I keep my Goliathus in trios, one male for two females, in clear plastic containers (the ones used to store clothes). This allows the male to successfully mate and the females to oviposit without becoming overcrowded. Although a newly active female may mate as soon as she is able to feed, she will not lay eggs for another month or two. And even once the eggs are found, I’ve found that the first batch of eggs is often not viable. A female Goliathus can lay between 30 and 50 eggs during her lifetime. Once the breeder is sure that the female is laying fertilized eggs, the male can be removed. In my experience, once the female has been fertilized, the presence of the male is no longer required. The male’s frequent advances can be a distraction, especially since he cannot run away from his mate as he would in the wild. My Goliathus are kept in clear plastic containers with their lids cut out in the shape of a window. The window screen is installed later to allow air circulation and allow light to enter. However, any old fish tank can do the job. Goliathus can often be seen among tree branches in the wild, so a vertically installed terrarium is recommended to allow for tree branches. Higher branches will allow the beetles to climb and increase the available surface space in the tank. As with other beetles, medium-sized branches should be placed in the soil of the substrate. This will allow the flipped beetles to grab onto something so they can flip up.
The substrate used in the rearing tank may be identical to that used for other Cetonidae species. The depth of the substrate necessary for a correct laying of eggs is 20-30 cm. It is very important that the last 10 cm is compacted into a very hard layer. This is the layer where the female will lay most of her eggs. Although not necessary, a log buried at the bottom seems to entice the female to lay her eggs near it. This may be a natural behavior for her to lay her eggs near tree roots in the wild. Such a location near a tree may be richer in terms of higher quality compost (which the younger larvae require) and a higher concentration of other invertebrates encountered (which the older larvae feed on).
The Goliathus egg-laying process shows similarity to Dynastidae species than to other Cetonidae. The female will lay her eggs in individual nodules made from the substrate which is very similar to how female Dynastes Hercules prepare her eggs. Flower beetles generally lay their “free-floating” eggs on the substrate as long as the substrate is in suitable condition. Unlike Dynastidae eggs, which are very shock resistant (they maintain their viability even after being dropped and bounced off the ground), Goliathus eggs are extremely fragile. Even when handled carefully, eggs can break without warning. A visual signal that oviposition has begun is the presence of vertical tunnels on the surface dug by the females. They will disappear underground for several days and re-emerge from the substrate to feed. The incubation time of the egg varies between 2 and 3 weeks. The egg will increase in size during this period. I recommend collecting eggs once a month to avoid any cannibalistic behavior. More frequent searches will increase the risk of breaking newly laid eggs. Eggs can be stored in empty film reels or, better yet, in empty, clear pill containers that can be purchased at pharmacies. The second method allows you to see the development of the egg.