Tuesday, January 8, 2013

Composting with Grubs

In the past, I collected worms from different locations in and out of Tucson and dispersed them into my watered garden. After multiple attempts to start a worm colony in my soil, I have very rarely seen worms, even when watering my garden in the off-season. Without the aid of worms, what living organisms do I discover when I dig in the ground and in my compost? Grubs, of course.

Japanese June Beetle Grub

Because grubs can often eat away at roots, causing havoc to seedlings as well as damaging root crops, my previous tendency was to dispose of them by throwing them violently against a wall. However, because my children have taken the time to spare the lives of some fortunate grubs in buckets, I have experienced a recent change of heart.

Adult Japanese June Beetle

My change of heart transpired while I was upset at my daughter for putting my valuable compost into the grub buckets. As this blog is not devoted to my irrational behavior, I will just note that I need to make a mental impression to not be so quick to judgment. I suppose this is one example of why my wife keeps reminding me of this attribute I need to develop. In any case, once my initial anger about the compost subsided I quickly realized that she had not put any compost into the buckets. Instead, the rhinoceros beetle grubs had eaten away at the wood chips provided for them and turned it into rich compost.

Perhaps grubs can be useful after all.

Inside of Grub bucket - where the compost happens

Compost from Grubs

I am continuing to experiment with grubs to determine what environment suits them best, but so far I have learned the following:

1. Larger grubs are easier to work with. I can sift out the compost and leave the grubs if the grubs are larger.

2. Different varieties of beetle require a different diet in their composting environment. The large green Japanese fruit beetles prefer bedding with more nitrogen-rich foods (such as wood chips) while the very large rhinoceros beetle grubs prefer bedding that consists of more carbon-rich foods (such as horse manure).

Rhinoceros Beetle Grubs - Pretty gross!

An adult Rhinoceros Beetle

Should I learn any additional information concerning the rearing of grubs for compost purposes, I will gladly add it to this post.

If worms don't work - try Composting with Grubs!


  1. Interesting...although my grubs are the mundane not very useful Japanese beetles that don't seem to eat compost...although I may be tempted to see if they might...but I really hate the grubs...

    1. I don't care much for the grubs either, but they can make good compost relatively quickly. They also tend to be more resilient to the extreme fluctuations in temperature and moisture in my climate than worms are. For the most part my worms just don't last.

  2. I never thought myself lucky for having worms in my soil, but I certainly do now. I hope your daughter has forgiven you.

    1. Yes - worms are a great thing. My daughter did not even know I was upset at her - though it does go to show how easy it is for me to jump to conclusions.

  3. FYI- Your "Adult Japanese June Beetle" is more likely the Green Fig Beetle (Figeater Beetle/ Green Fruit Beetle) - Cotinis mutabilis, esp. in Tucson :)
    The grubs can grow up to 2 inches in length!
    And they ARE nice composters... Good to know.
    My ducks also love them both in grub and adult form!
    Thank you for your post, it actually helped me figure out what they are because I, too, live in Tucson and have been wondering about them for a while. Now I know they are nothing to worry about and I will probably stop throwing so many grubs to the ducks...
    At least the ones in the compost pile can stay in large numbers... I'll only keep a few in the garden for now...
    Thank you again :)

    1. Dear Tpark,

      Thank you so much for your comment.

      In my experience both types of beetle grubs mentioned in my post will damage vegetable roots if they run short of the compost types that they feed on. As mentioned in the post, the green beetles are able to tolerate and prefer to eat more nitrogen-rich compost while the brown beetles mentioned in my post prefer more carbon-rich compost.

      As the potential to damage and destroy vegetable roots is not only possible, but very likely, I would never allow any of these beetle varieties to live in garden itself.


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