Growing larger and larger Hercules beetle is the goal of many Hercules beetle enthusiasts. The largest known Hercules beetle is 181 mm (~7.1″) in length, recorded in 2018. It broke the record of 171 mm (~6.7″) set in 2015. It is a norm for enthusiasts to breed Hercules beetles at least 160 mm (6.3″). For amateurs, even 6″ is a difficult target. 

I have gathered information from different beetle keepers and consolidated them in this guide, hoping to help anyone beginners who want to make their Hercules beetles larger. Note that this is an extension to the Hercules beetle keeping guide which can be found here.

To grow bigger Hercules beetles, get the beetles from renown breeders. They are selected to grow larger and stronger. Through selective breeding, you can further enlarge the size of your beetles. Of course, you need to provide sufficient food and big-enough housing for the beetles.

Continue reading to learn more.

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Genetics play a big part in the size of beetles. There are different breeds of beetles, just like there are different breeds of cats or dogs. One of the most notable breeds is the HirokA breed by Hirofumi Kawano, who holds the record for longest Hercules beetle in 2015. 

If you have the budget, buy those well-known breeds from a reliable seller. Those breeds are specifically selected by breeders for a few generations to achieve desirable size. Here’s a comparison table between specifically selected breed and unknown breed

FeaturesSpecifically selected breedUnknown breed/Wild breed
PriceCan be very expensiveCheap
Average sizeBiggerSmaller
Egg hatch rateHigherLower
Overall survivorshipHigherLower
Genetic variationLowHigh
Differences between a specifically selected breed vs unknown breed/wild breed

Start Your Own Breed

Whether you buy a known breed or a random breed, most probably you will start your own breed so that you don’t have to buy more beetles. If you intend to breed a larger Hercules beetle, you will need to selectively breed your beetles.

To do that, select the biggest male and biggest female. Make sure your beetles are 1 month old but not more than 2 months. This will improve the successful rate of reproduction. The first generation of your breed is called the P or F0 generation and their brood is known as the F1 generation.

Similarly, let the biggest male and female from your F1 generation breed, and repeat this for every generation. After 4 generations of inbreeding – which takes around 6-8 years, you should notice the average size of your F4 beetles is significantly bigger than the F0 generation.

Hercules beetles mating. Photo courtesy: @fitness_beetleshk

There are 2 risks of inbreeding that you need to be aware of. Inbreds have very low genetic variation, which means they are very similar to each other. This directly translates to having the same weaknesses. Secondly, they have serious defects over multiple generations of inbreeding. This is because inbreeding eliminates heterozygosity and hence increases the chance of expressing deleterious recessive alleles, which is usually suppressed in a heterozygous population. An example of disease caused by deleterious recessive alleles in humans is cystic fibrosis.

If you ever make it F7 or beyond, crossbreed your F7 generation with a wild Hercules beetle or a Hercules beetle of another breed. This will increase the genetic variation of beetles and make them fitter. However, the resulting offspring might be slightly smaller since the genetic composition determining the size of the beetle is diluted. 


Putting genetic factors aside, food is another important factor to make your beetles bigger. The size of the adult beetle is affected by the nutrients consumed by the grubs. Make sure you provide sufficient food to the grub and replenish the food when it gets lesser.

The grubs feed on rotten hardwoods. The simplest way to feed them is to use flake soil. This can be bought from the same place where you buy your beetles. There are different brands of flake soil available in the market. Many enthusiasts said that different brands do not make quantifiable differences in terms of performance. 

A consistent supply chain is more important than the brand itself. It is important to make sure you do not change to a different type of substrate in the middle of growing the grubs. The grub has already gotten used to the properties of the substrate you initially put him into, changing of substrates may stress them and even kill them. Hence, buy from someone that can consistently supply the same flake soil.

Because Hercules beetles do not grow in size once they reach adulthood, it is imperative to provide them with enough food so that they can lay healthy eggs. If you are using beetle jelly, replenish the jelly once the beetles finish it. In Japan, many beetle keepers mix some proteins into the jelly, which allegedly improves the fitness of offspring produced. 

Housing of Grubs

To make the grubs grow bigger, you need to give them a bigger house. While the 3rd instar male grub can be kept in a 1 gal (~5 L) container, you should provide it with a 4-8 gal (~20-40 L) container since your objective is to let them grow bigger. The beetles cannot grow bigger if there is not enough space for them to grow! A 1 gal (~5 L) container is big enough for a female grub. 

Always keep the grub singly in 1 container. Putting the grubs together in the same container will always result in smaller adults. As mentioned in another post, keep some grubs in the same container in case the growth rate of the male and female beetles are out of sync – the male beetles may emerge after the female beetles died. This will wipe out your whole collection and you definitely want to have a back up plan.