''Pteromalus cassotis'' is a species of parasitic

wasp A wasp is any insect of the narrow-waisted suborder Apocrita of the order Hymenoptera which is neither a bee nor an ant; this excludes the broad-waisted sawflies (Symphyta), which look somewhat like wasps, but are in a separate suborder ...

in the family

Pteromalidae The Pteromalidae are a large family of wasps, the majority being parasitoids of other insects. They are found throughout the world in virtually all habitats, and many are important as biological control agents. The oldest known fossil is known fr ...

that parasitizes the chrysalides of

monarch butterflies The monarch butterfly or simply monarch (''Danaus plexippus'') is a milkweed butterfly (subfamily Danainae) in the family Nymphalidae. Other common names, depending on region, include milkweed, common tiger, wanderer, and black-veined brown. ...

. They are gregarious parasitoids, meaning a single female lays many eggs in a single host. Research into this species has documented that up to 425 adult wasps can emerge from a single chrysalis. The wasps have a heavy female bias, averaging 90% female. Maximum entropy models suggest that the natural habitat of this species encompasses the continental

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

, southern

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

and parts of

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

; areas inhabited by the

caterpillars Caterpillars ( ) are the larval stage of members of the order Lepidoptera (the insect order comprising butterflies and moths). As with most common names, the application of the word is arbitrary, since the larvae of sawflies (suborder Sym ...

, which are the larvae's hosts.McCoshum, S. M., Andreoli, S. L., Stenoien, C. M., Oberhauser, K. S., & Baum, K. A. (2016). "Species distribution models for natural enemies of monarch butterfly (''Danaus plexippus'') larvae and pupae: distribution patterns and implications for conservation". ''Journal of Insect Conservation''. 20(2), 223-237.

References

Pteromalidae Insects described in 1889 Hymenoptera of North America Taxa named by Francis Walker (entomologist) {{Chalcidoidea-stub