Black Soldier Fly Larvae vs. Discoid Roaches for Blue Tongue Skinks
I keep feeder colonies for a mixed reptile collection, and blue tongue skinks are one of the easiest animals to feed well — they're omnivores, so you're never locked into a single prey item. The two feeders that come up most often for skinks are black soldier fly larvae (BSFL, often sold as "Phoenix worms" or "calci-worms") and discoid roaches (Blaberus discoidalis). People treat it like an either/or decision. It isn't. Each one does a specific job, and once you understand what each brings, you'll reach for both.
This is the honest head-to-head: nutrition, calcium, digestibility, handling, and exactly when I use each.
What a blue tongue skink actually needs
Blue tongue skinks are omnivores with a slow metabolism and a real tendency toward obesity in captivity. A good adult diet runs roughly 40-50% animal protein, around 40% vegetables (mostly leafy greens), and about 10% fruit as the occasional treat. Juveniles tilt more toward protein because they're growing fast.
The protein portion is where feeders come in, and the two big jobs that portion has to do are: deliver lean, digestible protein without packing on fat, and supply (or be supplemented to supply) calcium. Calcium matters more than almost anything else, because chronic calcium shortfall causes metabolic bone disease (MBD) — a preventable, disfiguring condition that the MSD Veterinary Manual flags as one of the most common nutritional disorders in captive reptiles. Keep that lens on as we compare, because it's where the two feeders genuinely differ.
Black soldier fly larvae: the calcium feeder
BSFL are the larval stage of Hermetia illucens, a clean, non-pest fly raised on controlled diets. They're small, soft, plump, and they wriggle — which is exactly what makes a skink's hunting reflex fire.
Their standout trait is real and worth repeating: BSFL have a naturally favorable calcium-to-phosphorus ratio. This is unusual. Most feeder insects are phosphorus-heavy and need calcium dusting to be safe long-term. BSFL are the rare feeder that arrives with the calcium already built in, which makes them genuinely useful for preventing MBD and ideal for growing juveniles.
A few more honest points in their favor:
- Soft-bodied and low in chitin, so they're easy to digest and gentle on juveniles, seniors, and any skink recovering from illness.
- Low maintenance. They keep for weeks in their cup at cool room temperature (mid-50s to low-60s °F) with no feeding required. For a busy keeper that's a real perk.
- Odorless and clean.
The trade-off: they're small. For a full-grown blue tongue skink, a few larvae aren't a meal — you'd need a generous portion. They're a supplement and a calcium booster more than a one-feeder staple for an adult.
Discoid roaches: the protein staple
Discoid roaches are a tropical, non-climbing roach native to Central and South America, reaching about 1.5-2 inches as adults. They're the workhorse staple feeder for a lot of reptile keepers, and for an adult blue tongue skink they're close to ideal as the backbone of the protein portion.
Why they earn the staple slot:
- Meaty and substantial. One or two adult discoids is an actual meal for an adult skink, not a snack.
- High protein (~20-23%), moderate fat (~7-9%), softer/lower-chitin shell than crickets, so they digest cleanly with low impaction risk.
- They can't climb smooth surfaces and they don't fly. A smooth-walled bin contains them, which makes feeding and keeping a colony genuinely low-stress. (You'll see old care sheets call them "skilled escapists" — that's wrong for adults on smooth glass or plastic.)
- Nearly odorless and they breed into a self-sustaining colony, so you can produce your own feeders cheaply.
The one correction I'll make to the usual roach hype: discoids do not have a "favorable" calcium-to-phosphorus ratio. Like crickets, superworms, and almost every other feeder, they're phosphorus-heavy. That's not a knock — it just means you dust them with calcium, which takes two seconds and closes the gap.
