A novel method to measure hairiness in bees and other insect pollinators

1. Hairiness is a salient trait of insect pollinators that has been linked
to thermoregulation, pollen uptake and transportation, and pollination
success. Despite its potential importance in pollination ecology,
hairiness is rarely included in pollinator trait analyses. This is likely
due to the lack of standardized and efficient methods to measure
hairiness. 2. We describe a novel methodology that uses a stereomicroscope
equipped with a live measurement module software to quantitatively measure
two components of hairiness: hair density and hair length. We took
measures of the two hairiness components in 109 insect pollinator species
(including 52 bee species). We analysed the relationship between hair
density and length and between these two components and body size. We
combined hair density and length measures to calculate a hairiness index
and tested whether hairiness differed between major pollinator groups and
bee genera. 3. Body size was strongly and positively correlated to hair
length and weakly and negatively correlated to hair density. The
correlation between the two hairiness components was weak and negative.
According to our hairiness index butterflies and moths were the hairiest
pollinator group, followed by bees, hoverflies, beetles, and other flies.
Among bees, bumblebees (Bombus) and mason bees (Osmia) were the hairiest
taxa, followed by digger bees (Anthophorinae), sand bees (Andrena) and
sweat bees (Halictini). 4. Our methodology provides an effective and
standardized measure of the two components of hairiness (hair density and
length) thus allowing for a meaningful interpretation of hairiness. We
provide a detailed protocol of our methodology, which we hope will
contribute to improve our understanding of pollination effectiveness,
thermal biology and responses to climate change in insects.