Rhino Beetles
Rhino Beetles are the most sought after live beetle pets in the hobby, and for good reason. They are famously huge insects! Like their familiar mammalian namesake, many species boast a large top horn projecting forwards from the thorax. A bottom horn may also juts upward from the head.
Adults are relatively simple to keep, and so are larvae. The United States has numerous rhino beetle species that make it into the pet trade on a limited basis, but two species especially are always in high demand. The Eastern US offers up Dynastes tityus. These often have a yellow color, like a very ripe banana. Their top horn tends to be about the same length as the bottom horn. The Western species, Dynastes granti, has a body shape more similar to the gigantic South American Dynastes hercules beetles, with their significantly longer top horn.
Both US Dynastes are usually available in the hobby on a yearly basis (I know a place), usually in the warmer months but extending a bit into the fall season, if not winter. The D. tityus distinctly make better pets because they are longer lived in captivity. Yet, few will disagree that D. granti make for more impressive dead specimens (and they often only live a few months as adults, in captivity).
What follows are some basic recommendations for keeping them, but a serious hobbyist should definitely consider investing in the book: The "Complete Guide to Rearing the Eastern Hercules Beetle and Other Rhinoceros Beetles" by Orin McMonigle. It is available, HERE!
Below, I will outline very general care in separate paragraphs for both adults and larvae for live pet rhino beetles.
Humidity
Adults: A female will only lay eggs in a substrate that is somewhat moist. Both males and females will benefit by the availability of a wet substrate. Aside from buffering the air in the tank through evaporation, the beetles will take advantage of minimum of 4 inches of substrate to burrow in. This prevents them from drying out too much. Interestingly, the elytra and pronotum (abdominal and thoracic portions of the "shell") will darken when the humidity is high. This is good on an occasional basis, but there shouldn't be so much humidity in the tank that condensation is forming on the tank walls or lid on any regular basis. If it is, increase ventilation by adding air holes in the cage.
Larvae can tolerate dry soil for a few weeks or more with no apparent issues, but optimal growth and feeding requires moisture.
Housing/Habitats
Adults: The size of the tank does not matter for your adult pet rhino beetles. It should, however, have a substrate. If you want your adult female to lay eggs, the substrate should be composed primarily of compost soil (or top soil) about 8+ inches deep. A substrate isn't necessary, but a moist substrate does help to buffer humidity in the cage and the fastest killer of rhino beetles is a cage too dry! If you just want to observe them, you don't really need a substrate, but it will probably shorten their lifespan significantly. Rhino beetles like to burrow during the day (both US Dynastes spp.). The Eastern D. tityus also go through an overwintering period and remain burrowed both night and day, during this time.
Larvae go through three stages: L1, L2 and L3 (larval instars). Then they build a pupal cell out of dirt and oral secretions and shed again to become a pupa. It is during this phase that you can see the adult beetle is finally taking shape. The larval period, from the time the egg hatches, until the adult (US Dynastes) emerges takes 12-18 months for D. tityus and 24-36 for Dynastes granti. These numbers can vary, but the ranges are generally accurate. Larvae require a compost soil base with plenty of rotting wood from hardwood trees (oak, for example). They will make nutritional use out of softer types of hardwood wood, decaying leaves and even the soil itself. They'll pass most of this through their gut, gleaning whatever nutrition they can. As your substrate is replaced by oblong pellets, you will want to add more of the unprocessed ingredients. All these components will ideally be heat-treated or cold-treated. Baking in the oven, microwaving or freezing substrate are recommended to kill any potential hiding pests (children, please ask an adult for help). The size of the container for larvae depends on their size. An L1 larva can be kept in less than a cup of substrate, while a 32 ounce deli cup is really pushing the limits as a minimum sized container for an L3 larva. Generally, bigger is better, though it is easier to observe the progress of your larva if you keep it in a reasonably small container.
The cages for both larvae and adults should have minimal ventilation, especially for the former.
There are a number of pests that prey on the eggs of rhino beetles, but these are relatively rare in captive bred beetles. Below are three videos of Dynastes granti egg mites. If you see any "pests" in the soil, it is immediately time to start rescuing all the eggs by moving them to a new substrate. The first video shows how plump a single mite can get as it feeds on the egg. The second video shows babies that the adult mite had spawned. The third video, fortunately, shows that the egg hatched just before the baby mites began to attack the egg. The fourth video shows parasitic nematodes and the damage they cause internally to the egg.
Temperature
Room temperature is fine for both adults and larvae. Slightly warmer temperatures may help speed growth. Eggs can take 30 (D. tityus) to 90+ (D. granti) days to hatch at room temperatures. Warmer temps will shorten the span, while cooler temps will prolong hatching for many months.
The overwintering period for captive bred Dynastes tityus can be broken by exposure to room temperature for a few months. Warmer temperatures may decrease the "overwintering period".
Food
Adult beetles are tree sap feeders, but eat apple and/or banana in captivity. Watered down maple syrup, brown sugar or other sugary liquids can be offered in shallow cups (milk caps, for example), alternatively or exclusively. Fruit has a tendency to mold or attract flies. Liquids tend to dry up. Many hobbyists prefer to use beetle jelly products. That's it! Very simple.
Larvae eat rotting wood and leaves as discussed in the housing/substrate section above. Many keepers supplement the diets of the beetle larvae with dried dog food pellets. Protein supplementation helps to grow big beetles!