, ongoing calcium requirement that shifts with UVB access; arachnid feeding revolves around a slow metabolism and a molt cycle, with no calcium requirement at all. Same feeder insects, different rulebook — check our feeder guides for your specific species.
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