How to Raise Larvae

Everything you need to know about raising beetle larvae (grubs) from egg to adult. Covers substrate, feeding, temperature, container sizes, and the pupation process for stag, rhino, and flower beetles.

Understanding Beetle Larvae

Beetle larvae (also called grubs) look like white or cream-colored C-shaped worms. All beetle larvae go through 3 stages called instars: L1 (tiny, just hatched), L2 (medium), and L3 (large, final stage before pupation). The larval stage is when the beetle does all its growing — the size of the adult is entirely determined by how well you raise the larva.

Key Principles (All Types)

• Substrate = food — larvae eat the substrate they live in. The quality of substrate directly determines adult size.
• Don't disturb too often — check larvae once every 2-4 weeks at most. Stress reduces growth.
• Temperature matters — cooler temperatures generally produce larger adults (within the safe range for each species).
• Container size affects growth — larger containers give larvae more food and room to grow bigger.
• Individual housing recommended — especially for stag beetle larvae, which can be cannibalistic.

What They Eat

Stag beetle larvae are wood eaters. In nature, they live inside and eat decaying hardwood. In captivity, you feed them flake soil (fermented hardwood sawdust) — this is the #1 most important supply for raising stag beetles.

Container Sizes

• L1 larvae — 200ml cup or small container. Tiny larvae don't need much space.
• L2 larvae — 500ml-800ml container. Move up when the larva outgrows the small cup.
• L3 larvae — 800ml-1500ml container for most species. Large species (Dorcus titanus, Hexarthrius) benefit from 1500ml-2000ml.

Substrate Changes

Replace the substrate when it turns into fine, dark frass (larva poop) — usually every 2-3 months. You'll notice the substrate changes from fluffy brown to grainy dark brown/black. When more than 70% looks like frass, it's time to change.

1. Prepare new flake soil in the container (moisten it — squeeze test: a few drops when squeezed)
2. Gently dig out the larva from the old substrate
3. Make a small hole in the new substrate and place the larva in
4. The larva will burrow down on its own — don't push it in

Temperature Guide

Stag beetles generally prefer cooler temperatures than rhino or flower beetles. Keeping larvae at the lower end of the safe range (while still within species requirements) tends to produce larger adults — but it also means a longer larval period.

Pupation

When the L3 larva is ready to pupate, it stops eating, shrinks slightly, and turns yellowish. It will build a pupal cell — a smooth, oval chamber in the substrate. This is critical: do NOT disturb a larva that is building or inside a pupal cell.

• Pupation takes about 3-6 weeks
• After pupating, the new adult stays in the cell for another 2-6 weeks while the exoskeleton hardens
• Do not dig up the beetle until it has fully colored up and started moving around

What They Eat

Rhino beetle larvae eat decomposed organic matter — primarily leaf mulch, compost, and fermented wood. They are less picky than stag beetle larvae and will eat a wider range of substrates. A good mix is flake soil + leaf litter compost + organic soil.

Container Sizes

Rhino beetle larvae grow much larger than stag beetle larvae — some species (Dynastes, Megasoma) produce larvae that weigh over 100 grams. They need significantly bigger containers.

• L1 larvae — 500ml container
• L2 larvae — 1-2 liter container
• L3 larvae — 3-8 liters for medium species, 8-16+ liters for large species (Dynastes hercules, Megasoma)

Substrate Recipe

A proven substrate mix for rhino beetle larvae:

• 50% fermented hardwood flake soil
• 30% leaf litter compost (decomposed oak or beech leaves)
• 20% organic potting soil (no fertilizer or chemicals!)

Mix well and moisten to the squeeze test level. Some breeders add crushed dried leaves on top as extra food.

Substrate Changes

Rhino beetle larvae produce a lot of frass because they eat a lot. Change substrate every 2-3 months or whenever more than 60% has turned to frass. For large species in the final L3 stage, you may need to change more frequently.

Pupation

Rhino beetle larvae build large pupal cells deep in the substrate. For large species, the pupal cell can be the size of a fist or larger. The larva uses its own frass mixed with substrate to build a hard-walled chamber.

• Pre-pupa stage (stops eating, shrinks) lasts 2-4 weeks
• Pupation lasts 4-8 weeks depending on species and temperature
• New adult stays in pupal cell for 3-8 weeks while hardening
• Total time from pre-pupa to adult emergence: 2-4 months

What They Eat

Flower beetle larvae (Cetoniinae) eat a mix of flake soil and leaf litter, similar to rhino beetles but they tend to prefer finer-textured substrate. Many species also accept plain compost. They are the least picky of all three beetle types.

Container Sizes

Flower beetle larvae are smaller than stag or rhino larvae, and many species can be raised communally (multiple larvae in one container) without cannibalism issues.

• Individual rearing — 200-500ml cups for most species
• Communal rearing — 5-10 liter box for 5-10 larvae of the same species
• Large species (Mecynorrhina, Goliathus) — 1-2 liters per larva individually

Substrate Recipe

• 40% flake soil (fine grade)
• 40% leaf litter compost
• 20% coconut fiber or peat moss for moisture retention

Some breeders add protein supplements for large flower beetle species — dog food pellets (crushed) or fish flakes mixed into the substrate can boost larval growth, especially for Goliathus and Mecynorrhina larvae.

Communal Rearing

Unlike stag beetles, most flower beetle larvae can be raised together without fighting or cannibalism. This makes them much easier to manage in large numbers.

• Group larvae by size (don't mix L1 with L3)
• Don't overcrowd — about 500ml-1L of substrate per larva
• If you notice larvae disappearing, the species may be cannibalistic — switch to individual cups

Pupation

Flower beetle larvae build a special pupal cell called a cocoon — they use substrate particles mixed with a secretion to create a hard, round shell. This cocoon is much tougher than stag or rhino beetle pupal cells.

• Pupation takes 3-5 weeks
• The cocoon is sealed and should NOT be opened
• New adult breaks out of the cocoon on its own when ready
• Total cycle (egg to adult): 4-8 months for most species — the fastest of all three types

Common Problems & Solutions

Quick Comparison