Anthidium atrifrons

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Taxonomy

Family: Megachilidae
Subfamily: Megachilinae
Tribe: Anthidiini
Genus: Anthidium Fabricius, 1804
Subgenus: A. (Anthidium) Fabricius, 1804
Species: Anthidium atrifrons Cresson, 1868
Common name: none

Overview

Anthidium (Anthidium) atrifrons females vary greatly in their coloration. The face, scutum, and legs can be entirely black, somtimes with ivory to yellow on the mandible, scutum, legs, and rarely the clypeus (Gonzalez and Griswold 2013). In females, the hairs on the sternal scopa and legs range from a black or dark brown coloration to white. Females range in body length from 7.5–10 mm, and males can range in body length from 11.5–13.1 mm (Gonzalez and Griswold 2013).

Diagnostic characteristics

(modified from Gonzalez and Griswold 2013)

• Female clypeus is entirely black and prominently convex when viewed in profile.
• Female hind tibia without anterior carina.
• Female labrum with two large preapical projections and without basal protuberances.
• Female fore basitarsus is covered with dense, long tomentum, and short, semi-erect, unbranched hairs.
• Female T1–T5 discal area punctures are 1–3 puncture widths apart, the integument somewhat shiny in between the punctures.
• Female T1–T5 depressed marginal area densely punctate medially, punctures less than one puncture width apart.
• Female T6 has a distinct median emargination, a narrowly depressed apical rim, and an indistinct lateral angle.
• Male S4 with median apical brush broad, and with dense black hairs. The apical margin of S4 is nearly straight medially.
• Male S6 with lateral projections and sublateral carinae.
• Male S7 with apical margin somewhat truncate.
• Male T7 lateral lobe rounded to subtriangular.

May be confused with

Female A. atrifrons with dark hair and ivory markings can appear similar to A. emarginatum, whereas forms with pale hair and strong yellow markings may be confused with A. tenuiflorae, A. collectum, or A. duomarginatum. Female A. atrifrons can be differentiated from the other species by the denser tomentum on the fore basitarsus, as well as the depressed apical rim of T6 that progressively dissipates until absent about halfway between the lateral angle and the median emargination (Gonzalez and Griswold 2013). Male A. atrifrons may appear similar to A. dammersi because of the similarly shaped T7, but can be differentiated by the shapes of the lateral lobes of S6 and T7 (Griswold and Gonzalez 2013).

Additionally, A. emarginatum and A. atrifrons appear to have different elevation preferences. Anthidium atrifrons are often found in montane habitats, while A. emarginatum can be found in lowland environments (Gonzalez and Griswold 2013).

Phenology

Anthidium atrifrons adults have been recorded in flight from April to October, with peak activity occurring from June to early August (Gonzalez and Griswold 2013).

Host associations

Anthidium atrifrons is a generalist that has been observed visiting a variety of species of Apiaceae, Asteraceae, Boraginaceae, Brassicaceae, Caprifoliaceae, Caryophyllaceae, Crassulaceae, Fabaceae, Lamiaceae, Onagraceae, Plantaginaceae, Polemoniaceae, Polygonaceae, and Rosaceae. Anthidium atrifrons has shown a strong preference for Phacelia (Boraginaceae), with visits occurring at 64%. Anthidium atrifrons also collects trichomes from two Asteraceae species, Pseudognaphalium canescens and P. stramineum, to line their nests and create nest plugs (Davidson 1895).

Nesting behavior

A. atrifrons and A. emarginatum were, at one time, considered the same species. The specimen associated with these nesting observations can no longer be located, preventing the identification of the species. Therefore, it is equally likely that the nesting observations correspond to either species. The recorded observations found the species nests in the ground in abandoned Anthophora (Apidae) nests (Davidson 1895). Cell partitions and nest plugs are comprised of trichomes from two Asteraceae species: Pseudognaphalium canescens and P. stramineum (Davidson 1895).

Distribution

Anthidium atrifrons occur throughout the western U.S., primarily in montane habitats (Gonzalez and Griswold 2013).

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