What Size Discoid Roach Should I Feed My Reptile? A Species-by-Species Guide

"What size roach should I feed my [bearded dragon / leopard gecko / chameleon]?" is one of the questions I get most, and it's a good one — because feeder size matters more than most keepers realize. Too large and you risk choking, impaction, and stress. Too small and your animal burns energy chasing prey that doesn't deliver enough nutrition per catch.

The rule that governs all of it is simple: never feed an insect wider than the space between your reptile's eyes. That applies to every feeder, not just roaches. The space between the eyes roughly corresponds to the width of the esophagus, so prey that fits that guideline passes safely through the digestive tract. Memorize that one sentence and you've got the foundation.

Below, I break it down by species and age. All sizes reference standard discoid roach (Blaberus discoidalis) grades.

The three discoid roach size grades

Discoids are sold in three working grades, and these are the references I use throughout this guide:

• ◆Small (nymphs): roughly ¼–½ inch. Tiny, soft-bodied nymphs for small reptiles and juveniles.
• ◆Medium: roughly ¾–1 inch. The most versatile size — right for the widest range of reptiles.
• ◆Large (sub-adult to adult): roughly 1¼–1¾ inches. Full-sized roaches for big reptiles with big appetites.

Why discoids make sizing easy

Before the species breakdown, a quick word on why I size most of my collection on discoids specifically. They come in clean, predictable grades, they don't climb smooth walls or bite, they're soft-bodied and low in chitin (easy to digest, gentle on a small reptile's gut), and they gut-load well — meaning whatever you feed the roach becomes nutrition for your animal. A staple feeder you can size precisely is half the battle in feeding a reptile correctly. For the full keeping-and-breeding picture, see my discoid roach playbook.

One nutrition note that applies to every size: like nearly all feeder insects, discoids are phosphorus-heavy with a poor calcium-to-phosphorus ratio. That's why dusting with a calcium supplement is non-negotiable regardless of how well the roach is gut-loaded, and why size alone doesn't make a feeder complete — size keeps it safe, dusting keeps it nourishing.

Bearded dragons

Bearded dragons grow fast, and the feeder size should scale with them across their whole life.

Baby (0–3 months) — small nymphs. Babies are tiny with narrow throats. Feed only small discoid nymphs, as many as they'll take in a 10–15 minute session, 2–3 times a day. Insects should make up 70–80% of the diet at this stage.

Juvenile (3–8 months) — small to medium. As the dragon grows, gradually mix mediums in alongside smalls. Feed 2–3 times daily, as many as they'll eat in 10–15 minutes. Insects are still roughly 60–70% of the diet.

Sub-adult (8–14 months) — medium to large. Most sub-adults handle mediums comfortably, with larger individuals ready for large discoids. Drop to once daily and start building the vegetable share toward 40–50%.

Adult (14+ months) — large. Full-grown dragons thrive on large discoids. Feed 10–20 large roaches 2–3 times a week, with the diet shifting to roughly 50–60% vegetables and 40–50% insects. Big males can take the largest adult discoids without trouble.

Leopard geckos

Leopard geckos are smaller than dragons and stay insectivores for life — sizing is especially important because they never eat vegetables to round out their nutrition. (For the full husbandry picture, see my leopard gecko care guide.)

Hatchling & juvenile (0–6 months) — small nymphs only. Use the smallest small discoid nymphs. Young leos have tiny mouths and are prone to impaction from oversized prey. Feed daily, 5–8 appropriately sized nymphs per session.

Sub-adult (6–12 months) — small to medium. Transition to larger smalls and start introducing small-end mediums. Feed every other day, 5–8 insects per session.

Adult (12+ months) — medium. Medium discoids are ideal: big enough to be nutritionally meaningful, small enough to swallow safely. Feed every 2–3 days, 5–8 roaches per session. Most adult leos should not get large adult discoids — they're too big for the average leo's mouth.

Chameleons

Chameleon sizing depends heavily on species. A full-grown male panther can eat much larger prey than a Jackson's or a juvenile veiled.

Juveniles (all species) — small nymphs. Soft small nymphs are safe and appropriate. Feed daily, 8–15 small nymphs depending on species and appetite.

