Anthidium formosum

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Taxonomy

Family: Megachilidae
Subfamily: Megachilinae
Tribe: Anthidiini
Genus: Anthidium Fabricius, 1804
Subgenus: A. (Anthidium) Fabricius, 1804
Species: Anthidium formosum Cresson, 1878
Common name: none

Overview

Anthidium (Anthidium) formosum are dark brown to black with yellow maculations (Gonzalez and Griswold 2013). Females have yellow to ferruginous pubescence, sometimes with white pubescence on the sides of the thorax and abdomen, and have a body length of 11.5–13.5 mm (Gonzalez and Griswold 2013). Males have white pubescence on their head and thorax, and range in length from 12.8–15.4 mm (Gonzalez and Griswold 2013).

Diagnostic characteristics

(modified from Gonzalez and Griswold 2013)

• Labrum lacks basal protruberances and preapical projections.
• Female mandible has six teeth.
• Female propodeal triangle is shiny and finely imbricate to lineolate.
• Female hind tibia without anterior carina.
• Female T1–T5 depressed marginal zones are dull, and coarsely and densely punctate.
• Female T1–T5 discal areas are weakly elevated and weakly shiny.
• Female T1–T5 distal margins are narrow.
• Female T6 distal margin is medially projected with a deep emargination.
• Female T6 is elevated along the midline with a small, distinct lateral spine.
• Female T6 preapical carina and depressed apical rim is absent.
• Male S4 has a reddish-brown brush of long apical hairs on a concave distal margin.
• Male S6 basal margin is bilobed.
• Male S6 lateral lobes are subquadrate and median lobe is absent.
• Male S7 is apically narrow.
• Male S8 apical process is laterally flattened.
• Male T6 lateral spine is straight, and longer than T7 median spine.
• Male T7 lateral lobe is apically subtriangular with a convex outer margin and concave inner margin.

May be confused with

Anthidium formosum may be confused with A. illustre based on the large body size, female T6 distal margin with a deep median emargination, and elongate male penis valves (Gonzalez and Griswold 2013). Both sexes of Anthidium formosum can be differentiated from A. illustre by the lack of preapical projections on the labrum (Gonzalez and Griswold 2013). Male A. formosum can also be differentiated from A. illustre by the shape of S4 and S6 (Gonzalez and Griswold 2013).

Phenology

Anthidium formosum adults have been recorded in flight from May to September, with peak activity occurring from the last half of June to the first half of August (Gonzalez and Griswold 2013).

Host associations

Anthidium formosum is a generalist that has been observed visiting a variety of species within Asteraceae, Boraginaceae, Fabaceae, Lamiaceae, Orobanchaceae, and Ranunculaceae (Gonzalez and Griswold 2013).

Nesting behavior

Anthidium formosum nesting biology was determined from trap nests (Horning 1969; Parker 1987). Nests plugs are constructed out of a variety of materials, ranging from only trichomes to trichomes with pebbles, small pieces of wood, masticated plant material, or lizard dung (Krombein 1967). Horning (1969) also observed resin in the nest plugs of three A. formosum nests in Idaho.

Distribution

Anthidium formosum occur throughout California, Oregon, Washington, Montana, Wyoming, and Colorado. They are found primarily in the Great Basin, Snake-Columbia, and Wyoming Basin shrub steppe; Colorado Plateau shrublands; Wasatch, Uinta, and Great Basin montane forests; and eastern Cascades and Sierra Nevada forests (Gonzalez and Griswold 2013).

​Distribution map generated by Discover Life -- click on map for details, credits, and terms of use.