This summer I stumbled upon a sweat bee nest while moving some old boards. The nest was between two boards and this is what it looked like when I lifted the top one off. (Sweat bees, family Halictidae, are often metallic, shiny green or blue.)
Sweat bees vary from solitary to social. This nest had multiple adults, which probably indicates they were living socially. Does anyone recognize the species?
All life stages were present. In this cell there is a ball of food and what looks like an egg (it seems to have a knob at one end?). Usually the food is a mixture of pollen and nectar, hence the yellow-orange color. See the water beads in the cell? The sweat bees line the cells with wax.
The older larvae are plump grubs. Prior to pupating, the larvae enter a resting stage called a prepupa.
Sweat bee pupae look like most bee pupae. You can see their eyes, mouthparts and antennae. This species does not appear to spin a cocoon.
Everything is pretty neat and tidy.
I tried to replace the board, but when I checked the next day, it was obvious the disturbance was too much. Many of the cells were empty.
The nest was overrun with snails (I think they ate the larval food),
and of course, ants.
What a difference a day makes in the life of a sweat bee.
Tarantula hawks are large, colorful wasps in the genus Pepsis. They are found throughout the southwestern United States.
The wasps have a close relationship with the desert or rush milkweed plant (Asclepias subulata). Their long legs slide into the grooves of the milkweed flowers, picking up the bright yellow pollinia. As they move from flower to flower, the wasp pollinates the plant.
We often watch these huge tarantula hawks flying in towards the desert milkweed plants in our yard. You can see them from quite far, flying five to six feet above the ground. To be anthropomorphic, the wasps seem like they've been flying for miles and when they locate the milkweed, they target and land. You can almost hear them sigh, "Finally!"
Except they have long legs for carrying and dragging tarantulas, so landing is often less than graceful. Here's a typical landing sequence:
Tarantula hawks are quite beautiful once they get right side up.
Most of us realize that honey bees are important insects. They pollinate essential food crops, as well as make honey and beeswax. We know that honey bees need flowers to survive because they feed on nectar and pollen. We probably think of small plants, such as clover or dandelions, when we think of honey bee food. What is the role of trees in honey bee survival? It turns out, a role as big as the trees themselves.
Here in the Southwest, mesquite trees are an important source of pollen and nectar for honey bees. In the northeastern United States, trees such as oak, willow, black locust and tulip poplar produce large amounts of nectar and/or pollen. Commercial beekeepers use their bees to pollinate almonds, apples, and citrus. Trees are significant food sources for honey bees.
Honey bees use trees as a source of other products, as well. When beekeepers open the honey bee hive, they have to use a special tool like a small crowbar, called a "hive tool." That is because the honey bees produce a sticky, gummy material called "propolis" that they use to coat the inside of the hive. Propolis is made from plant resins the bees collect and carry in the pollen baskets on their back legs, mixed with materials from their own bodies, such as waxes.
Because I had just written a post about tree resins and ants, I decided to look into what is known about tree resins and honey bees. Although the existence of propolis has been known for a very long time, and many uses for it suggested, not a lot of scientific investigation has been done. It does appear, however, that honey bees are using the tree resins for some of the same reasons that ants do, namely to fend off disease organisms.
Scientist Marla Spivak, who works at the University of Minnesota's College of Food, Agricultural and Natural Resource Sciences department, has been working with a team to find out more about the anti-disease properties of propolis.
She has found that the honey bees in her area collect the raw material for propolis in the form of resin from birch and poplar trees, as well as some conifers. When they looked at the chemistry of propolis, they found some 300 to 500 compounds. The team is now separating the components and looking for individual compounds with biological activity against either honey bee or human disease-causing agents.
Turns out that trees are important to honey bees in more ways that we realized.
Edit: (Once again, we have a blog post inspired by a book. This week it is a children's book, The Hive Detectives: Chronicle of a Honey Bee Catastrophe by Loree Griffin Burns and photographs by Ellen Harasimowicz. If you are interested in finding out more about the book, check Wrapped In Foil for a review and Growing with Science for related hands on activities for children.)