Essex Skipper

• It is told from its relatives by the tip of the antennae, black underneath, a detail that requires looking at the insect almost head-on.
• It was accidentally introduced into North America around 1910, in Ontario, with a consignment of grass seed, and is now abundant across much of the continent.
• Its eggs overwinter inside the sheaths of dry grasses, which lets it travel in bales of fodder.
• It reached North America by accident around 1910, near London, Ontario, in timothy seed contaminated with its eggs, and today it is established across much of Canada and the north-eastern United States.
• It keeps spreading because the eggs travel in hay bales and modern seed-cleaning techniques fail to remove them.
• There it is a pest of timothy and cocksfoot grown for forage; the treatment threshold is set at six to eight caterpillars per 30 cm square.
• It is told apart from the very similar Thymelicus sylvestris by the antennal tip, black underneath in this species and orange in the other.
• In the United Kingdom it was not identified until 1889, and its range there is also expanding.

Skeleton type

Invertebrate - chitin exoskeleton (insect)

Habitat and environment

Meadows, verges and tall grassland of Europe and North America

Size at birth

The caterpillar measures 1.6 mm on leaving the egg, large in proportion to the size of the butterfly

Sexual maturity

A univoltine and strictly day-flying species; the adults fly from July to August in Europe

Gestation / incubation

The caterpillar forms inside the egg in late July but stays shut in all winter and emerges in early May; it goes through five instars and pupates in June

Litter / clutch size

Rows of about 30 eggs laid inside the leaf sheaths of coarse grasses, in July and August

Sources consulted: Butterflies and Moths of North America · Pengelly (1961), The Canadian Entomologist · Prairie Pest Monitoring Network · UK Butterflies · UK Butterflies, ficha Essex Skipper · Butterfly Conservation Europe · Ficha de especie de Thymelicus lineola · UK Butterflies, ficha Essex Skipper (Frohawk)

Best time: June and July, in tall grassland