Select Page

This may be remembered as the year of the bee at Curbstone Valley.  It started when we installed a few hives of honey bees on the farm this spring, but we also greatly understand the importance of the native bees that frequent our crops and flowers.

Research has demonstrated that diversification of pollinators is critical for farms, and that organic farms situated close to wild-land habitats may depend more on native bees for pollination, than conventional farms.  Most conventional farms are almost wholly dependent on European honey bees for pollination as they lack the habitat necessary to sustain native pollinators. [1]

Here we’re striving to do what we can to support both our honey bees, and our native bee populations.

It’s important to recognize that many of the same threats to honey bee populations, including some diseases [2], and risks from exposure to pesticides, may have similar detrimental effects on native bee populations.

The most obvious single threat to native bees, however, is habitat degradation.

Native bee populations co-evolved with regionally adapted native plant species, which tend to become sparse in populated areas, where landscapers,  and gardeners select plants for their aesthetic value, and farmers choose plants solely for their economic value, rather than their importance to the survival of native pollinator species.

Approximately 1600 native bee species have been recorded in California [3]. We’ve noticed a number of native bees here in the last couple of years, including green sweat bees (Agapostemon spp.), carpenter bees (Ceratina and Xylocopa spp.), bumble bees (Bombus spp.), leaf cutter bees (Megachile spp.), and now, these intriguing looking long-horn bees (MelissodesDiadasia, or Svastra, spp. — trust me, unless you’re an entomologist, this group of bees can be tricky to nail down a definitive ID).

Long-horn bees are in the family Apidae, and the tribe Eucerini.  By recognizing some of the different native bees present on the property, and learning about their foraging habits, nesting habits, and significance as pollinators, we can ensure that we take the necessary steps to encourage, and support, their populations on the farm.

Until this summer we hadn’t noticed any long-horn bees in the gardens, perhaps because the gardens didn’t hold much of interest to these particular bees.  Many long-horned bees are specialist foragers, targeting only plants in the Asteraceae family, such as our native Asters, and Encelia, as well as our garden Sunflowers, and Rudbeckias.  In fact long-horn bees are one of the key native bee species for pollinating commercial sunflower crops [4].

Although we’re not exactly sure which species of long-horn bee this is, the Rudbeckias, and sunflowers we’ve planted this year near the greenhouse, seem to be enticing these particular bees.  Our best educated guess is that this bee might be Melissodes robustior, one of the most common long-horn bee species in California.  Regardless, once the sun’s rays hit these blooms in the morning, it’s almost impossible to miss these bees.  I almost feel as if I owe the bees an apology for not planting the Rudbeckias sooner.

Long-horn bees range from from 7.5 to 18 mm in length.  Male long-horn bees have remarkably long antennae, as shown in some of these photographs, for which they acquired their common moniker, and an elongated body shape. Whereas females have shorter antennae, and a more rounded body shape.

In addition to long antennae, the most notable physical characteristic of these bees is that their legs are significantly more hairy than their honey bee cousins.

The females are responsible for gathering pollen on their brush-like leg hairs (scopae), as well as foraging for nectar, and depositing food in their underground nests to sustain developing larvae.

Any native-bee-friendly garden is only enhanced by planting a diversity of nectar and pollen-rich native, and heirloom flowers.  However, suitable nesting sites are also critical for helping to sustain native bee populations. Native bees don’t live in hives like their honey bee counterparts, and many species construct underground nests.  Desirable nesting sites, and nests  however, can easily be damaged, or destroyed, as a result human activity.

To encourage native ground-nesting bees, it’s important that some areas of bare soil are left in the gardens. Although mulches are important for conserving moisture for plants, and improving soil texture, mulching every square inch of garden space eliminates important nesting habitat for ground-nesting native bees.

Here we mulch individual plants, not entire surfaces, mostly our vegetables and fruits, to avoid providing too much cover for ravenous rodents, like our meadow voles.

For any ground nesting bee species it’s also imperative that nesting sites aren’t disturbed, as these bees spend much of their lives developing underground, many only emerging to mate and forage for a few short weeks each year.  One of the worst gardening practices for ground nesting bees, other than the obvious use of pesticides, is rototilling garden soils. This not only destroys soil structure, but can also destroy nests.

Next time you consider reaching for the rototiller, ask yourself, do you have ground nesting bees, like these long-horn bees, in your garden?  Hand digging is not only healthier for the gardener, but it’s also better for the bees!

Although we’ve been judicious about planting flowers in the Asteraceae family, as generally they tend to cause the rapid crystallization of honey, the fact these long-horn bees seem to favor plants in this family, highlights the importance of planting a diverse variety of flowers in the gardens.  With careful planning we hope to keep both the honey bees, and the native bees happy.

Next time you think you see a honey bee in the garden, take a closer look, it may in fact turn out to be a native bee!

To learn more about identifying, and providing suitable habitat for native bees, see:

California Pollinator Project: Citizen Scientist Pollinator Monitoring Guide

Farming For Bees: Guidelines for Providing Native Bee Habitat on Farms

——————

[1] Kremen, C. et a. 2004. The Area Requirements of an Ecosystem Service: Crop Pollination by Native Bee Communities in California. Ecology Letters. Vol: 7 p. 1109-1119.

[2] Singh R, Levitt AL, Rajotte EG, Holmes EC, Ostiguy N, et al. 2010 RNA Viruses in Hymenopteran Pollinators: Evidence of Inter-Taxa Virus Transmission via Pollen and Potential Impact on Non-Apis Hymenopteran Species. PLoS ONE 5(12)

[3] Frankie, G.W., et al. Native Bees Are a Rich Natural Resource in Urban California Gardens. July-September 2009. UCANR Publication.

[4] Xerces Society Fact Sheet: Native Bee Pollination of Hybrid Sunflowers.