Yellowish Cuckoo Bumblebee (formerly Fernald’s Cuckoo Bumblebee)

The yellowish cuckoo bumblebee (Bombus flavidus), was until quite recently called by an entirely different name in North America. Bombus fernaldae, commonly called Fernald’s cuckoo bumblebee, was formerly thought to be its own distinct species. However, as of the spring of 2021, Fernald’s is no more. When it was determined that Bombus fernaldae and Bombus flavidus were one and the same, it was decided that henceforth, the species will be called flavidus. In taxonomy this is called synonymization. Synonymization is a common process in taxonomy. The continuous interplay between the ephemeral nature of matter and environmental factors in the lives of these bumblebees is an example of how evolution and discovery in science combine for change in the natural world. Keep reading to learn more about the most widely distributed bumblebee on the planet!

Five Facts about Yellowish Cuckoo Bumblebees

• Until 2021, yellowish cuckoo bumblebees were called Fernald’s cuckoo bumblebees. The bee was named for Charles Henry Fernald (1838-1921), the first recorded professor of economic entomology. Economic entomology is the study of insects and to what degree they help or harm other animals or crops.
• Bombus flavidus is the most broadly distributed bumblebee on the planet.
• Bombus flavidus is found in North America, including Canada and the United States.
• They invade the nests of the confusing bumblebee (Bombus perplexus) the golden Northern bumblebee (Bombus fervidus), the two-spotted bumblebee (Bombus bimaculatus), red-belted bumblebee (Bombus rufocinctus), and the American bumblebee (Bombus pensylvanicus).
• Once a female Bombus flavidus has laid her eggs in a host bumblebee nest, she will leave the nest and not return.

Scientific Name

Flavidus is a Latin adjective meaning yellow or yellowish. In the case of Bombus flavidus, the species name refers to its yellow coloration. Scientific names are used to uniquely identify species, and avoid confusion. Most binomial scientific names are the genus name, followed by the species name. Both words should be italicized, but only the genus should be uppercase. The binomial name often reflects some characteristic of the species such as coloration, habitat, or behavior, as in Bombus flavidus, which is a reference to the cuckoo’s yellow body. Scientific names also commemorate or honor individuals or places, as Bombus fernaldae honored Charles Henry Fernald. By convention, scientific names are usually Latin or Greek.

Appearance

The yellowish cuckoo bumblebee is small and distinguishable by its yellowish coloring. The female yellowish cuckoo has a black head, and a yellow thorax and abdomen. Females may be splotched with areas of black here and there. They are covered in long uneven hairs that are typically pale. The males are smaller than the females but are similarly colored, except for a distinctive deeper yellow ring mid-way down their abdomens. The species lacks pollen baskets, which are necessary to nurture their offspring. They also have vestigial wax glands, which are underdeveloped and are not capable of producing enough wax to construct a nest. These two evolutionary adaptations, which are characteristic of cuckoo bumblebees, have rendered Bombus flavidus incapable of caring for their larvae.

Behavior

Yellowish cuckoo bumblebees are brood parasites and as such depend on other species of bumblebees to rear their offspring. Bombus flavidus queens do not usually assassinate the hose queen. Instead, they infiltrate host colonies, possibly using olfactory mimicry. Olfactory mimicry is the ability to mimic the scent of another species to gain access to their nests or deceive potential mates. Once the cuckoo queen has been accepted by the colony, the cuckoo will lay her eggs in the cells that have been prepared for the host queen’s eggs. Having laid her eggs, the cuckoo leaves the nest and does not return. When her eggs hatch, they feed on the resources of the host colony.

The effect the cuckoo’s offspring has on the host colony and its queen depends on a variety of factors including the size of the host colony, the size of the parasitic brood, and the availability of food. The number of eggs a cuckoo bumblebee deposits in a host nest can be substantial. Depending on the size, strength, and stability of the host colony, the cuckoo larvae can overwhelm the worker caste, and/or affect the viability of the host’s larvae.

The host’s larvae are forced to compete with the cuckoo larvae for food, potentially reducing the survival rate of the host’s offspring. The host colony may be able to successfully rear both their own offspring and those of the cuckoo bumblebee. However, the presence of the cuckoo larvae may have a significant negative impact, and in the most extreme cases can cause colony collapse. Bombus flavidus only have queens and males. There is no worker caste.

