Bug FAQWool Sower Gall Wasp
Callirhytis seminator · Order: Hymenoptera · Family: Cynipidae
Adult wool sower wasps are tiny, about a tenth of an inch long and dark brown in color. The larvae are white, plump, and legless, living inside a round, white gall on white oak trees in spring.
Source: Wikipedia
How to recognize it
Adults are dark brown and about 1/8 inch long. Larvae are white, fat, and have no legs.
Source: Wikipedia
Size
The adult wasps measure roughly one-eighth of an inch.
Source: Wikipedia
Does it bite or sting?
These wasps neither bite nor sting people.
Source: Wikipedia
Where it lives
They lay eggs only on white oak trees during the spring. Eggs are deposited in a round, white gall that looks like a cotton ball.
Source: Wikipedia
What it eats
The larvae feed and develop inside the gall they create.
Source: Wikipedia
Life cycle
Gall wasps have a two-generation cycle: one generation makes stem galls, and its offspring lay eggs in leaf galls. The wasps emerging from leaf galls then mature and produce stem galls.
Source: Wikipedia
When you see it
Egg-laying occurs in the spring on white oak trees.
Source: Wikipedia
Where it comes from
Callirhytis seminator belongs to the gall-wasp family Cynipidae.
Source: Wikipedia
Where it is found in the US
Recorded in 42 of 51 states and DC. Most records: California, Virginia, Massachusetts, North Carolina, Texas, Ohio, Georgia, New York.
Darker = more records. Counts are museum and citizen-science records, not population size.
Source: GBIF
Status: native in North America; native in United States; native in Canada. Source: iNaturalist
Months it is reported in the US
Source: GBIF
More photos
Questions people ask
Do they damage oak trees?
No, they are not present in numbers that damage white oak trees.
Source: Wikipedia
What do the larvae look like?
The larvae are white, plump, and legless, living inside the gall.
Source: Wikipedia
Same family (Cynipidae)
Sources
- Wikipedia: https://en.wikipedia.org/wiki/Callirhytis_seminator
Look it up elsewhere: GBIF · iNaturalist · BugGuide · Wikipedia
Text written 2026-10-22 from the sources above and checked sentence by sentence against them. Data fetched 2026-10-22.