Bug FAQAlder Leaf Beetle
Agelastica alni · Order: Coleoptera · Family: Chrysomelidae
Source: Wikipedia
Adults are small, about 6 to 7 mm long, and are black or metallic blue; larvae are black. They live on grey or speckled alder, sometimes on black alder, hazel, birch, or hornbeam. One generation appears each year; adults overwinter as winged insects and emerge in spring.
Source: Wikipedia
How to recognize it
Adults are black or metallic blue and about 6 to 7 mm long; larvae are black.
Source: Wikipedia
Size
The beetle measures roughly 6 to 7 mm in length.
Source: Wikipedia
Where it lives
It is found on grey or speckled alder and, if needed, on black alder, hazel, birch, or hornbeam.
Source: Wikipedia
What it eats
Both adults and larvae feed on alder leaves, especially grey or speckled alder, and may use hazel, birch, or hornbeam when alder is scarce.
Source: Wikipedia
Life cycle
Adults overwinter as winged insects, emerge in spring, and produce one generation per year.
Source: Wikipedia
When you see it
Winged adults overwinter and become active in spring.
Source: Wikipedia
More photos
Same family (Chrysomelidae)
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Dogbane Leaf BeetleChrysochus auratus
Colorado Potato BeetleLeptinotarsa decemlineataSources
- Wikipedia: https://en.wikipedia.org/wiki/Agelastica_alni
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.