Forest Cuckoo Bumblebee

The forest cuckoo bumblebee (Bombus sylvestris), also called the four-coloured cuckoo bumblebee, is a species of bumblebee commonly found in Northern and Central Europe, and Russia. They have distinctive yellow and black striped, hair-covered bodies. Forest cuckoo bumblebees are brood parasites that live underground in nests that they invade and usurp from unsuspecting hosts. Keep reading to discover more about these resourceful insects.

Five Facts about Forest Cuckoo Bumblebees

• Female and male forest cuckoo bumblebees have different dietary preferences
• They are effective pollinators
• Forest cuckoo bumblebees are brood parasites, laying their eggs in the nests of other bumblebee species.
• They live underground in the nests of Bombus pratorum, Bombus jonellus, and Bombus monticola.
• Forest cuckoo bumblebees are called cuckoo, because, like cuckoo birds, they lay their eggs in the nest of a different species.

Scientific Name

The scientific name Bombus sylvestris is Latin for buzzing sylvan. Sylvan means located in woods or forests. The species was named by Amédée Louis Michel le Peletier (1770-1845), a French botanist, with a special interest in Hymenoptera. le Peletier christened the forest cuckoo bumblebee with its binomial name because forest cuckoo bumblebees are found in forests. Bumblebees are all in the genus Bombus (buzzing) thanks to the deeper and more resonant tone of their wing vibrations. This is due to structural differences in the cuckoo’s thorax. Cuckoo bumblebees have a longer, stronger thorax that allows for a more powerful wing beat and deeper wing buzz. This evolutionary adaptation also protects the queen when she is attacking the host queen.

Appearance

Forest cuckoo bumblebees are a small species in which females are larger than males. These little cuckoos typically measure between 0.55 – 0.59 inches long, with wingspans of 1.18 – 1.37 inches. They are black with a yellow thoracic collar and a yellow abdominal band. There is a melanic, all-black, form of this species that is primarily visible in the northern reaches of its range. Their tails are white, though males have an orange tip, while the tip of the female’s tail is black. Females tend to keep their tails tucked. They are hairy by cuckoo standards and are effective pollinators. However, they lack pollen baskets and do not collect pollen for their offspring. Unlike some other species of cuckoo bumblebees, Bombus sylvestris have functional wax glands.

Behavior

Forest cuckoo bumblebees are brood parasites. As a result of evolutionary adaptations these bees are no longer able to adequately nourish and care for their offspring. Therefore, it is essential for them to locate a host nest in which to rear their young. Bombus pratorum, the early bumblebee or early-nesting bumblebee is the species most likely to be preyed upon by forest cuckoo bumblebees. However, forest cuckoos are also known to usurp the nests of Bombus jonellus, the small heath bumblebee, and Bombus monticola, the bilberry bumblebee or mountain bumblebee.

The forest cuckoo queen emerges in late spring to early summer, several weeks after her host species has emerged. This is another revolutionary adaptation that allows the host to prepare the nest prior to the forest cuckoo overtaking it. It is thought that the queen uses her sense of smell to find a suitable nesting site for her brood. Once she has chosen a nesting site she will attack the host queen, killing it and subjugating the worker cast to rear her young.

They are studies that point to forest cuckoo bumblebees’ ability to co-habitat with their host species, in which each produces and raises offspring. The study determined that the forest cuckoo bumblebee larvae were able to coexist with the host bumblebee larvae, both of which fed on the nest’s resources without consequence. The study concluded that the presence of the cuckoo bumblebee larvae did not adversely affect the development or survival of the hose larvae. However, in most cases, the colony is focused on raising the cuckoo’s brood.

Habitat

Forest cuckoo bumblebees are visible where flowering plants are in abundance. Gardens, parks, woodlands, and deciduous forests are suitable habitats for forest cuckoo bumblebees. The presence of flowering plants is important for the survival of the colony. The host workers collect nectar and pollen to feed the larvae and the queen. Forest cuckoo bumblebees live underground but come out daily to forage.

Diet

Bombus sylvestris are generalist foragers who feed on nectar and pollen. Thistles and brambles are favorites. Forest cuckoo queens also feed on deadnettle, dandelion, horse chestnut, and lavender. Forest cuckoo males prefer clover. As pollinators, they play an important role in the reproduction of these plants by transferring pollen from one flower to another. The workers collect nectar, which provides energy for the colony, and pollen, which is fed to the developing larvae. Additionally, the queen consumes nectar and pollen to build up her energy stores before starting a new colony.

Predators and Threats

Some of the most common predators of forest cuckoo bumblebees include birds, like bee-eaters and sunbirds. Insects such as assassin bugs and praying mantises eat cuckoos. Crab spiders eat bumblebees that get snagged in their webs. Bumblebee larvae can fall prey to a variety of predators, including spiders, parasitic wasps, and ants.

The most immediate threat facing forest cuckoo bumblebees is habitat loss. The destruction of natural habitats due to human activities such as agriculture, urbanization, and deforestation reduces the populations of these bumblebees. Other major threats to the continued existence of forest cuckoo bumblebees are climate change, pesticide, and herbicide use, and competition for resources.
Changes in temperature, precipitation patterns, and extreme weather events can disrupt the timing of flowers and the life cycles of bumblebees, making it difficult for them to find food and reproduce.
Pesticides and herbicides used in agriculture harm bumblebees by reducing their immunity and fertility.
Finally, non-native species and other pollinators reduce the availability of food sources for forest cuckoo bumblebees, while increasing the competition for existing resources.

Conservation Status and Population

Bombus sylvestris is a species of least concern on the IUCN Red List. This means that it is not considered to be in immediate danger of extinction. However, its population has declined in recent years.
Population estimates for forest cuckoo bumblebees are undetermined, but its overall population is believed to be trending down, as is the case with the majority of bumblebee species.

Lifecycle

The lifecycle of Bombus sylvestris begins in late spring when the forest cuckoo queen bumblebee emerges from hibernation and begins to search for a suitable nesting site. Incapable of building a nest of her own, the cuckoo queen must usurp the nest of an established colony. That’s where the unsuspecting host species enters the fray. When the cuckoo queen has made her choice, she swoops in, killing the existing queen and subjugating the workers. Once accomplished, the queen cuckoo deposits her eggs in the nest that was prepared for the host queen’s eggs.

After a few days, the eggs hatch into larvae, which the subjugated worker bees nourish with nectar and pollen from nearby flowers. The queen forest cuckoo bumblebee stays with her brood in the nest of the host species to ensure that her offspring are well cared for. The cuckoo queen stays in the nest for several weeks until her offspring have matured and are ready to emerge as adult bees. The exact amount of time required for development varies depending on an array of environmental conditions, but in general, bumblebee larvae take 6-8 weeks to pupate and mature into adults. After pupation, the adult bees emerge, ready to fly and forage for food. In the fall, the cuckoo bumblebees take shelter individually in which to overwinter, waiting for spring when the cycle resumes.

Up Next:

• Barbut’s Cuckoo Bumblebee
• Vestal Cuckoo Bumblebee
• Red-Tailed Cuckoo Bumblebee