Genus: Anthidium Fabricus, 1804
Subgenera: Anthidium, Gulanthidium, Nivanthidium, Proanthidium, Severanthidium, Turkanthidium
Common name: wool carder bees
Anthidium are commonly referred to as “wool carder bees” because females scrape trichomes off leaves and stems with their mandibles to use as nesting material (Gonzalez and Griswold 2013; Wilson and Carril 2016). Anthidium generally have robust bodies with broad, flattened, and parallel-sided abdomens. Their integument is black with conspicuous yellow maculations (Michener 2007). They range in body length from 6–19 mm (Michener 2007). Unlike many other bees, males are generally larger than females (Michener 2007).
Anthidium contains more than 160 species in six subgenera worldwide (Gonzalez and Griswold 2013). There are 36 species that occur within the U.S and Canada (Wilson and Carril 2016) and 28 species that occur in Mexico. All North American species are in the subgenus Anthidium except for the invasive species A. oblongatum, which is in the subgenus Proanthidium. The greatest diversity of Anthidium is thought to occur in the Great Basin (24 species) and on the Colorado Plateau (23 species) (Gonzalez and Griswold 2013).
(modified from Michener 2007, unless otherwise stated)
Anthidium can be difficult to differentiate from other Anthidiini genera, especially those that Michener (2007) places in Series B. Anthidium can be distinguished by the combination of characters above.
Anthidium oblongatum is native to Europe and the Middle East and was accidentally introduced to eastern Pennsylvania in 1995 (Miller et al. 2002). They have become established in eastern Pennsylvania, Maryland, New York, and New Jersey. They have since expanded to northern Illinois and southern Canada (Miller et al. 2002; Gonzalez and Griswold 2013).
Anthidium manicatum, the European wool carder bee, is native to Europe. Males are well known for their highly aggressive territorial behavior (Miller et al. 2002). In the early 1960s, they were accidentally introduced to eastern North America, specifically New York (Miller et al. 2002; Gonzalez and Griswold 2013). They have since spread rapidly across the U.S. and are commonly found in most states in the late summer. Anthidium manicatum has also been introduced in Canada, Brazil, Argentina, Uruguay, New Zealand, and the Canary Islands (Miller et al. 2002).
Plant host preferences vary widely among species of Anthidium. A few species are generalists and visit a variety of plants. Others prefer specific plant families, such as Hydrophyllaceae, Fabaceae, and Asteraceae. Researchers have found that a few species may specialize on plants such as Astragalus and Phacelia (Gonzalez and Griswold 2013). In addition, Anthidium collect trichomes from pubescent plants, such as Asteraceae and Lamiaceae, and use them for nesting material (Gonzalez and Griswold 2013).
All species of Anthidium are solitary. Most Anthidium make nests in pre-existing cavities in soils, walls, wood, and stems, but they have also been observed inhabiting abandoned beetle, wasp, and bee burrows (Michener 2007). Nests are lined with trichomes shaved from pubescent plants, such as those from the genera Artemisia, Cirsium, and Pseudognaphalium (Gonzalez and Griswold 2013). Trichomes are also used to create the walls between nest cells. Once the nest is constructed, food is provided, and eggs are laid in the cells. Male eggs are laid at the back of the nest, unlike most other male bees that develop at the front of the nest. Due to the larger size of Anthidium males, they are likely laid at the back of the nest to allow them more time to develop (Wilson and Carril 2016). Materials, such as trichomes, pebbles, wood, plant matter, and lizard feces are then used to pack the upper portion of the cavity, above the cells, to create nest plugs (Krombein 1967). The chosen materials are species-dependent.
Anthidium palliventre and A. rodecki only inhabit sand dunes and will dig their own nests. Females have a collection of long hairs on their foretibia, which allows them to dig in the sand. Similar to other species of Anthidium, nests are lined with trichomes.
Males often exhibit territorial behaviors over host plant patches, which secures their food source and impacts their mating success (Alcock et al. 1977; Villalobos and Shelly 1991). Larger male Anthidium have been observed to be more successful at defending and holding territories and mating (Michener 2007; Gonzalez and Griswold 2013).
Anthidium are found on all continents except for Australia (Michener 2007). They are uncommon in areas such as sub-Saharan Africa, Madagascar, and the tropics in southern Asia and Indonesia. Anthidium occurs within most of the Western Hemisphere (Gonzalez and Griswold 2013). They have specific habitat preferences, with most of the species within the U.S. preferring dry, desert habitats along the west coast (Wilson and Carril 2016). Two species (A. palliventre and A. rodecki) are found only on sand dunes in the western U.S. (Gonzalez and Griswold 2013; Wilson and Carril 2016). Only four species are known to reside in northeastern North America (A. psoraleae, A. maculifrons, A. oblongatum, and A. manicatum), with the latter two being recently introduced (Miller et al. 2002; Wilson and Carril 2016).