Bug FAQCalifornian Woolly Oak Aphid
Stegophylla essigi · Order: Hemiptera · Family: Aphididae
The California woolly oak aphid is a North American species that lives on many oak trees in California. It overwinters as eggs and produces several generations each year, with females reproducing without mating in spring and both winged and wingless males appearing in November.
Source: Wikipedia
How to recognize it
Infested oak leaves often have margins that curl upward and turn reddish.
Source: Wikipedia
Is it a pest in the house?
A sign of their presence is oak leaf margins that fold upward and become reddish.
Source: Wikipedia
Where it lives
It is found on many California oak species, including blue, valley, Oregon white, coast live, interior live, black, and scrub oaks.
Source: Wikipedia
What it eats
The aphid can reproduce parthenogenetically on evergreen oaks, especially when leaves are bound together by caterpillar silk.
Source: Wikipedia
Life cycle
It overwinters as eggs and goes through several generations each year.
Source: Wikipedia
When you see it
Both winged and wingless males, as well as oviparous females, are produced in November.
Source: Wikipedia
Where it comes from
Stegophylla essigi is native to North America.
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 Canada. Source: iNaturalist
Months it is reported in the US
Source: GBIF
More photos
Questions people ask
How can I tell if I have California woolly oak aphids?
Look for oak leaf edges that are curled upward and have a reddish color.
Source: Wikipedia
What oak trees do they live on?
They are found on many California oaks such as blue, valley, Oregon white, coast live, interior live, black, and scrub oaks.
Source: Wikipedia
When do they reproduce?
Females reproduce without mating in spring, and both winged and wingless males appear in November.
Source: Wikipedia
Same family (Aphididae)
Melon AphidAphis gossypiiDamages trees, gardens or crops
Oleander AphidAphis neriiDamages trees, gardens or crops
Witch-hazel Cone Gall AphidHormaphis hamamelidis
Beech Blight AphidGrylloprociphilus imbricatorDamages trees, gardens or crops
Rice Root AphidTetraneura nigriabdominalis
Rose AphidMacrosiphum rosaeDamages trees, gardens or cropsSources
- Wikipedia: https://en.wikipedia.org/wiki/Stegophylla_essigi
Look it up elsewhere: GBIF · iNaturalist · BugGuide · Wikipedia
Text written 2026-10-27 from the sources above and checked sentence by sentence against them. Data fetched 2026-10-27.