One afternoon last week I came home from work, and when I got out of the car I found it had already accumulated a large number of wriggling white larvae, which were dropping onto it from the white pine tree overhead. This exact thing had happened on May 24 last year, and I was expecting it this time around because I knew it would coincide with the week that I’m sneezing from all the pine pollen filling the air. The ~4 mm larvae appear pretty much featureless to the naked eye, but under magnification you can see that they have six legs and a round head with two eye spots and a pair of short antennae.
Last year I dropped a number of them into a jar of soil to try and raise them, and they immediately burrowed down into it and disappeared. Nothing has emerged, but I’m pretty sure they are sawflies in the genus Xyela (Xyelidae). I first became aware of their life cycle early last April when I started seeing the adults in and around the house. I posted this photo (taken April 6) on BugGuide…
…and when it was identified to genus I read up and learned that the larvae develop in the male (pollen-producing) cones of pines. After feeding for two or three weeks, they drop to the ground, burrow down, and wait there through the winter before pupating. Adults emerge in early spring, mate, and females lay eggs in the developing cones. On April 17 this year, I took the photo below of an adult (4 mm long, like the larvae) showing off her ovipositor below the very same tree from which I’ve seen the larvae raining down.
Added 9/29/2013: Sawfly specialist Dave Smith has just confirmed that these are Xyela larvae.