Pachnoda marginata, the sun beetle, is a flower beetle (subfamily Cetoniinae) from West Africa. If you've heard anyone recommend a "first beetle," it was probably this one. They're cheap, colourful, breed easily, and have a fast life cycle. Here's how to keep them properly.
Adults
Adult sun beetles are about 2-3cm long, bright yellow-orange with brown or black markings. They're diurnal, meaning they're active during the day, which makes them more fun to watch than species that only come out after dark. You'll see them climbing, flying short distances in their enclosure, and feeding.
House adults in a well-ventilated container. A plastic faunarium or similar tub works fine. Give them a few centimetres of substrate to walk on, a piece of bark or cork to climb, and food. The enclosure doesn't need to be large; a 5-litre container is adequate for a small group of three to five adults.
Feed ripe banana, apple, or mango, and supplement with beetle jelly. Sun beetles aren't fussy eaters. Replace fruit before it moulds, which usually means every one to two days depending on temperature. Beetle jelly lasts a bit longer and is less messy.
Adults live roughly two to four months. Males tend to have a slightly shorter lifespan than females. They'll mate readily without any special encouragement; just having males and females in the same container is usually enough.
Breeding
To breed, you need to provide a suitable egg-laying substrate. Fill the enclosure with at least 15cm of moist flake soil or a mix of fermented wood, leaf litter, and coco coir. Females burrow down into the substrate to lay eggs individually. A single female can produce several dozen eggs over her adult lifespan.
Keep the breeding enclosure at 22-26C. The substrate should be moist but not waterlogged. You can continue feeding the adults on the surface while the eggs develop below.
Eggs hatch in roughly two to four weeks. The tiny L1 larvae will begin feeding on the surrounding substrate immediately. You can either leave them in the breeding container until they reach L2 (which makes them easier to handle) or separate them earlier if you want to track individuals.
Larvae
Sun beetle larvae are relatively forgiving compared to many other species. They'll do well on fermented hardwood flake soil, and they'll also accept a simpler mix of well-rotted wood and leaf litter with some coco coir. The substrate doesn't need to be as refined as what you'd prepare for, say, Mecynorrhina larvae.
Individual rearing containers of about 500ml to 1 litre are fine per larva, filled to a depth of at least 10-12cm. Top up or replace substrate as the larvae eat through it. You'll see it gradually turn into dark, granular frass.
The larval stage takes roughly three to five months, passing through L1, L2, and L3 instars. L3 larvae will reach about 3-4cm in length and look like plump, cream-coloured grubs with a brown head capsule.
Temperature during the larval stage should be around 22-26C. Like most beetles, warmer temperatures produce faster development but potentially smaller adults. Cooler conditions slow growth but can yield slightly larger beetles.
Pupation
When the L3 larva is ready to pupate, it stops feeding and constructs a pupal cell from compressed substrate. The cell is a smooth, oval chamber about the size of a large grape. Once you notice a larva has stopped eating and become less active, resist the urge to check on it. The pupal cell is fragile, and breaking it usually means a dead or deformed beetle.
Pupation takes roughly three to six weeks at 24C. After that, the adult beetle ecloses inside the cell, waits for its exoskeleton to harden, and then digs its way to the surface. Newly eclosed adults are pale and soft for the first few days. Leave them alone until they've fully darkened and hardened before offering food or handling them.
Common issues
Larvae not growing: Usually a substrate problem. If you're using plain soil, compost, or unfermented wood, the larvae can't extract enough nutrition. Switch to proper fermented hardwood flake soil.
Mould on food: Normal, especially in warm, humid conditions. Remove mouldy food and replace it. Small amounts of white mould on the substrate surface are harmless.
Grain mites: The fine white dust that sometimes appears on food and substrate. They're not harmful to beetles but indicate conditions are too moist or there's uneaten food sitting around. Improve ventilation and reduce feeding slightly.
Adults not breeding: Make sure you have both sexes. Males tend to have a slightly more pronounced bump or indentation on the underside of the abdomen compared to females, though sexing Pachnoda reliably takes a bit of practice. Also check that the substrate is deep enough and moist enough for egg-laying.
Why sun beetles are worth keeping
The whole life cycle, from egg to adult to eggs again, plays out in well under a year. That means you get to observe every stage of complete metamorphosis in a reasonable timeframe, and you get feedback quickly. If something's wrong with your husbandry, you'll find out in weeks rather than months. And if everything goes right, you'll end up with more beetles than you know what to do with, which is the best kind of problem.