Habitat: Nest of Polistes lanio. Brazil.

Among the Hymenoptera, few genera have created greater dispute than the
anomalous genus Trigonalys of Westwood. Mr. Macgillivray one day brought
to the British Museum the nest of a Brazilian Polistes. My friend, Mr.
Frederick Smith, is well known for his profound knowledge of the
Hymenoptera, Exotic and British, which, though he has studied them ONLY
fourteen years, are better known to him, perhaps, than to any other
living Entomologist; the instant that he looked at the nest, he
exclaimed, "Why, here is Trigonalys!" and certainly a large, black-headed
creature, not very like Polistes, protruded from one of the cells. Mr.
Smith, on the 7th April, 1851, communicated this piece of information to
the Entomological Society of London, and in their Transactions his brief
memoir was lately printed. I cannot do better than give it in Mr. Smith's
own words. Mr. Smith, subsequently to the reading of the paper,
ascertained that the species had been described in the great work of De
Geer, a book of which it would be well to have a condensed new edition.
Mr. Smith says:

"John Macgillivray, Esquire, Naturalist to Her Majesty's Ship
Rattlesnake, lately presented to the British Museum the nest of a South
American species of Polistes, which he says is very abundant at St.
Salvador, where even in the streets it attaches its nest under the eaves
of houses; the species is the Polistes lanio of Fabricius, and in all
probability the Vespa canadensis of Linnaeus; a specimen of the species
is preserved in the Banksian Cabinet. On examining the nest, I found it
consisted as usual of a single comb of cells, having in the centre at the
back a short footstalk, by which the nests are attached in their
position; the comb contained sixty-five cells, the outer ones being in an
unfinished state, whilst twenty-two of the central ones had remains of
exuviae in them, and one or two closed cells contained perfect insects
ready to emerge; about half a dozen of the wasps had the anterior portion
of their bodies buried in the cells, in the manner in which these insects
are said to repose. In one cell I observed the head of an insect
evidently of a different species, it being black and shining. On
extricating it, I discovered it to be a species of Trigonalys; I
subsequently carefully expanded the insect, and it proved to be the
Trigonalys bipustulatus, described by myself in the Ann. and Mag. of
Natural History,