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Of my 6 x Chelorrhina Polyphemus grubs, 3 are now cocoon-ing. This is very exciting and my first time of experiencing keeping flower beetles and watching their full life cycle. Also a little bit nerve wracking that I don’t do anything wrong, but it’s good to know I have THE COMPLETE GUIDE TO REARING FLOWER AND JEWEL SCARABS book (note pages 19 ~ 22) and Andre of Pet Insects for his generous advice.
“It’s amazing that giant flower beetles like CHELORRHINA POLYPHEMUS can grow from egg to adult in six months while many tiny beetles from other subfamilies must spend two to five years to complete a single life cycle.” ~ The Complete Guide To Rearing Flower And Jewel Scarabs
How long does pupation last? According to the rearing book, a few weeks to a few months…which can mean anything! –> Do you sense my worry?! The same kind of worry I had when I first bravely hibernated my Hermann tortoise.
Building a pupal cell ~ Chelorrhina Polyphemus are one of the few types of flower beetle that often build their pupal cells against the sides of the container. This is very convenient and nice for us to observe them 🙂
Do not tamper! ~ I’ve made an informed decision NOT to fiddle with the cocoons. Making a tiny hole in the cocoon to observe the ever~forming beetle can result in the grub ~ if still active ~ in escaping and dying; also, if the adult beetle is removed too early from the cocoon, the new exoskeleton will not yet have hardened and the newly formed beetle is therefore quite vulnerable and has to be handled with gentle care. I say let nature run its course and the beetle will emerge when mature and ready.
However…there are times when the ever~forming beetle dies in the cocoon or pupal cell. IF the cocoon is too dry and tough the poor beetle will be trapped inside to die ~ therefore, the correct conditions are paramount to successful emergence.
Ideal Conditions ~ If moisture levels are too high the coocon walls will weaken and maybe collapse. Grubs or cocoons can rot and die. On the other hand, if the environment is too dry ~ bone~dry! ~ the beetle will be trapped inside for an untimely death. It is good to know that the strong walls of the cocoon do protect the developing beetle from the dangers of earthworms and wireworms. If the substrate was too wet, increased ventilation may help; a constant room temperature of 65~85 degrees Fahrenheit (NEVER below 65F; 70~75F optimum as 85F can lead to sickly small grubs if the food is lacking in quality); due to potential cannibalism, a separate pot for each Chelorrhina Polyphemus grub, with 10 cm of substrate; a substrate of crushed, decayed, oak leaves mixed with rotten wood and compost. Sand has been found to be beneficial in producing strong cocoons ~ particles about 1 mm in dia, a small handful as more than this can result in the beetle becoming deformed (they actually eat this!). Indeed, some types of beetle, such as the Goliathus, cannot produce cocoons without sand!
It is important to note that a high percentage of cocoon fatalities are the result of negligence whilst at L1 stage, when the grubs are very young and small (appropriate food quality and maintenance of care). Certain flower beetles need protein in their diet (dry dog biscuits; fish flakes).
T I P ~ Moisture levels: If the rearing ‘cage’ or container has a lid with few or even no ventilation holes, regular misting is not required. But NOT air~tight!
The Cocoon ~ Pupal cells or cocoons have a wall of 1~2 mm thick, but can seem thicker because of what the grub has stuck to the outside. Dry conditions = harder walls; wet conditions = flimsy, collapsable walls. Prior to building its cocoon the grub appears “squat and dumpy” (The Complete Guide To Rearing Flower And Jewel Scarabs) and must not be disturbed. A week before, the grub has busily collected, eaten the substrate in order to build the cocoon (hence the lumpy deformed appearance!). Just Right: The grub builds itself a cocoon exactly the right size and shape to accommodate its needs for molting and wing development.
Whilst cocooned, flower beetles fold their horns backwards against the head and pronotum; 2 weeks following emergence, the horns move into the normal position.
Removing the cocoon ~ The Cocoon of the Chelorrhina Polyphemus should be removed from the cage and stored horizontaly in an inch of damp substrate within a closed container to prevent desiccation, extreme dryness.
Copyright Stephanie Faith 2010
The Complete Guide To Rearing Flower And Jewel Scarabs; Andre, Pet Insects