Bug FAQCrystalline Gall Wasp
Feron crystallinum · Order: Hymenoptera · Family: Cynipidae
The crystalline gall wasp makes small, single-chambered galls about 12 to 14 mm tall on oak leaves. Females of the sexual generation are dark black, while the asexual females are chestnut-red, and males have lighter antennae. The wasp has a complex life cycle with both bisexual and unisexual generations that appear at different times of year.
Source: Wikipedia
How to recognize it
Sexual-generation females are black and darker than males except for the antennae. Asexual-generation females have a chestnut coloration.
Source: Wikipedia
Size
Each gall is 12 to 14 mm high and about 7 mm across, with a single larval chamber.
Source: Wikipedia
Where it lives
Galls are found on all oak species throughout California. The unisexual generation forms galls on leaf undersides in fall and summer, while the bisexual generation is on leaf tops.
Source: Wikipedia
What it eats
The all-female generation creates pink, hairy galls that may be white, red, or brown.
Source: Wikipedia
Life cycle
There are several female types across generations: sexual, bisexual, asexual, and unisexual. The bisexual generation emerges in late winter and in spring makes smaller, short-haired galls.
Source: Wikipedia
When you see it
The bisexual generation appears in late winter, while the unisexual generation occurs on leaf undersides in fall and summer.
Source: Wikipedia
Where it comes from
Its galls turn up on every kind of oak in California.
Source: Wikipedia
Lookalikes
It was formerly known as Andricus crystallinus.
Source: Wikipedia
Where it is found in the US
Recorded in 48 of 51 states and DC. Most records: California, Texas, Virginia, Oregon, Florida, Massachusetts, Illinois, Ohio.
Darker = more records. Counts are museum and citizen-science records, not population size.
Source: GBIF
Status: native in North America; native in United States. Source: iNaturalist
Months it is reported in the US
Source: GBIF
More photos
Questions people ask
What trees does the crystalline gall wasp affect?
It forms galls on all oak species in California.
Source: Wikipedia
When do the different generations appear?
The bisexual generation emerges in late winter; the unisexual generation appears on leaf undersides in fall and summer.
Source: Wikipedia
What do the galls look like?
They are pink, hairy galls about 12 to 14 mm tall and 7 mm wide, with a single chamber for the larva.
Source: Wikipedia
Same family (Cynipidae)
Sources
- Wikipedia: https://en.wikipedia.org/wiki/Feron_crystallinum
Look it up elsewhere: GBIF · iNaturalist · BugGuide · Wikipedia
Text written 2026-10-23 from the sources above and checked sentence by sentence against them. Data fetched 2026-10-22.