What Size Feeder Insect Does My Reptile Need?
Ordering the wrong size is the single most common mistake in buying feeder insects, and it is almost entirely avoidable.
The rule
Never feed an insect wider than the space between your reptile's eyes.
It is crude, it is not species-specific, and it is still the most useful thing anyone will tell you. Prey wider than that gap is difficult to swallow and, in animals like bearded dragons, is associated with impaction — one of the most common preventable illnesses in captivity.
Note that it is width, not length. A long, slender feeder is usually fine; a short, broad one may not be.
Where the rule needs adjusting
Leopard geckos are often given a slightly different measure: no longer than the width of the head. Both rules land in roughly the same place.
Crested geckos have narrower heads than a similarly sized leopard gecko and are more easily put off by prey that looks like a fight. Size down.
Chameleons will frequently attempt prey that is too large for them. The judgment has to be yours rather than the animal's.
Growing animals need re-checking. A size that was right for a juvenile bearded dragon three months ago is probably not right now.
Feeders that change size after you buy them
Hornworms grow quickly, and the size you receive can change substantially within days of arrival. If your animal needs smaller prey, plan for that growth rather than ordering the size you need today and hoping it holds.
When you are between two sizes
Take the smaller one. A feeder that is slightly too small is eaten. A feeder that is slightly too large is a risk, and often simply refused.
Read next
Feeder Size Guide · Feeding bearded dragons · Feeding leopard geckos
General guidance only. Reptile dietary needs vary by species, age, size and health. Follow feeding recommendations appropriate for your individual animal.