Andricus perditor, n. sp.
The acorns of Q. ilicifolia are, as is well known, two years in reaching maturity. In the Spring of the second year they are still very small, hardly as large as a coriander seed. At this time ants are often seen hurrying about among the young acorns and feeding upon a liquid that exudes from some of the acorns. The affected acorns are really galls--transformed acorns--that differ little in form and color from the unaffected acorns. The larva of a gall-fly lives in each of these pseud acorns. Its larval growth is complete in Spring or early Summer. I have never found them very abundant though they appear quite constantly from year to year.
”- HF Bassett: (1900) New Species of North American Cynipidae (1900)©
Reference: https://www.biodiversitylibrary.org/page/7522373#page/337/mode/1up