The Wool Carder Bee, A Very Bossy Bee

By Zoe Statman-Weil, Pollinator Partnership

Anthidium maculosum is part of the family Megachilidae, commonly called leaf-cutter, carder, or mason bees. While most bees carry pollen on their hind legs, this family is unique because the bees carry pollen on their abdomen. A. maculosum is most commonly referred to as a wool carder bee. It can be found in the middle to west coast of North America and Mexico. It is most studied for its unique, and aggressive, mating patterns.

Anthidium maculosum feeding on a flower.
Anthidium maculosum feeding on a flower. Copyright © 2011 Jillian H. Cowles (photo from bugguide.net).

Male A. maculosum are very territorial. They have been noted to stay by a flower, for examples members of the genus Monarda, for up to 21 days holding off other males while the look for mates. They also display a unique type of mating system that is common in many insects and in some vertebrates as well: dimorphic (different) male size and behaviors. In these dimorphic mating systems, smaller males, or non-territorial drones, tend to keep low and out of the way, while larger, territorial, males aggressively hold on to the best mating spots.

Hard working territorial males find a patch of flowers that looks appeal to them because they know that soon enough females will come searching for food. Throughout the day, and for the duration of their life they will chase away other territorial and non-territorial males from their chosen flower patch to minimize competition for females. A. maculosum territorial males are so territorial that they bump in to other species that enter their mating space, even humans!

The aggressive males will mate with any female trying to feed within their territory. Although the females attempt to avoid the males, they often succumb in order to gain access to flower blossoms. This allowance by the females is referred to as “convenience polyandry”, essentially exchanging mating to gain access to good forage. Due to this male-female relationship, females can mate up to 12 times a week. From the male’s end, mating attempts can happen as often as every 6 minutes since the last male to mate with a bee will most likely fertilize her eggs. The mating process itself is quick, and takes only around 27 seconds.

A. maculosum is more than just a feisty bee. It is also a beautiful bee! While most bees are quite hairy, meal A. maculosum are shiny and slick. Their abdomen is covered with yellow spots that appear in parallel from the top to the bottom. If you ever get a chance to see one, take a closer look at its beauty!

More Information

  • Alcock, John, George C. Eickwort, and Kathleen R. Eickwort. The reproductive behavior of Anthidium maculosum (Hymenoptera: Megachilidae) and the evolutionary significance of multiple copulations by females. Behavioral Ecology and Sociobiology 2.4 (1977): 385-396.
  • Ridley, M. The control and frequency of mating in insects. Functional Ecology (1990): 75-84.

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