Grubosaurus Update

You always end up getting involved in things because of, you know, the strange things your life brings you into contact with.

~Edward Norton

I have had a couple of unusual “pets” these past few months. You may recall in an earlier post, I reported on receiving some orphaned Eastern Hercules Beetle grubs one day at work.

Eastern hercules beetle grubs

Eastern Hercules Beetle grubs (click photos to enlarge)

A woman brought them in after they were discovered in the hollow of a large tree she had taken down in her yard. She wasn’t sure what they were, but hoped someone at the Garden could tell her and might take them. The front desk volunteer apparently thought, Hmmm, who here would want something like this?…Oh, Mike, he probably would. And that is how I came to have two large grubs in a flower pot of rotten log and topsoil on our screen porch since late March. They are pretty easy pets to take care of – I checked them once or twice a week, spritzing the soil surface each time with a little water to prevent them from drying out. A few times over the summer, I refreshed their rotten log food supply with decayed wood and a couple of apple slices. On several occasions, I showed them to a few house guests (we have tolerant friends) and to visitors during some programs at work. The last time I did this was about two weeks ago for a group of summer camp kids. To do this, I gently poured the soil out into another bucket to reveal the grubs. On the last pour, I noticed one of the grubs had made what looked like a chamber in the soil (it was an impression in the soil about the size of a large chicken egg). I should have known what was about to happen, but it didn’t register at the time.

This past Sunday afternoon, I went out to once again spritz them with water, and when I lifted the lid off the bucket, I was amazed (and a little startled at first) at what I saw…

Eastern Hercules Beetle pupa

The alien on our porch, the pupa of an Eastern Hercules Beetle

…and it moved! It’s alive! One of the grubs transformed into a bizarre-looking pupa. This will become a male beetle, as evidenced by the horns, which apparently are quite fragile in the pupal stage. The impression I had seen in the soil a couple of weeks ago was the start of a pupation chamber. The larvae make these one to two weeks prior to pupating. I was probably lucky that my disturbance of the soil had not disrupted this transformation.

The reference I bought talked about this delicate life stage, but did not give information on how long the pupa stage lasts. Another web search found a site that summarized the life stages of the Eastern Hercules Beetle (from the University of Kentucky Critter Files on Eastern Hercules Beetles):

Adult longevity: Typically 3-6 months. The rare adult will live up to a year plus.

Egg-laying to egg hatch: 1 month

Egg hatch to pupation: 12-18 months

Pupation to emergence: 2-3 months, depending on temperature

Emergence of teneral adults to fully-formed adults: About 1 month

I am amazed at the life span of these amazing insects. It looks like I will have these pupae until December or so, when they will emerge as adult beetles. But, they apparently remain in the soil for a month or more while they harden their exoskeleton and change to the adult coloration. Stay tuned. I really want to have one of these giant beetles (with about a 6-inch wing span) flying around the house one day next spring:)


The Eastern Hercules has a wing span up to half a foot, the armor of a knight, and the spots of a leopard.

~Orin McMonigle

I guess I should be honored that the front desk volunteer thought of me first. One day a little over a week ago, I got a call saying a woman was at the front desk with something she thought the Garden might want. She had a tree company take down a large tree in her front yard and the workers had discovered some Eastern Hercules beetle (Dynastes tityus) grubs in the rotten core of the tree. They had taken most of the grubs but she later discovered some still living in the rotten stump. So, she brought them to the place she knew cares for all things natural, and asked if anyone might want to keep them. Somehow, my name came up….go figure.

Eastern hercules beetle grubs

Eastern Hercules beetle grubs (click photos to enlarge)

When I went downstairs, the lady pulled out a flower pot filled with rotting wood from the stump and shook it around to reveal two huge grubs.

Eastern hercules beetle grub

They resemble the large grubs you frequently find under logs, only much larger!

These grubs are as thick as my thumb and as long as my index finger. They resemble the large, curled beetle larvae I often find under logs, but these are much larger. The only other grubs I have seen that were this large were in the Amazon. Years ago, on a museum educator workshop, we were walking in the jungle along the river. One of our participants was a teacher from a local village. The group stopped next to a fallen tree to look at some birds in the canopy above. I noticed the local teacher leaning over the fallen tree trunk, listening. He then became very excited, ran back to his village and returned with a machete. He began to chop into the log, pausing, and listening, then chopping some more. He soon exposed a group of huge beetle grubs. He had heard them chewing inside the log and wanted to get them out as they are a prized food in that region. After explaining what they were, he proudly presented one grub to the three group leaders for us to take the first bites. Being the youngest of the three, I managed to get the back end of the larva. I can’t say I really recommend them raw (or maybe it was just the choice of my cut). On his recommendation, we took the remaining grubs back to the lodge as a side dish for dinner that night. The roasted grubs were much more palatable, with a somewhat nutty flavor.

Eastern hercules beetle grub in hand

And to think, I ate something like this once

But not to worry, I have no intention of chowing down on these grubs. My interest is purely scientific. After bringing these not-so-wee-beasties home, I started searching the web for information on how to keep them. As is often the case these days when I search for what seems like an obscure topic, I found a wealth of information, including a link to purchase a guide to rearing Eastern Hercules beetles. Well, naturally, I had to have it.

Raising Hercules Beetles guide

You never know what you will find on our bookshelf

The booklet arrived a few days later and has everything you need to know about breeding and raising these beautiful insects. Apparently, it has become a thing to raise these behemoths (or their close relatives) as pets, especially in Japan, where they are sold in many pet stores. I learned I may have my pets for awhile, as they remain larvae for 12-18 months! Based on the information in the book, I now have them in a large flower pot with some potting soil and rotten wood. The grubs feed on the decomposing wood and associated microbiota. The substrate needs to stay moist (not wet) and I will need to replenish the rotten wood from time to time and maybe enrich the substrate with some rotting fruit or dry dog food on occasion. After pupating, the adult beetles will emerge and can live for 6-12 months.

Eastern hercules beetles adults specimens

Female (left) and male (right) Eastern Hercules beetle specimens from our collection at work

I have seen the adult beetles come to lights and have found a few dead ones over the years, but had never seen the grubs until now.

Eastern hercules beetles adult male specimen

Male Eastern Hercules beetles are adorned with prominent horns

The adult males are among the largest and heaviest beetles in the United States. The horns are harmless to humans and are used for battling between rival male beetles. The spot pattern is distinctive for individual beetles. Adult beetles feed on rotting fruit and tree sap. The large horn on top has a lining of stiff  “hairs” underneath. I tried to find a purpose for this distinctive trait, but, as yet, have not found any information on it. If anyone reading this knows, please drop me a note.

Here’s hoping I can successfully raise these larvae to adulthood. In the dedication to his book on rearing these beetles, the author thanked his wife for tolerating the beetles flying around the living room. Melissa and I are both looking forward to seeing and hearing that in a few months. Stay tuned…