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University of Minnesota Extension

Species guide - species detail

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Passaloecus monilicornis (aphid wasp/square headed wasp)



Passaloecus are aphid wasps in the family Crabronidae. They are known for their large mandibles in which they carry prey back to their nests. These mandibles are also used in clearing debris out of nesting sites. In Minnesota, the genera represented inhabit the Holarctic and Nearctic regions. P. monilicornis are considered to be in the insignis group of species.


Passaloecus monilicornis are small-sized species of Passaloecus, usually about 4mm or less in length. They have black bodies with black or dark brown hind trochanters and femora. Two characteristics that set P. monilicornis apart from others are a large truncate clypeal lobe that almost looks bidentate in nature. Also, the complete absence of a scrobal sulcus. Both female and male P. monilicornis wasps have bidentate mandibles, but the mandibles of the females are broader, larger, and less sharp.

Nest Structure

Passaloecus monilicornis build their nests in the stems of plants – most commonly in the stems of American Elderberry and Miscanthus grasses. They are also known to inhabit abandoned beetle galleries or, in the case of the Minnesota Bee Atlas, holes in wood blocks. P. monilicornis partition these cells with resin and provision them with aphids.

Hole Sizes

No information at this time.


This species appears to be univoltine or bivoltine in the Midwest, completing one or two generations per year in Minnesota.

Activity Period

Passaloecus monilicornis are active in Minnesota from April to September.


Vincent, D. L. 1973. A revision of the genus Passaloecus (Hymenoptera: Sphecidae) in America north of Mexico. The Wasmann Journal of Biology, 36(1 & 2): 127-198.

Minnesota Record Map

These data are from the Minnesota Bee Atlas project.

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