Tuesday, June 16, 2015

Bees

Metallic Sweat Bees feeding on a Greenheaded Coneflower

     In honor of National Pollinator Week, it makes sense to honor the best of all the animal pollinators: bees. Most people are aware of how important bees are for pollination of plants, including some 70% of our crops. What they do not often realize however is that we have some 400 or so native bee species in our region, most of which are not at all like the introduced European Honeybee. Honeybees were were brought to the USA in to Jamestown, Virginia, in 1627. They are of course extremely valuable for the way we conduct our agriculture and to give us honey, but we need to realize that wild plants were doing fine (maybe even better) before these generalist bees arrived. Our native plants likely would do fine whether honeybees were here or not today. While most people think that all bees are like the social European honeybees (living in hives with a queen, making honey, and only capable of stinging once), they really are the exception and different from the other 4,000 or so other species we have in North America. There are also about 40 species of non native bees in the US, including the European Honeybee.
     The vast majority of our native bees, for example, are actually solitary, with a single female bee taking care of her young, collecting nectar and pollen for them all by herself. She is extremely non-aggressive and many are incapable of even having their stingers pierce our skin. Should that unlikely event happen however, multiple defensive stings are possible. The reason solitary bees do not sting is that they would prefer to fly away and not defend their nest, for if the solitary mother dies, her nest and eggs are dead anyways. Better to fly away and start over. Honeybees on the other hand live for the hive, the workers themselves really not even reproducing, so all they care about is defending their nest, even if they lose their lives stinging in the process.
     Male solitary bees also fend for themselves and are efficient pollinators by the way, unlike male (drone) honeybees. They have no one to feed them other than themselves and so visit flowers and pollinate plants much like the females. No male bees of any species (or wasps for that matter) can sting either, since stingers are modified ovipositors (egg layers) and males cannot lay eggs of course. Only female bees sting.

Ground nesting bees and their holes

     70% of all bees live underground, while the other 30% often rely on cavities in trees, plants, walls, and many other locations. They usually use burrows they dig and then provision with nectar and pollen for their developing young. While each solitary bee lives by herself and takes on all the work alone, if the habitat is right, many female bees may nest near each other. Good real estate in a nice neighborhood can be hard to find (especially since agricultural practices like plowing can be so detrimental to them). After collecting enough food and laying eggs, the mother bee dies and the bee larvae develop on their own until they emerge, often the next year. 
     Another thing many people do not realize is that although bees can visit many different types of flowers to feed on for themselves, almost half of our native species are specialists in the type of pollen they need to feed their young. These specialist bees, often needing the pollen of a single family, genus, or even a single species of flower, are called oligolectic bees. If the specific (normally native) flowers are not available, the bees cannot reproduce. This is another reason to include a great diversity of native flowers in our yards and preserve them in our parks. Bees need the flowers they evolved with or they simply cannot survive.

Hibiscus Bee Ptilothrix bombiformis, digging her burrow

     The one shown above is usually called the Hibiscus Bee, Ptilothrix bombiformis, which needs pollen from plants in the Mallow family (including hibiscus) to reproduce. I noticed these digging their burrows in one of our Natural Resource Conservation Areas, Arlington Forest Park. They do indeed look like a bumble bee (thus the scientific epithet bombiformis meaning "in the form of a bumblebee"), but unlike them, they dig solitary burrows in the ground. Thanks to friend and colleague Sam Droege, one of the best bee guys in the country, for the help in identification.
     These bees are remarkable in that they not only dig burrows, but carry water over on their fuzzy bodies to wet the ground enough to help them in their excavation. The dirt they pull out is often formed into little turrets that surround the entrance to their hole. They are living in this park because they have the bare, well-drained ground they need, a water source nearby, and of course the plants in the Mallow family that they require.
     This is just one of our 400+ bee species. So this National Pollinator Week, honor all pollinators, but realize that none are better than our native bees.

A male Perplexing Bumblebee (Bombus perplexus) pollinating a flower. Bumblebees are one of the few native social bees, though their nests only last one season.

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