"Elm Leaf Miner" Sawfly (six photos)
  Fenusa ulmi
4 mm (sawfly)
5 mm (larva)

Update:  These photos show the tiny sawflies from the first day I saw them (May 1), when I assume
 they started laying eggs, to one day 3 weeks later (May 21) when I found the larva inside a leaf. 
I took photos to show the leaf damage at 14 days and 21 days. I can only estimate how long
the process takes because I am still seeing some of these sawflies around the yard.

fenusa sawfly
These tiny sawflies were all over my Kerria japonica plant, which is in bloom and is thriving in the
shade under my blue spruce, a neighbor's crab apple tree and a 60+ foot Siberian elm, which is called
a "Chinese elm" by just about everyone in Utah.  T
here were scores of them.  [Update: and it just
hit me a few minutes ago that this is most likely the Elm Leaf Miner Sawfly because the sawflies
are directly beneath the elm - duh! Further update: when I checked the branches of the elm, they
were covered in sawflies - there must be thousands on that big elm!] Carol Davis 5-1-2014

sawfly on Kerria japonica plant

These sawflies are obviously a few weeks ahead of the ones I took photos of
in 2010 (shown below). These are non-native species.


brown wasp
Bugguide.net helped identify this as a Sawfly. The larvae wreak havoc on the leaves of elms.
The adult Sawfly merely feeds on pollen or munches on an occasional insect.  Sawflies are
not "flies" but a kind of primitive wasp. This site (Bumblebee.org) has a great description
of them along with some detailed drawings.  Carol Davis 5-21-2010


elm leaf miner sawfly damage
This photo is pretty representative of the damage I found on the leaves of this large Siberian Elm on May 14, 2014.

Fenusa ulmi sawfly damage
Just one week later:  this is major damage and the tree is actually (I believe) dying because of it.  Every year
 it looks worse. The white part of this leave is like paper and it is hollow inside where the larvae have fed. 
I saw two or three larvae wiggling around inside so I cut the leaf open and found the 1/4 inch larva below.

Fenusa ulmi larva
This little squirt could really move. As you can see from the holes in the
damaged leaf above, some of the larvae have already broken out and have
 probably fallen to the ground to start the sawfly circle of life all over again.
  Carol Davis 5-21-2014

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