If you cut open a goldenrod gall in fall, you’re likely to find on the inside the larvae and pupae of the gall fly. The female laid her eggs on the stem in spring. A larva from a hatched egg chewed its way into the stem, causing a golf ball-size gall to start forming and harden around the larva. No one knows just how a larva causes a gall to start, but it may have something to do with the larva’s saliva, which may mimic plant hormones.
The larva will stay in its gall the rest of the year and continue to develop. By late fall, it will be plump and ready to enter the pupal stage to develop into an adult, which will emerge next spring.
But the larva is not always safe — downy woodpeckers in winter often peck into the galls and retrieve the fat, tasty larva.
IN THE SKY: From David Dundee, Tellus Science Museum astronomer: The moon will be first quarter on Friday (Aug. 5). Rising in the east are Mercury (very low) just before dawn; Venus, a few hours before sunrise; Mars, around 2 a.m.; Jupiter, around midnight; and Saturn, a few hours after dark.
Charles Seabrook can be reached at firstname.lastname@example.org.