Geometer moths

Overview

Geometridae is a very large family of moths, most often called geometer moths (a name that refers to the “earth-measuring” movement of their larvae), or less commonly, geometrid moths. According to the Global Lepidoptera Names Index (LepIndex), there are 23,872 currently recognized Geometridae species in 92 genera in 9 subfamilies worldwide. According to the Annotated Taxonomic Checklist of the Lepidoptera of North America, North of Mexico (Pohl, 2023) there are 1,440 to 1,450 species in 289 genera in 5 subfamilies in North America north of Mexico. Based on an analysis of primary state-level records and citizen science data (iNaturalist.org, BugGuide.net, and Minnesota Biodiversity Atlas), there are 299 Geometridae species in 123 genera in 5 subfamilies in Minnesota.

Geometer moths occur almost everywhere and on every continent, including Antarctica. Many are significant pests of orchard and shade trees. Most adults are active at night and will come to lights.

The larvae move by extending the front of the body forward then bringing the rear of the body up to meet the front, thus creating a “loop”. This is the source of several of the the common names given to the family.

Description

Geometer moths are small to medium-sized and usually have a slender body.

The antennae may be dilated at the tip or not. If they are, then the eyes are bare, not covered with hairs.

On the forewing, the cubitus (Cu) vein appears to have 3 branches. The subcosta (Sc) vein, the first vein behind the leading margin, and the radius (R) vein are parallel and either close together or fused together along the side of the discal cell.

On the hindwing, the Sc vein is abruptly angled downward at the base.

The larvae have only 2 or 3 pairs of false legs (prolegs). These are at the rear end of the body and is the reason for the distinctive mode of travel.