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 mate successfully and allows the females to oviposit without feeling too crowded. Although a newly active female may mate as soon as she is able to feed, she will not lay eggs for a month or two. And even once the eggs are found, I have noticed that the first batch of eggs is often not viable. A female Goliathus can lay between 30 and 50 eggs during her life. 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 necessary. The male’s frequent advances can be distracting, especially since he cannot run away from his partner as would be the case in the wild. My Goliathus are kept in clear plastic containers with their lids cut out in the shape of a window. Subsequently, a screen is installed on the window to allow air circulation and allow light to enter. However, any old fish tank can do the job. Goliathus can often be seen amongst 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 on the substrate floor. This will allow any flipped beetle to grab onto something to flip it backwards.
The substrate used in the rearing tank can 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 are 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 deep in the bottom appears to prompt the female to lay her eggs near it. This can be a natural behavior to lay eggs near tree roots in the wild. Such a location near a tree can be richer in terms of higher quality compost (required by the younger larvae) and a higher concentration of other invertebrates found (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 their eggs. Flower beetles generally lay their eggs that are “free-floating” in the substrate as long as the substrate is in proper condition. Unlike Dynastidae eggs, which are very resistant to shocks (maintaining their viability even after falling and bouncing on the ground), Goliathus eggs are extremely fragile. Even when handled with care, eggs can break without warning. A visual sign that oviposition has begun is the presence of vertical tunnels in the surface excavated by the females. They will disappear underground for several days and will re-emerge from the substrate to feed. The incubation time of the egg varies between 2-3 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 your risk of breaking freshly laid eggs. Eggs can be stored in empty film reels or, better yet, in clear empty pill containers that you can buy at pharmacies. The second method allows you to see the development of the egg.