|Why not just one?|
Recently I’ve been blogging about my travels, but it’s time to take a short break because here at home, things are happening! A tree is in leaf (more about this next week) and midges have emerged. Maybe.
Last March I wrote a post about the cones that are so common on willows along the Laramie River. Of course they’re not really cones. They’re galls that are shaped like pine cones. And wouldn’t you know it – they’re called pinecone willow galls and are caused by the pinecone willow gall midge, Rhabdophaga strobiloides, a tiny fly.
The midge lays an egg in a terminal bud, and the egg and the larva that hatches release a chemical causing the plant to grow numerous small overlapping leaves – the “cone”. The larva matures inside for about a year, and then metamorphoses into a midge which emerges and flies away to repeat the cycle.
Pinecone willow gall.
Galls are common on willows along the Laramie River. Some plants have many, others none.
I picked an especially plump gall (above) thinking it was more likely to have a midge developing inside, and put it in a loosely capped jar before I left town. Four weeks later there were four tiny dead flies, all the same kind, in the bottom of the jar. I was excited! They looked like the gall midges I found online:
Gall midges, family Cecidomyiidae; probably some kind of willow gall midge (source, in part).
This one was the best preserved of the four flies I found in the jar:
Then it occurred to me: Why four flies? Why not just one? Supposedly the pinecone willow gall midge lays a single egg in a terminal bud. However, many other insects take up residence in the galls that develop – beetles, caterpillars, sawflies, wasps and other midges. In fact, in one study 564 insects were reared from 23 pinecone willow galls, and only 15 contained the original host (source). Maybe these flies were squatters.
|Looks like a gall midge, doesn't it?|
|It's the right size ... about 3 mm.|
Aarrgh. Nature confounds my nice simple stories more often than not!