This is the first in what I expect to be a series of posts highlighting commonly observed mystery leaf mines. My hope is that people will keep an eye out for them and collect any occupied ones so that adult insects can be reared and we can put names to them. You can click on any of the images below to get to the original observations. These are all mines of some unknown agromyzid fly on Pacific hound's tongue (Adelinia grande); they have been found in several California counties. Empty mines have been found as early as March 9; no one has yet found ones that clearly have larvae inside, although some photos taken in late May show small and fresh-looking mines, so there may be two generations per year.

@sea-kangaroo, San Mateo Co., CA, 3/9/2018, 5/29/2019, 6/10/2020


@temminicki, San Mateo Co., CA, 3/11/2018


@merav, Santa Clara Co., CA, 3/14/2021


@debkccb, San Mateo Co., CA, 3/15/2020


@u_phantasticus, San Mateo Co., CA, 3/20/2020


@chloe_and_trevor, Marin Co., CA, 3/31/2021, 4/22/2021


@cmaci, San Mateo Co., CA, 4/4/2020


@zufi, San Mateo Co., CA, 4/9/2021


@selwynq, San Mateo Co., CA, 4/11/2021


@elonicera, Santa Clara Co., CA, 4/14/2021


@melanopygus, Marin Co., CA, 4/29/2018


@leslie_flint, San Mateo Co., CA, 4/30/2021, 5/4/2020


@gyrrlfalcon, San Mateo Co., CA, 4/16/2021, 5/4/2020, 6/5/2020


@leptonia, Santa Cruz Co., CA, 5/10/2017


@owicki, Santa Clara Co., CA, 5/11/2020


@kzias, San Mateo Co., CA, 5/24/2020


@hoechsle, Santa Cruz Co., CA, 5/30/2019


@calloohcallay, San Mateo Co., CA, 5/30/2020


Update, 3/11/2022: People have found some occupied mines in 2022!


@gina-barton, Santa Clara Co., CA, 3/5/2022


Having seen this puparium that @nancyasquith got from one of these mines (Santa Clara Co., CA, 3/10/2022), I'm now reasonably sure this is an Agromyza species.