Wednesday, December 5, 2012

Acorns With Holes

Warning;  My wife says, "This could be your grossest post - a worm coming out of an acorn!"
   Have you ever seen the acorn insects that make the neat little holes in acorns?   Who makes these holes?
acorn with exit holes of acorn weevil larvae (Curculio)
Well, these particular holes are exit holes from Acorn Weevil larvae (Curculio spp).
   Scroll down to see a series of pictures of an acorn weevil grub as it squeezed its fat self out through a hole in an acorn.
acorn weevil larva chewing exit hole in acorn
Acorn Weevil larvae are fat little grubs that feed on the nut inside the acorn.
acorn weevil larva
 You can see (in these two photos) evidence of the larva's tunneling in the acorn behind it.
 Notice how the grub crawls... it uses its head to lift itself, contracts its body, then drops and stretches.
grub of an acorn weevil
   More than one weevil larvae can often be found in one acorn. The larvae of some species use the same exit hole while in other species each larva make their own hole.
   This photo shows a split acorn with an acorn weevil larva that was still inside when I cut open the acorn.  Also visible is lots of frass, a bit of acorn nut meat, and perhaps some tiny, dipterous larvae.
wormy acorn
  This photo was taken a few weeks ago... I suspect I interrupted the grub's work of chewing an exit hole since they leave the acorn in the late fall to pupate in the ground.  If I would go out now and cut open some acorns I doubt I would find many weevil larvae.
  Anyway, how does that fat acorn weevil grub manage to exit the acorn through such a small hole?
acorn weevil grub chewing exit hole
 First, it chews a hole about the size of its head.
acorn weevil larva exiting acorn
 Then it begins to "worm" its way out...
acorn weevil larva emerging from acorn
The weevil larva does this by stretching its body and curling it...
 and contracting....
acorn weevil larva emerging from acorn
 and wiggling...
acorn weevil grub leaving acorn
 and swaying back and forth...
acorn weevil larva emerging from hole in acorn
 and back and forth...
 wiggling some more...
acorn weevil grub exiting hole in acorn
and squeezing...
larva of acorn weevil emerging from acorn
 and stretching and contracting...
emergent larva of acorn weevil
 Then, plop, out it comes!
emergent larva of acorn weevil
 Once the weevil larva leaves the acorn it will work its way down into the leaf litter and pupate and eventually turn into a Acorn Weevil with a long, curved snout.
Wasn't that fantastic?!?
By the way, these holes make convenient entrances and exits for various other insects.  See my next post about these acorn holes that are sealed by acorn moth caterpillars.

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