Habitat

The yellowish cuckoo bumblebee lives and forages around the nests of its host species. Because the species is so widespread, yellowish cuckoo bumblebees invade the nests of several different species. Chief among them in North America are the confusing bumblebee (Bombus perplexus), the golden Northern bumblebee (Bombus fervidus), the two-spotted bumblebee (Bombus bimaculatus), the red-belted bumblebee (Bombus rufocinctus), and the American bumblebee (Bombus pensylvanicus). These species construct subterranean nests. They live in the Eastern United States, the Northern Tier States, the Maritime Provinces of Canada, and Alaska. Bombus flavidus forage in taiga, tundra, temperate forests, meadows, and grasslands, and urban gardens. The European yellowish cuckoo bumblebee lives in similar habitats in Austria, Finland, France, Germany, Italy, Poland, Slovenia, Spain, and Switzerland.

Diet

Yellowish cuckoo bumblebees are herbivores. They feed on nectar and pollen. Nectar provides them with energy, while pollen provides essential proteins and nutrients that they need to grow and develop. They are generalist foragers. They will take advantage of available flora, though clover, goldenrod, and honeysuckle are among their dietary preferences.

Predators and Threats

Bombus flavidus is vulnerable to a variety of predators, including birds, small mammals, and insects. Some of the predators that feed on cuckoo bumblebees include wasps, hornets, and yellow jackets, as well as certain species of birds, like flycatchers. Yellowish cuckoo bumblebees are also vulnerable to habitat loss, which reduces the availability of food and nesting sites, making it harder for them to survive and reproduce. Yellowish cuckoo bumblebees are susceptible to the effects of pesticides/herbicides, climate change, and other environmental stressors, as well.

Agricultural chemicals pose a significant threat to Bombus flavidus. Herbicides reduce the availability of flowers and other plant sources that bumblebees rely on for food, while pesticides can kill them outright. These agricultural chemicals are also responsible for reducing the overall quality and diversity of habitats. Studies have shown that even low levels of exposure to these toxins negatively affects cuckoo bumblebees, including reductions in colony growth and reproductive success.

Conservation Status and Population

Bombus flavidus is a species of least concern according to the IUCN RED List of Threatened Species. However, bumblebee populations globally have been declining over the last two decades. Therefore it would follow that Bombas flavidus numbers are trending down. Population estimates are unavailable for this widely dispersed species. Cuckoo bumblebee populations tend to fluctuate wildly from year-to-year, so population estimates from any given year are rather nebulous to begin with.

Lifecycle

The lifecycle of Bombus flavidus is divided into four distinct stages: egg, larva, pupa, and adult. The female cuckoo bumblebee queen emerges from hibernation several weeks after her host species. This lag allows the host time to construct a nest. The cuckoo queen immediately sets herself to the task of finding an appropriate nest in which to deposit her eggs. Once she has chosen her target nest, she enters stealthily and patiently awaits her acceptance into the colony. After she has successfully integrated, she deposits her eggs in the cells that have been prepared for the host queen’s eggs. The parasitic cuckoo eggs hatch a day or two before the host’s eggs, giving the cuckoo larva an advantage.
The cuckoo larva rely on the host workers for their sustenance. As the cuckoo larva grow they molt several times before pupating. They will completely metamorphose into adult bees, emerging from their subterranean nests approximately 6 to 8 weeks after their eggs were initially deposited. When the days begin to grow shorter in the fall, yellowish cuckoo bumblebees will find individual shelters in which to overwinter. Come the light spring, the cycle begins again.

Up Next:

• Forest Cuckoo Bumblebee
• Field Cuckoo Bumblebee
• Vestal Cuckoo Bumblebee

1. gbif.org, Available here: https://www.gbif.org/species/1340487
2. val.vtecostudies.org, Available here: https://val.vtecostudies.org/projects/vtbees/bombus-fernaldae/
3. eol.org, Available here: https://eol.org/pages/1065364
4. nps.gov, Available here: https://www.nps.gov/articles/000/upload/Bees-of-Alaska.pdf
5. natureserve.org, Available here: https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.973016/Bombus_flavidus
6. wiatri.net, Available here: https://wiatri.net/inventory/bbb/resources/SpeciesDetail.cfm?ESTID=11436