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Insects and other arthropods

Giant ichneumon

Megarhyssa atrata

Tabs group


These insects look like large, slender wasps. They have a yellow head with a dark stripe between the eyes. The thorax and abdomen are dark, either black or dark brown. Their long legs are mainly yellow, while their four elongated, narrow wings are almost black.

Females have an impressive 12- to 15-cm long dark brown ovipositor.

This species resembles two other ichneumons found in the same habitat in Quebec: Megarhyssa macrurus and M. greenei. Giant ichneumons are recognizable by their blackish-brown abdomens. In addition, they have the longest ovipositors.

Life cycle

Giant ichneumons are ectoparasitoids, meaning that they need a host to complete their life cycle, that they are external parasites (not living inside the host) and that they kill their host as they grow.

In Quebec, adults take wing from May to September. They live about 27 days. After mating, females look for a host to lay their eggs on – most often pigeon horntail (Tremex columba) larvae. These larvae tunnel into wood, and female ichneumons use their long ovipositors to reach them and lay their eggs. The young ichneumons feed on their hosts during their four larval stages. They then pupate before emerging into the open air as adults. The entire life cycle lasts about two years.

Geographic distribution

The species is found in southeastern Canada and the northeastern and central United States.

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