Insect egg ball
July 31, 2009
I keep finding these egg balls under an oak tree in my yard. Can you tell me what comes out of these? (The second picture shows their exits.) The wall material is paper thin and very brittle. They are about the size of a golf ball, beige, and bumpy.
This is the Gall or Oak Apple formed by some species of Gall Wasp, a tiny wasp in the family Cynipidae. The larval Gall Wasp creates the Gall as part of its growth process and the Galls do not harm the trees. There are numerous species and according to BugGuide: “Many different cynipid wasps form large, spherical galls on oak leaves, some of which are called “oak apples.” As with most galls, ID requires knowing the species of oak. It is also critical to look at the internal structure: Even then, there are some very similar ones, and it may be necessary to examine the adult wasp that emerges.” A British Website has a photo that matches your Gall, and it is identified as Biorhiza pallida, but we believe your new world species is not the same. According to BugGuide there are “Over 750 species in North America in 49 genera” and “Small to minute, usually black, with characteristic shape: the abdomen is oval and somewhat compressed and shiny, the second tergum covers a good part of the abdomen. Each species makes a characteristic gall on a specific part of the plant. Many make galls on oaks. Most have a complex life cycle with a parthenogenetic generation and a sexual one. Each generation makes galls of a different appearance and on different parts of the plant.“ The recognized expert in this family is Charles Kinsey who died about 50 years ago after achieving worldwide fame for his studies of male and female sexuality.