Head-to-head
Treat these as approximate, as-fed figures — real values shift with diet and source — but the relationships are reliable:
| Factor | Black soldier fly larvae | Discoid roach |
|---|---|---|
| Protein | Moderate (~17-20%) | High (~20-23%) |
| Fat | Low-moderate | Moderate (~7-9%) |
| Calcium:phosphorus | Favorable (the exception) | Phosphorus-heavy (dust it) |
| Size / meal value | Small — supplement | Substantial — staple |
| Chitin / digestibility | Very soft, easy | Soft, easy |
| Best for | Juveniles, calcium, sensitive guts | Adult staple protein |
| Storage / care | Weeks in a cup, no feeding | Living colony, low effort |
| Hydration | Moderate | Moderate |
How I actually feed them
For a healthy adult blue tongue skink, I build the protein portion on discoid roaches — they're filling and clean — and I rotate BSFL in regularly for the calcium and variety. Even with BSFL in the mix, I still dust the discoids with a calcium supplement (calcium with D3 on the schedule your setup requires).
For a juvenile, I lean harder on BSFL early because the built-in calcium supports fast bone growth, then phase in appropriately sized discoid nymphs as the skink grows.
For a senior or a skink with digestive trouble, BSFL win on softness and ease.
The universal rules don't change: size the feeder no larger than the space between the skink's eyes, dust with calcium, gut-load the feeders for 24-48 hours before offering, and rotate variety so no single feeder dominates. If you want to keep a steady supply of meaty staple feeders on hand, All Angles Creatures stocks healthy discoid roaches sized for everything from juveniles to adults.
Gut-loading both feeders
Whatever you feed, what the feeder ate becomes what your skink eats. For 24-48 hours before offering, give both feeders nutrient-dense food:
- Discoids gut-load beautifully — offer rich produce (carrot, squash, leafy greens, sweet potato) plus a quality dry roach chow, then harvest. They'll be packed with nutrients at the moment your skink eats them.
- BSFL come pre-loaded with calcium and don't need heavy gut-loading, but keeping them on a clean bran or chow substrate maintains their condition.
This single habit does more for a skink's long-term health than most supplements.
Portions and frequency
Blue tongue skinks have a slow metabolism and overeat readily, so portion control is real care, not stinginess:
- Juveniles: feed more often — most of the diet protein-forward, with insects offered several times a week, alongside finely chopped greens. BSFL early for the calcium; appropriately sized discoid nymphs as they grow.
- Adults: the plate shifts toward greens. A few discoids (with BSFL worked in) a couple of times a week is typical. Watch body condition — a skink that's getting chunky needs fewer feeders and more greens.
- Always size the feeder no larger than the space between the skink's eyes, and dust the discoids with calcium.
Common mistakes I see
- Treating one feeder as the whole diet. Neither BSFL nor discoids alone is complete. Rotate, and keep greens central.
- Skipping calcium on discoids because a care sheet claimed they're "balanced." They aren't — dust them.
- Overfeeding insects to an adult. Obesity is the most common blue tongue skink health problem; protein is the part to ration as they age.
- Feeding wild-caught insects. Pesticide and parasite risk. Use captive-bred feeders only.
- Feeding only dried BSFL with no hydration. Dried larvae are fine, but soak them and make sure the skink has other water sources.
Reading your skink's condition
The feeders are working if the skink is. A well-fed blue tongue skink has a firm, rounded body without a fat pad bulging at the base of the tail or under the chin, alert eyes, smooth shed cycles, and steady appetite. Signs you've drifted off course:
- Soft jaw, rubbery limbs, tremors, or reluctance to move point to calcium shortfall / early MBD — tighten up calcium dusting and UVB, and lean on BSFL's built-in calcium. Get a vet involved if it's pronounced.
- Obvious fat deposits and a heavy, sluggish skink mean too much protein/fat — cut insect frequency, especially fatty feeders, and push greens.
- Refusing food can mean it's too cool, stressed, or simply full — check temperatures before assuming a problem.
The feeders are only one input; pair them with proper UVB, basking heat, and a greens-forward plate and the whole picture comes together.
The bottom line
Stop framing it as BSFL or discoids. Discoids are the staple; BSFL are the calcium-rich supplement. Run discoids as the protein base, work BSFL in for calcium and for any skink that needs a softer feeder, dust everything appropriately, and keep greens at the center of the plate. That rotation covers a blue tongue skink's protein needs better than either feeder could alone.
Want to go deeper on the staple? See my complete playbook for keeping and breeding discoid roaches, or browse the full feeder insect care library.