Thaumetopoeidae is a small family of moth

Moth

A moth is an insect closely related to the butterfly, both being of the order Lepidoptera. Moths form the majority of this order; there are thought to be 150,000 to 250,000 different species of moth , with thousands of species yet to be described...

s in the order Lepidoptera

Lepidoptera

Lepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...

. The genera in this family have been historically treated as a subfamily within Notodontidae

Notodontidae

Notodontidae is a family of moths with approximately 3,500 known species. Moths of this family are found in all parts of the world, but they are most concentrated in tropical areas, especially in the New World...

 instead.

The larval stage of some Thaumetopoeidae are known as processionary caterpillars, so named because they move in columns in search of food, resembling a procession

Procession

A procession is an organized body of people advancing in a formal or ceremonial manner.-Procession elements:...

. Some of the species, like the Oak Processionary

Oak Processionary

The Oak Processionary is a moth whose caterpillars are pests in oak forests and pose a health hazard because of their poisonous setae , which may cause skin irritation and asthma.- Distribution :...

, can constitute a health hazard.