Pachysomoides fulvus

(Cresson, 1864)

Pachysomoides fulvus is a small ichneumon that parasitizes paper wasps (Polistes spp.) in North America. The female wasp lays on larvae or pupae inside the exposed paper comb nests of its . It ranges from New York to Florida and west to California and British Columbia, though it does not appear to be abundant anywhere. The is notable for targeting social wasps that are typically well-defended, making it a specialized despite its relatively small size.

Pronunciation

How to pronounce Pachysomoides fulvus: //ˌpækɪˈsoʊmɔɪdiːz ˈfʊlvəs//

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Identification

Pachysomoides fulvus is a small ichneumon . It can be distinguished from its Pachysomoides stupidus, which occurs in the southeastern United States (North Carolina to Florida, Texas, and southern Illinois), by the latter's black and white banded pattern with orange legs. P. fulvus lacks this striking coloration. The is also characterized by its of hovering near paper wasp nests rather than by distinctive morphological features visible to casual observers.

Distribution

New York to Florida, west to California and British Columbia. Distribution records include Medicine Hat, Canada.

Host Associations

Polistes fuscatus - Northern Paper Wasp; laid on larvae or pupae inside nest
Polistes apachus - Apache Wasp; observed being targeted by P. fulvus in greenhouse setting

Life Cycle

The female lays on larvae or pupae of paper wasps inside the of the exposed paper comb. Young nests populated only by the foundress are especially vulnerable since the must leave the nest to hunt food for her offspring. An observation suggests eggs may be laid in cell walls even when only an egg is present at the bottom, with the ichneumon larva emerging after the larva hatches. Development details beyond this are not well documented.

Behavior

Female are known to hover in the vicinity of paper wasp nests, waiting for opportunities to access larvae or pupae. They appear to be stealthy in their approach, targeting nests when wasps are absent or distracted. The is remarkably tolerant of close proximity to active paper wasp colonies, which are typically aggressive toward intruders.

Ecological Role

Pachysomoides fulvus functions as a of social , potentially helping regulate paper wasp . Its presence may exert on nest defense and nest architecture in Polistes .

Similar Taxa

Pachysomoides stupidusCongeneric in the U.S. with similar ; distinguished by black and white banded coloration with orange legs, and more gregarious larval feeding (up to 31 larvae observed on one pupa). Occurs in the southeast from North Carolina to Florida, Texas, and southern Illinois.

More Details

Taxonomic note

Described by Cresson in 1864. The Pachysomoides belongs to Ichneumonidae, a large family of . Most ichneumon wasps parasitize Lepidoptera caterpillars; only a small percentage target other insects such as wasps.

Research limitations

Detailed information is difficult to obtain without access to paywalled journal articles. The appears to be understudied relative to its P. stupidus, which has been the subject of more detailed behavioral research.