Adult veiled & panther — medium. Medium discoids are the sweet spot for most adults. Feed 5–10 every other day as part of a varied rotation. Large roaches are usually unnecessary and can be too big for some individuals.

Adult Jackson's & smaller species — small to medium. Smaller species should stick to smalls and small-end mediums. Jackson's in particular have small mouths relative to body size.

Monitors and tegus

These large lizards have big appetites and handle the biggest feeders available.

Juvenile monitors & tegus — medium to large. Even juvenile savannah monitors, Ackie monitors, and Argentine tegus usually manage medium discoids from an early age. Move to large as the animal grows.

Adult monitors & tegus — large. Large discoids are the right feeder size, and these animals can eat a dozen or more per session. For adult savannah monitors and Argentine tegus, supplement large discoids with other substantial prey as part of a varied diet.

Quick reference for other species

• ◆Crested geckos: small nymphs only (adults may take a medium occasionally). More in my crested gecko care guide.
• ◆Blue tongue skinks: medium to large, depending on animal size.
• ◆Dart frogs: smallest available nymphs only — tiny, fruit-fly-sized prey.
• ◆Tarantulas: match roach size to the spider's body — small nymphs for slings, medium for juveniles, large for adults.
• ◆Pacman frogs: medium for juveniles, large for adults.
• ◆Tree frogs: small to medium depending on species.

How many to feed, and how often

Size answers "how big," but keepers always ask "how many" in the same breath, so here's the pairing in plain terms. Growing juveniles of any species eat more often — daily or near-daily — because they're building body mass fast, and you offer as many feeders as they'll take in a focused 10–15 minute window (for dragons and chameleons) or a fixed small count (5–8 for young geckos). Adults slow down: every other day to every 2–3 days for most insectivores, with the count steady rather than free-fed. The reliable signal you're feeding too much is body condition — a leopard gecko's tail wider than its neck, or a chubby, lethargic dragon. Scale frequency, not feeder size, to manage weight.

Two more habits that matter as much as size:

• ◆Gut-load 24–48 hours before feeding. Give the roaches quality produce and protein before you offer them, so they're packed with nutrients at the moment your animal eats them.
• ◆Dust right before feeding. Toss the sized feeders with calcium (and a multivitamin on schedule) so the supplement is fresh on the roach when it goes down.

Why getting size right matters

The two failure modes are worth understanding so the rule sticks. Impaction is a gut blockage that happens when prey (or substrate) is too large to pass — it's a genuine veterinary emergency and one of the most preventable problems in the hobby. Choking and stress come from prey that's simply too big to handle. On the other end, prey that's too small wastes the animal's energy. The space-between-the-eyes rule threads that needle. For the clinical background on impaction and reptile feeding, the MSD/Merck Veterinary Manual is a reliable neutral reference.

How to actually measure "the space between the eyes"

The rule sounds precise, but in practice you're eyeballing it, so here's how I make it reliable. Look at your reptile head-on and gauge the width across the head between the two eyes — that's your maximum prey width. Then hold a roach up next to the animal (or next to a photo on your phone) and compare. If the roach is clearly narrower, it's safe; if it's close or wider, size down. For a hatchling whose head is tiny, this matters most — young animals have the narrowest throats and the highest impaction risk, which is why I default to the smallest nymphs for anything under a few months old and only size up once I've watched the animal handle the current grade cleanly.

It's worth repeating that length is not the constraint — width is. A long, slim feeder can be fine where a short, fat one isn't, because it's the widest point that has to pass the throat. Discoids are relatively flat and oval, which works in your favor here.

When in doubt, go smaller

If you're unsure which size to choose, always err smaller. A reptile that eats several small feeders gets the same nutrition as one eating fewer large feeders — without the choking or impaction risk. You can always size up on the next order once you've confirmed your animal handles the current size comfortably.

Discoids make this easy because they come in clean small, medium, and large grades, all gut-loaded so the nutrition is there regardless of which size your animal needs.

For more on building a healthy feeder rotation, see why silkworms are the best feeder for picky reptiles and the complete How to Keep Discoid Roaches Alive playbook, or browse the full exotic animal care library.