Posts Tagged ‘flavidus’

Cuckoo bumble bees

Saturday, July 25th, 2020

What is a Cuckoo bumble bee?

To paraphrase Bumble Bees and Cuckoo Bumble Bees of California by Thorp, Horning, Jr and Dunning: Cuckoo bumble bees are social parasites without worker castes which usurp bumble bee nests and propagate themselves at the expense of their bumble bee hosts.

In other words, a queen cuckoo waits until another bumble bee species has an active nest with lots of workers. She invades the nest and kills the original queen. She then has the workers of the dead queen raise her eggs and larvae, rather than eggs and larvae of their own species. This has similarities to a cuckoo bird, which lays eggs in other birds’ nests.

Cuckoo bumble bees are the tanks of the bumble world: heavily armored and ready for conquest. Cuckoo queens lack a corbiculum (pollen basket) as they never gather pollen to take back to “their” nest.

Queens of non-cuckoo bumble bees collect pollen to feed their first set of workers each spring–so they need a corbiculum to collect and bring home pollen with which to raise the first set of workers. After the first set of workers hatch, the queen stays in the nest laying eggs while the workers go out foraging.

Cuckoos wait until other queens have established a nest with multiple generations of workers before they invade the colony, kill the existing queen and convince the workers to raise cuckoo bumble bee offspring.

Having said that, cuckoo bumbles are cool and part of the ecosystem.
They are a treat to encounter in the field.
Species are not bad or good.
Biodiversity is good.

Recognizing a cuckoo when we see it

If you see an unfamiliar bumble bee (cuckoos are rare relative to most other species in a given area) that seems very deliberate in its movements and walks from flower to flower, look closely at it’s rearmost legs. Is there a corbiculum present? Pollen basket?

If there isn’t then look closer. If no corbiculum, is it heavily armored? Behaviorally I (DJ) have noticed that, as a class, cuckoos often resist flying. They can fly, and do, but when they are on wildflowers they often walk from flower to flower rather than buzz from one to another as non-cuckoos do.

This may be due to the heavier weight of their thick exoskeleton. Because they are raised as warriors to go in and take over existing colonies, including killing the queen and any workers that rise to her defense, they are built much sturdier than non-cuckoos. It may take a lot more energy to fly around therefore more energy efficient to walk.

Cuckoo bumble species in Washington state include:

No pictures of Suckley bumble, B suckleyi available.

Fernald cuckoo bumble, Bombus flavidus/fernaldae

Friday, July 17th, 2020

Field ID tips

The Fernald cuckoo bumble has a continuous yellow band on T4 (no black interruption).

  • T1 = black
  • T2 = black
  • T3 = black
  • T4 = yellow ( insularis, would show a black area in the center)
  • T5 = black (drones may show some orange or pale hairs)

Similar Species

We have three species of cuckoo bumbles in Washington state.

The Fernald cuckoo bumble bee can be distinguished from the Indiscriminate cuckoo bumble bee because the Indiscriminate bumble has a yellow face and a black notch on T4 while the Fernald cuckoo has a black face and a solid yellow T4

The Fernald cuckoo bumble bee, in the west, is a dark bumble. T3 is black. If T1 is yellow or cloudy, then this is not a reliable field mark.

In the Suckley cuckoo bumble bee, T3 is yellow with a black notch. In the case of B. suckleyi, T1 is always black on a queen. So, if T1 and T3 are black, it is most likely a Fernald cuckoo. If T1 is black and T3 shows some yellow, it may well be a Suckley cuckoo bumble bee. If T1 is cloudy, not black or yellow, it suggests Fernald not Suckley.

The key distinguishing feature for separating B. flavidus from B. suckleyi, the Suckley bumble bee, according to the key in Bumble Bees of the Western United States, by Koch, et al, 2012, is the color of the hairs on the back of the head (Occiput). If the hairs on the back of the head are predominantly black it is B. suckleyi. Bombus fernaldae has mainly yellows hairs on the back of the head. This is important to remember, as far as capturing the key elements needed for photographic identification. Make that shot!