Dead stem of nipplewort, Lapsana communis, inhabited by the "pumpkin worms"

When I came across it this stem was originally 3-4x as long, and still rooted in the ground, standing upright. I got curious when I noticed that the otherwise hollow stem had little bits of processed plant material inside it, adhering to the inner wall of the stem -- suggesting the presence of an internally feeding insect. Also, the truncated top end of the stem had been mysteriously sealed with a thin layer of something that appeared suspiciously like the work of an insect. I began splitting the stem open from the top down, discarding the split-open stem pieces as I went. I found nothing alive inside the stem until I got to the spot where the blue arrow is in this photo, where the larvae were dwelling. I stopped splitting open the stem at that point so as not to further disturb the animals in their home.

Almost immediately, the larvae got to work sealing off the new upper end of the hollow stem (the part to the right of the blue arrow). The result is visible in the final two images of this series. I observed similar behavior by a sciarid larva inside an Equisetum plant this fall, and would liken this behavior to the way that caterpillars seal any entrances to their shelters with silk and/or frass. In the sciarids' case, the sealant is slime -- along with little bits of processed stem material. Until this fall I was unaware that sciarids did this sort of thing, so I decided to spend a little time documenting it.