Care Sheet - Neptune Rhinoceros Beetle (Dynastes neptunus)
Written by: Richard’s Inverts
An adult male Neptune Rhinoceros Beetle (Dynastes neptunus ssp. neptunus)
Common Name: Neptune Rhinoceros Beetle
Scientific Name: Dynastes neptunus
Distribution: South America
Etymology:
[Dynastes] named after the son of Heracles and Erato from Greek mythology
[neptunus] named after the Roman god of the sea
World Record Size:
Wild – ### mm
Captive Breeding – 157.3 mm (2018)
Egg to adult: 12-24 months
Adult lifespan: 3-6 months (up to 12 months in exceptional cases)
Pupal stage duration: 2-3 months
Maturation time of fresh adults: 2 months
Egg incubation duration: 1 month
Rearing temperature: Cool room temperature (18-22°C)
Distribution data of extant Dynastes neptunus subspecies:
Dynastes neptunus ssp. neptunus – Colombia, Ecuador, Peru
Dynastes neptunus ssp. rouchei – Venezuela
An mating adult pair of Neptune Rhinoceros Beetles (Dynastes neptunus ssp. neptunus)
Species Description:
Dynastes neptunus is the second largest beetle beetle in the world after the Hercules rhinoceros beetle (Dynastes hercules), and it is distributed along the western side of the Andes Mountains.
Morphologically, D. neptunus is very similar in appearance to D. hercules, but there are several key differences such as the shape and number of horns, colour, and the time of day when it is active. Unlike D. hercules, the cephalic horn (lower horn) of D. neptunus is as long as the thoracic horn (upper horn), and there are also two pairs of short horns in the front of the prothorax. The body color is fully black and shiny.
D. neptunus is typically active between 3am to dawn. which is similar to the closely related satan rhinoceros beetle (Dynastes satanas). In recent years, differences in the two distinct populations of D. neptunus (Venezuela vs. Colombia/Ecuador/Peru) have been recognised, and this species has been reclassified into two separate subspecies.
Rearing notes:
Despite being native to the tropics, Dynastes neptunus is weak to heat as it lives in the cooler, high-altitude cloud-forests instead of the warm, lowland rainforests. Therefore, rearing temperatures higher than 25°C will result in the development of weak, small adults or even death. It is highly recommended to rear and breed this species at temperatures at or below 20°C (but above 15°C) for best results.
Compared to other rhinoceros beetle species (Dynastinae), larvae of Dynastes neptunus prefer substrate at a higher level of fermentation and decay.
An adult male Neptune Rhinoceros Beetle (Dynastes neptunus ssp. neptunus)
Food for Beetle Larvae:
As with most stag beetle species (Dynastinae family), the larvae will feed on substrate that is mainly composed of decayed wood of trees in the Beech family (Fabaceae family) which include oaks (Quercus spp.), beech, (Fagus spp.) and chestnut, (Castanea spp.). A general beetle substrate guide that covers the different types of substrates for different types of beetles can be found HERE.
Unlike with stag beetle larvae, a portion of the substrate for rhino beetle larvae can be replaced with decayed leaves of the same tree species if there is a shortage of decayed wood. I recommend that the ratio of leaves should not exceed the ratio of 1:4 (20% : 80%) of leaves to wood respectively.
To raise large adults, home-made Flake Soil should be used instead of wood collected from nature. Flake Soil is the term used for fresh sawdust that has been decayed under controlled conditions with additional protein sources that results in a uniform, earthy substrate that is rich in nutrients.
To view my tried and tested flake soil recipe with a breakdown of tips and tricks, please click HERE.
Food for Adult Beetles:
Adult beetles can be fed on beetle jelly or most sweet fruits such as bananas, apples, mangos, peaches, melons and watermelons to name a few. Adult females should preferably be given fruits that are higher in protein content such as bananas to aid in their egg production.
Foods to avoid for adult beetles are certain types of sugar-water, and fruits high in acidity such as those in the Citrus genus (oranges, lemons, grapefruits, etc.). Fruits that are high in acidity are said to disrupt the pH balance in the gut of some species, potentially leading to refusal to feed after a certain period of time.
Breeding Dynastes neptunus:
How to make a breeding box:
Prepare a 50 L box and fill it 70% full with substrate.
Compress the substrate down as hard as you can (use your hands to press it from above).
Lightly fill up to 70% of the container again with substrate.
Place perches on the surface so that the adult beetles can right themselves up if they accidentally flip over.
Place fruits (or beetle jellies) on the surface as well.
Once the breeding box has been completed, place both the male and female Dynastes neptunus together in the breeding box. Leave them together for 7-10 days to ensure that they mate properly. Afterwards, the male can be taken out and kept separately if you wish.
If the male is seen attacking the female, it is a likely sign that they are not sexually mature yet. When this hapens, keep them separately in their own enclosures for a few weeks before attempting again.
How to check for eggs/larvae:
The breeding box can be checked for any eggs and larvae 1 month after the female has been introduced into the breeding box. Find a large box and empty out the substrate from the breeding box into it by flipping it over. Carefully break apart and work through the substrate in order to find the eggs and larvae. They are soft and fragile, so please take care to handle them gently when moving the eggs and larvae.
Raising the larvae:
Larvae should ideally be separated and reared individually to prevent the larvae from getting stressed out by each other (and to prevent any risk of cannibalism in more aggressive species). Communal rearing is possible, provided that plenty of space and substrate is given. Dynastes neptunus can be reared on either wood/flake soil. At the L3 stage, the larvae should be kept in a container that is a minimum of 5000 ml in size.
Pupal stage:
From the moment onwards after the larva constructs a pupal cell, it is important to keep disturbance to a minimum. Please refrain from unnecessarily picking the container up or shaking it. Their pupal period is about 1 month, after which they emerge into an adult beetle.
