Question of the Week – Number 2: April 7, 2022

Aaron Goodwin of the Tulsa Zoo shows us the very large size of grubs of eastern Hercules beetles.

“In digging in my compost pile and garden I’ve unearthed several very large grub worms – much larger than any I’ve found in my yard. Do I need to treat for them? When and with what?”

I had this question several times this past weekend so I thought it might be worth mentioning. These grubs are, compared to the ones you’re used to seeing, huge! I’ve encountered them 8 or 10 times myself in my own gardens.

The adult male eastern Hercules beetle has horns used in fighting off other males in the time of mating. These are harmless to humans, however. These adults can reach sizes of more than 2 inches in length. Photo by Steve Thomas from TAMU Web page in link below.

These are the larvae of the eastern Hercules beetle. I learned it a long time ago as the “rhinoceros” beetle, so named for obvious reasons.

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The good news is that this insect, in both its larval and adult forms, is harmless to adults and our plants. The “horns” are used by the males in battles during mating. And the larvae feed off decaying organic matter, not living roots like the white grubs of our common June beetles.

Here is information on the eastern Hercules beetle from Texas A&M.

And here is information on the damaging white grub of the June beetle, also from Texas A&M entomologists.

This is the far more common (and much smaller) June beetle. Both photos are from TAMU publication in link above.
Although much smaller than the larvae of rhinoceros beetles, June beetle larvae are the ones that can do millions of dollars of damage to Texas lawns in late summer and fall. The publication linked above walks you through how to recognize their damage and check for their presence, also how and when to slow their impact on turf when necessary.
Posted by Neil Sperry
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