Bug FAQTwo-horned Gall Wasp
Dryocosmus dubiosus
After hatching, the larvae cause the oak leaf to form a gall that looks like a pair of bull’s horns.
Source: Wikipedia
How to recognize it
Adults lay eggs on oak leaves and catkins, especially on coast live oak and interior live oak.
Source: Wikipedia
Is it a pest in the house?
Leaf-galling damage from this wasp is often mistaken for fungal blight or beetle injury.
Source: Wikipedia
How to get rid of it
UC Integrated Pest Management notes the damage is frequently misidentified as fungal or beetle damage.
Source: Wikipedia
Where it lives
It creates galls on oak trees throughout California in North America.
Source: Wikipedia
What it eats
The wasp uses the leaves and catkins of coast live oak and interior live oak for oviposition.
Source: Wikipedia
Life cycle
Eggs hatch into larvae that induce a horn-shaped gall on the oak leaf.
Source: Wikipedia
Where it comes from
It is native to California in North America.
Source: Wikipedia
Lookalikes
The gall damage can be confused with oak twig blight fungi and oak twig-girdling beetles.
Source: Wikipedia
Where it is found in the US
Recorded in 2 of 51 states and DC. Most records: California, Oregon.
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 does the gall look like?
The gall resembles a pair of bull’s horns on the oak leaf.
Source: Wikipedia
Which oaks does it affect?
It oviposits on coast live oak and interior live oak leaves and catkins.
Source: Wikipedia
How can I tell its damage from other problems?
The horn-shaped leaf galls are distinct, though they are often confused with fungal blight or oak twig-girdling beetles.
Source: Wikipedia
Sources
- Wikipedia: https://en.wikipedia.org/wiki/Dryocosmus_dubiosus
Look it up elsewhere: iNaturalist · BugGuide · Wikipedia
Text written 2026-10-24 from the sources above and checked sentence by sentence against them. Data fetched 2026-10-24.