Early Thorn

Selenia dentaria · Order: Lepidoptera · Family: Geometridae

Damages trees, gardens or crops. The caterpillars feed on leaves of deciduous trees such as birch and alder, so they can damage trees and garden plants.

Source: Wikipedia

Early Thorn
Photo: Donald Hobern, CC BY

Adults have a wingspan of about 28 to 40 mm and show a lot of colour variation, with scalloped wings, three crosslines and a dark spot near the tip of the forewing. They live across northern Europe and much of the Palearctic region, flying in two generations from April through August.

Source: Wikipedia

How to recognize it

The forewings have three transverse lines, a dark apical stain, and the wing edges are scalloped. Colour is highly variable, but the hindwing shows a shallow notch between the radial veins and the costal spots are enlarged where the lines start.

Source: Wikipedia

Size

Wingspan ranges from 28 mm to 40 mm.

Source: Wikipedia

What it eats

Larvae feed on a variety of deciduous trees, especially birch and alder.

Source: Wikipedia

Life cycle

The species produces two generations of adults each year.

Source: Wikipedia

When you see it

Adults are on the wing from April to August.

Source: Wikipedia

Where it comes from

Its native distribution matches the habitat range listed above.

Source: Wikipedia

Lookalikes

The summer form ab. illunaria is smaller and less speckled, while ab. minima is a dwarf form often sharply marked and common in Arctic Norway.

Source: Wikipedia

Questions people ask

What do the caterpillars eat?

They feed on leaves of deciduous trees such as birch and alder.

Source: Wikipedia

When are the adult moths active?

Adults fly in two generations between April and August.

Source: Wikipedia

How can I tell this moth apart from similar species?

Look for three crosslines, a dark spot at the forewing tip, scalloped wing edges, and enlarged costal spots where the lines begin; the hindwing has a shallow notch between the radials.

Source: Wikipedia

Same family (Geometridae)

Willow BeautyWillow BeautyPeribatodes rhomboidariaPale BeautyPale BeautyCampaea perlataDamages trees, gardens or cropsLarge Lace-border MothLarge Lace-border MothScopula limboundataDamages trees, gardens or cropsRiband WaveRiband WaveIdaea aversataYellow Shell MothYellow Shell MothCamptogramma bilineataLarge Maple Spanworm MothLarge Maple Spanworm MothProchoerodes lineolaDamages trees, gardens or crops

Sources

  • Wikipedia: https://en.wikipedia.org/wiki/Selenia_dentaria

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.

How this page works

This is one bug's fact sheet. The colored box at the top says whether it is dangerous. Sections below cover how to recognize it, whether it is a pest, and how to deal with it. The US map shows which states have records; tap a state to see other bugs there.

Every fact on Bug FAQ comes from a named source (university extension sites, government agencies, GBIF, iNaturalist, Wikipedia). The source is linked next to each section. If we have no source for something, we leave it out.