Bumblebee

Cold-weather pollinators

Bumblebees can fly at much lower temperatures than honeybees:

• Honeybees stop flying below ~13 °C; struggle below 18 °C.
• Bumblebees routinely fly at 5 °C; some Arctic species fly at near-freezing.

The fuzzy body (more accurately a thick coat of branched hairs) traps body heat. Bumblebees also warm themselves through “flight muscle uncoupling” — disengaging the wings from the muscles and shivering rapidly to generate heat before takeoff.

This cold tolerance is why bumblebees are essential for pollinating crops in cool climates and high altitudes — particularly tomatoes (commercial greenhouses use captive bumblebees), blueberries, cranberries, and squash.

Buzz pollination

Bumblebees uniquely perform buzz pollination (sonication) — vibrating their flight muscles at high frequency while clinging to flowers, dislodging pollen from anthers that can’t release it through normal jiggling.

This technique is essential for tomato production — tomato anthers are tube-shaped and only release pollen through buzzing. Greenhouse tomato production worldwide depends on commercial bumblebee colonies.

Honeybees can’t buzz-pollinate; they’re outcompeted by bumblebees for tomato pollination.

Annual colony cycle

Unlike honeybees (whose colonies persist year-round), most bumblebee colonies are annual:

1. Spring — overwintered queens emerge, find nest sites (often abandoned rodent burrows).
2. Summer — queen produces workers; colony grows to 50–500 individuals.
3. Late summer — colony produces new queens and males.
4. Fall — new queens mate, find hibernation sites; the rest of the colony dies.
5. Winter — only mated queens survive, hibernating underground.

A single mated queen restarts the entire cycle alone the following spring.

A species in trouble

Several bumblebee species are declining sharply. The North American rusty patched bumblebee (Bombus affinis) became the first U.S. bee placed on the federal endangered species list in 2017, after a 90% population decline over 20 years. Causes include pesticide exposure (especially neonicotinoids), habitat loss, climate change, and a fungal parasite (Nosema bombi) that may have been introduced via commercial bumblebees.

Garden support — planting native flowers, avoiding pesticides, leaving some lawn unmown — has measurable positive effects on local bumblebee populations.