Bug FAQHolly Blue
Celastrina argiolus · Order: Lepidoptera · Family: Lycaenidae
Also called: Holly Blue Butterfly, Spring Azure
The holly blue is a small butterfly with violet-blue wings and silver-blue undersides, found across Eurasia. Its larvae feed on holly and many other plants, and it has several generations from spring to autumn. Population numbers fluctuate because a parasitic ichneumon wasp attacks its caterpillars and pupae.
Source: Wikipedia
How to recognize it
The butterfly shows violet-blue wings with pale silver-blue undersides marked with black dots; males have a shining violet-blue top side with a thin white edge on the front wing margin.
Source: Wikipedia
Size
Its wingspan measures about 2.6 to 3.4 cm.
Source: Wikipedia
How to get rid of it
Population cycles are linked to a parasitoid ichneumon wasp that lays eggs inside holly blue caterpillars; the emerging wasp kills the chrysalis.
Source: Wikipedia
Where it lives
It often perches with its wings nearly closed or held at roughly a right angle.
Source: Wikipedia
Life cycle
Adults appear in spring, again in July, and sometimes a third time in late August-September; pupae are attached to the underside of leaves and are ochre with brown spots.
Source: Wikipedia
When you see it
Adults are seen in spring, July, and occasionally late summer; activity also peaks in June and autumn.
Source: Wikipedia
Where it comes from
The species occurs throughout Eurasia.
Source: Wikipedia
Lookalikes
It is the national butterfly of Finland.
Source: Wikipedia
Where it is found in the US
Recorded in 30 of 51 states and DC. Most records: New York, Arizona, California, Utah, Washington, New Mexico, Idaho, Colorado.
Darker = more records. Counts are museum and citizen-science records, not population size.
Source: GBIF
Months it is reported in the US
Source: GBIF
More photos
Questions people ask
Are holly blues a problem for gardens or crops?
They feed on many garden plants, but the sources do not describe them as damaging pests.
Source: Wikipedia
Why do holly blue numbers go up and down?
Their numbers fluctuate because a parasitic ichneumon wasp attacks their caterpillars and pupae.
Source: Wikipedia
Same family (Lycaenidae)
Sources
- Wikipedia: https://en.wikipedia.org/wiki/Holly_blue
Look it up elsewhere: GBIF · iNaturalist · BugGuide · ITIS · Wikipedia
Text written 2026-10-22 from the sources above and checked sentence by sentence against them. Data fetched 2026-10-22.