Acorn Weevil Grubs

2013 October 16

Rosie likes to collect acorns, and had brought a bucket of them in the house on October 7, 2012. And while Sam was looking them over, she somehow broke one of them (I think she dropped it on the floor). And inside, there were several of these fat little white grubs.

They had completely hollowed out the nut, which would have been a bit of a surprise to any squirrel that might have collected it. These are about as featureless as grubs get, just a brown head and a bag-like white body.

They didn’t have any legs as far as I could see, and they moved by a combination of dragging themselves forwards with their jaws, and pushing themselves with the tips of their tails. It wasn’t fast, but they could at least progress that way.

These are clearly some sort of Acorn Weevil, in the genus Curculio. And if acorns were edible to humans, they’d be quite a pest[1]. But, since acorns taste nasty because of all the tannins in them, these particular beetles are only pests as far as squirrels are concerned. Actually, maybe not even then. The squirrels are probably perfectly happy to eat the grubs, too[2].

I tried to raise them up to see exactly which kind of acorn weevil they were, but failed miserably because I didn’t understand the conditions they needed. It seems that they bore out of the nut and burrow into moist leaf litter to pupate, and I didn’t provide them with the moist leaf litter. This suggest that the standard conditions for raising insects that emerge from nuts, fruits, or galls should probably be a tallish jar with a layer of moist soil covered by appropriate leaf litter.

[1] There is a similar grub that infests hickory nuts, which are edible. Sandy’s parents have some hickory trees, and the last time we helped them shelling the nuts, we found about one nut in 20 that had a grub similar to this in it.

[2] Actually, if these grubs don’t concentrate the tannins from the acorns, they might actually be pretty tasty if stir-fried with rice. In which case, they could be useful for making acorns edible.

4 Responses leave one →
  1. October 16, 2013

    The leaf litter stands to reason as the acorns would be on the ground when the critters emerged. Next year, perhaps?

  2. Carole permalink
    October 16, 2013

    Have found them before in red oak acorns. I wonder at what point their eggs are laid in the acorn and by what. Is it when the acorn is first forming or when it is on the ground. I seem to recall that the ones I found were collected in the fall and emerged from the acorn shortly after collection.
    The white acorns would be eaten in the fall by the squirrels, but the red would be buried for next year. Would the acorn be helping the grub by burying it?

  3. BioBob permalink
    October 21, 2013

    Acorns have been human food for millenia. Acorns just need to be prepared to remove the tannins (tannins are there to minimize animal feeding = biowarfare)

    recipes & techniques here:

  4. Sarah D. permalink
    October 11, 2014

    I am so glad to have found this post! I found three grubs moving slowly on my dining room floor after I cleaned and wondered what they were – must have come from a bag of acorns I collected in Michigan (I am in Chicago) last weekend. Problem is, I only found three grubs. Does that mean there are more somewhere??

    There were none in the bag itself, but I haven’t examined everything that may have come in contact with the bag while it was in the apartment.
    Thanks for all of the information!

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