Monday, March 12, 2012

Rhinoceros Beetle Grubs

Warning: This post contains graphic pictures of very large insects. Bug-phobic people should look away.

Look what Daniel found while pulling the dead English Ivy off the oak trees in the front! (The English ivy probably died in the drought, and good riddance too, since it's an invasive species and was smothering those trees.) These gigantic grubs are larval Rhinoceros Beetles. This is another one of those somewhat-tropical species that reach the northermost limit of their range here in Central Texas (and elsewhere in the southern U.S.). Texas has a few species from the rhinoceros beetle subfamily (Dynastinae, a subfamily of the scarab beetle family), and while ours aren't as impressive as some of the truly tropical ones, these beetles are still MUCH BIGGER than any other beetles we have around here.

Digging around in the thick accumulation of leaf litter under the trees just yielded more and more grubs. Daniel ended up pulling out eight of them, and we're sure there were even more in there.

He ended up relocating them to a different pile of leaves, so they wouldn't get stepped on and squished. Lucky for them Bear Grylls isn't around! He'd have a feast! I admit, while insects don't gross me out as much as some people, I'm still pretty grossed out by insect larvae. Something about how soft and squishy and squirmy they are. I think it's because they remind me of maggots, so even the larvae of other species (like even butterfly larvae) gross me out by association. So even though I know these guys are completely harmless (though I guess maggots are too), I let Daniel go ahead and dig them up and carry them around himself, and didn't help out.

Though, on whether or not rhino beetles are harmless, I'm actually finding conflicting reports. These guys are probably Ox Beetles, Strategus aloeus, because that's the only species of rhino beetle I've ever actually seen in person around here, though theoretically we could also get some Eastern Hercules Beetles (which I more commonly hear called "unicorn beetles"), Dynastes tityus, which are even more impressive. Daniel said he's seen a couple of unicorn beetles around, and found a dead one he has pinned in his bug collection (don't worry, he only collects already-dead bugs). Most people around here just call the Ox Beetles "rhinoceros beetles", even though technically they're just one certain species of rhino beetle, probably because they're the most common one.

According to Howard Garrett's Texas Bug Book (which is a good book, by the way), rhinoceros beetles are harmless detritivores that live in gardener's compost piles. He even has a picture of one on the cover! Texas A&M also says they're "Not generally considered a pest." However, Wikipedia says they're a pest and eat plant roots.

Well, I guess that just shows you that you can't believe everything Wikipedia says. I think I should trust Texas A&M. So far the only rhino beetle grubs I've ever seen have been in my compost pile, or in piles of rotting leaves like these. Even if they do eat a few live plant roots, which I seriously doubt, the adults are just so darn cool looking, that I wouldn't kill them anyway. So I hope these guys make it, and this summer I get to see some adult Ox Beetles marching around.

16 comments:

  1. wow! Cool! I saw some of these in the more out of the way corner of my compost heap last year and though I usually feed grubs to my chickens, these were so big that I just couldn't bear it, and put them gently back under some leaves behind my shed. I'm glad to know what they were, because they kind of freaked me out, to be honest.

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  2. Greg, I'm glad this post was informative, then. I suspect most people, if they found GIANT GRUBS anywhere, would be a bit freaked out. Just trying to get the word out that they're harmless and actually kind of cool. I think rhino beetles are a bit cute in a way, at least as adults, once you get over how big they are.

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  3. This is kind of unrelated, but do you have any suggestions on how to ID grass? I have some bunching grass growing in my yard that I want to know whether to keep or kill.

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  4. Grasses are really hard to identify. Usually you can only tell from looking at the seedhead, which isn't always there, and wouldn't be at this time of year.

    IMO, the main must-kill grass in Texas would be Bermuda grass, which is not a bunchgrass. I would kill that on sight, but other grass I would leave alone until I'm sure what it is. It could be Johnsongrass or KR bluestem, which are invasive and should be killed, or it could be any number of native grasses.

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  5. I found several in my compost pile today and am thrilled. If the skunks that live under the shed find them, I'm sure they'll be thrilled too! I live in Celina, TX

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  6. I think it was/is 'Texas Wintergrass', based on the long, sharp, spear like seeds it produced and subsequently put in my shoes and socks.

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  7. Greg, sounds like you're right. It's also known as "speargrass" for obvious reasons. If the spears really bother you, you can try mowing it from now on before it gets a chance to go to seed.

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  8. Hi Amanda! My apologies, I tried to find a separate way to contact you but did not find one. I'm looking to buy some rhinocerous beetles, any chance you can help me? I've had some as a pet when I was a child, and would love to have some again.

    I'm freddiefaithkeller@gmail.com

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  9. Hi Freddie,

    Sorry, I don't know where you can buy them. I think I've heard of keeping them as a pet, but I haven't seen them for sale anywhere.

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  10. I'll have to disagree about rhinoceros beetle larvae being a benign insect. I had to tear out my vegetable garden because the plants were not doing well. They were yellowing, not thriving and the fruits were underdeveloped and distorted. When I dug up the plants, the soil around the roots were full of rhinoceros beetle grubs and the roots had been destroyed. I live in central Texas.

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    1. Another possibility is that your plants were dying from something else, and the rhino beetles then moved in to eat the decaying plants. The rhino beetles pictured above were around a bunch of dead English ivy vines, but the vines were killed by drought, and then the rhino beetles, being scavengers, showed up to eat their rotting roots. They appear to prefer dead plant material rather than living.

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  11. They actually are a pest. If you have a very common plant they feed on then there isn't any significant problem from them. Places like Guam though are risking their Coconut trees becoming endangered because of their rhino beetles. So it really depends on the ecosystem they're a part of.

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  12. They actually are a pest. If you have a very common plant they feed on then there isn't any significant problem from them. Places like Guam though are risking their Coconut trees becoming endangered because of their rhino beetles. So it really depends on the ecosystem they're a part of.

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  14. These have been the only persistent pest I have in my garden. They have destrpyed the stems of all my squash. All the plants that were killed had large Rhino Beetle holes nearby. The test of my garden is thriving and in full bloom- as was my squash before those holes appeared.

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