I go to cemeteries a lot but not on Memorial Day. I don't go to the mall on Black Friday, either. Avoiding congestion, and just needing to lay low, I hung out at my apartment all this beautiful, meaningful holiday. As it turned out, the excitement was right out the front door in the courtyard. My apartment door is overtopped by a very large Siberian Elm. Sometime in the early 2000s many of the Siberian Elms along the Front Range became chronically infested with a leafminer previously only commonly seen in American Elm. This insect is the Elm Leafminer (Kaliofenusa ulmi), which is an introduced (from Europe) type of sawfly. "Sawflies" are actually wasps. Elm Leafminers overwinter as full-grown larvae within cocoons in the soil which pupate in late winter and emerge as small, bluish-black, adult wasps in spring. Adult females mate and lay eggs on new elm leaves. The larvae, sometimes several per leaf, feed between the upper and lower layers of the leaf and construct diagonal mines that radiate out toward the leaf margin bounded by major side veins from the central long-axis vein. 
After feeding within the brown mines, the larvae bail from the tree crown and drop to the ground where they burrow into the upper soil to pupate. Well, the last few days since the snow melted and the rain stopped have been peak larval bailing from leaves days. The 2-3mm pale yellow larvae are raining from the sky, and all over my sidewalk and bare places in the lawn. 
[This insect is covered briefly in "Colorado Birds" volume 50(3) in "The Hungry Bird" column titled "Breakfast At Jane's"]. To put it mildly, the birds were responding today. Here is a summary of what I saw feeding on Elm Leafminer larvae in my courtyard about a mile east of the CSU campus. Those species preceded by an "X" were pulling them out of leaf mines. Those preceded by a "#" were nipping them off the ground and sidewalk.
X Swainson's Thrush (at least 3)
X Dusky Flycatcher (repeatedly went down to the ground from low perches)
X Common Grackle
X American Robin (several)
# Red-breasted Nuthatch
# Lazuli Bunting (at least 5) see photo, note larvae visible within the pale mined portions of leaves at 4 and 6 o'clock from the bunting's beak.
# Black-headed Grosbeak
# Black-capped Chickadee (2)
# Western Tanager
# Yellow Warbler
# American Goldfinch
# Warbling Vireo
# Downy Woodpecker (see photo, which shows larva pulled from within a tan leaf mine on the bird's beak tip)
Total species seen in the yard today: 27 (probably a high count for the 20+ years I've lived here)
Dave Leatherman
Fort Collins
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