What you feed a beetle depends entirely on the species, but most pet beetles fall into a few broad categories: fruit eaters, sap feeders, scavengers, and predators. The good news is that beetle diets are simple and inexpensive once you know what your species needs. Here’s a practical breakdown covering the most commonly kept groups.
Fruit-Eating and Sap-Feeding Beetles
The most popular pet beetles, including rhinoceros beetles, Hercules beetles, and flower beetles, eat fruit and tree sap as adults. In the wild, stag beetles are highly dependent on living trees where they feed on sap flows. Adults are also commonly found feeding on decaying fruits. You can replicate this at home with soft, ripe fruits like banana, apple, peach, and melon. Cut fruit into small pieces or slices and place them directly in the enclosure.
Beetle jelly, a commercially available sugar-based gel sold at pet shops and online, is the most convenient staple for these species. It comes in small cups that fit neatly into the enclosure and resists mold better than fresh fruit. Many keepers use beetle jelly as the primary food and offer fresh fruit as an occasional supplement. Stag beetles are particularly drawn to fermented, sugary substances. Traps used by researchers to attract wild stag beetles are baited with red wine, white wine, and sugar, which gives you a sense of how strong their preference for sweet, fermented foods is.
Replace fresh fruit every one to two days before it molds. Beetle jelly cups can last a bit longer but should be swapped out once they dry up or get contaminated with substrate. Feeding once or twice a day works well for most species, though many keepers simply keep a jelly cup available at all times and let the beetle eat freely.
What Beetle Larvae Need
If you’re raising beetle larvae (grubs), their diet is completely different from the adults. Larvae of rhinoceros beetles, stag beetles, and similar species feed on decaying organic matter, primarily rotting wood and leaf litter. The two main substrates used by hobbyists are flake soil and kinshi.
Flake soil is fermented hardwood sawdust or wood chips that have been broken down by microorganisms, typically yeast. It mimics the rotting wood that larvae consume on the forest floor. You can buy it premade or ferment your own using hardwood sawdust mixed with water over several weeks. The key is that the wood must be well decomposed. Fresh sawdust is indigestible to larvae.
Kinshi is a step up in nutrition. It’s hardwood sawdust colonized by oyster mushroom mycelium, packed into bottles or bags. The fungal growth pre-digests the wood fibers, making them far more nutritious and easier for larvae to consume. Commercial kinshi produced in Japan often includes additives like wheat bran, soy protein isolate, calcium, and glutamic acid to boost the nutritional profile for faster larval growth. Stag beetle larvae in particular tend to grow larger and faster on kinshi compared to flake soil alone.
Larvae eat constantly and live inside their food substrate, so the main task is making sure they don’t run out. Check the container every few weeks. When the substrate has been largely converted to frass (larval droppings, which look like small dark pellets), it’s time to replace or supplement it with fresh material.
Predatory Beetles
Ladybugs and ground beetles are the most common predatory beetles people encounter or keep. Ladybugs are well-known predators of soft-bodied insects, especially aphids, but they also eat scale insects, whiteflies, and psyllids. If you’re keeping ladybugs, you can collect aphids from garden plants or purchase them from biological supply companies. Small amounts of pollen, raisins soaked in water, or a dab of honey can serve as supplemental food when live prey isn’t available.
Ground beetles are generalist predators that eat a wide range of small invertebrates, including worms, slugs, and other insects. In captivity, they do well on small pieces of raw meat, crushed insects, or commercially available feeder insects like flightless fruit flies.
Scavenger and Carrion Beetles
Dermestid beetles are the most widely kept scavenger species, often maintained in colonies for taxidermy work or skull cleaning. These beetles require a diet rich in protein and fat, so fresh raw meat is the ideal food source. Small pieces of chicken, beef, or fish work well. Dried meat, pet jerky, and even dry dog food can serve as backup options.
Moisture management matters more with dermestids than with most other beetles. They extract water from the food they eat, but in dry environments they may need a supplementary water source. Water gel crystals, the same kind used for feeder insects, work well because they provide hydration without adding the dampness that encourages mold. Keep the substrate dry at all times, since mold growth is one of the biggest threats to a dermestid colony.
Foods to Avoid
Citrus fruits are generally a poor choice for fruit-eating beetles. The acidity can irritate them, and most species show little interest. Avoid processed or seasoned foods, anything with salt, and pesticide-treated produce. If you’re collecting leaves or wood from outdoors for larvae, make sure the source hasn’t been sprayed with herbicides or insecticides.
Moldy food is a common problem in humid beetle enclosures. Fruit left too long will grow mold that can harm both adult beetles and larvae. Remove uneaten food promptly and keep the feeding area as clean as practical without disturbing the beetle’s habitat too much.
Supplements and Nutrition Boosting
Most adult beetles don’t need dietary supplements if they’re getting a varied diet appropriate to their species. Larvae benefit more from nutritional enrichment, which is why kinshi with added protein and calcium outperforms plain flake soil for many species.
If you’re raising beetles as feeder insects for reptiles or other pets, gut-loading is an effective strategy. Research published in the American Journal of Veterinary Research found that mealworm larvae fed a high-calcium diet for just 48 hours absorbed enough calcium to meet dietary recommendations for vertebrate animals eating them. The larvae were simply placed on the calcium-rich substrate and allowed to feed normally. This 48-hour window is consistently sufficient for maximizing calcium content in feeder beetle larvae.
Feeding Schedule and Portions
Adult beetles don’t eat large amounts. A single beetle jelly cup or a thumbnail-sized piece of fruit is plenty for one beetle per day. Offering food twice daily, once in the morning and once in the late afternoon, works well for active species, but once daily or even every other day is fine for less active beetles. Younger, more active beetles eat proportionally more than older adults approaching the end of their lifespan.
The simplest approach is to always have food available and let the beetle regulate its own intake. Watch for untouched food, which signals you’re offering too much or the wrong type, and adjust from there.