Beneficial Insects

Bees are pollination workhorses, increasing garden production. Many plants will not produce fruit unless flowers are pollinated. Colorful annuals, such as Cosmos, edible African Blue Basil, and Salvias attract bees. You can also allow herbs and other plants to flower to create bee-friendly landscapes.

The University of California at Davis has a garden dedicated to bees. The Honey Bee Haven website has more resources, including a list of plants they grow.

Bees are very active in warm weather. There is simply so much pollen and nectar to collect! Sometimes, a bee colony may swarm. If you see a swarm, don’t panic. As in any other time when working around bees, remain calm, move gently, and give them their space. Bees generally swarm when they are looking for a new home. Swarming bees are loaded with food and are not interested in stinging people. Contact the Bee Guild to have swarms removed.

Female carpenter bees are large, black and shiny. Male carpenter bees are similar in appearance to bumble bees. Both are about an inch long. Males do not sting and females sting only rarely. Carpenter bees are considered beneficial insects because they pollinate many plants and trees. For their nests, they tunnel into unpainted softwoods such as pine, fir and redwood in house or garden structures. Adults over winter in the nests, emerge in the spring, mate, deposit food in the tunnels and lay eggs. The tunnels are sealed with wood pulp and the new adults chew their way out. After the bees emerge, fill the holes with steel wool and wood filler. Apply paint to the surface to prevent re-entry. Further information is available in the UC Pest Note on Carpenter Bees.

Pollination is the process of transferring pollen from the anthers of a flower to the stigma. It is a requirement for the production of fruits and seeds. In addition to wind and water, pollinators include bees, hummingbirds, butterflies, moths, bats, flies, and beetles.

You can support the pollination process—and help counter habitat destruction—by selecting plants attractive to common pollinators. UC has many resources for planning a pollinator garden. Here are a few to get you started!

• How to Attract and Maintain Pollinators in Your Garden, UC ANR Publication 8498
• Creating a Pollinator Garden, UC Master Gardener Program Statewide Blog
• Encouraging Native Bees & Other Pollinators, California Garden Web

Earwigs are third only to snails and slugs in causing plant damage. While they are beneficial because they eat insects such as aphids, they also feed on soft plants. Earwigs can do quite a lot of damage if there is a high population. They feed at night and hide in moist, tight-fitting places during the day. Trap them by putting out moistened, tightly rolled newspaper or corrugated cardboard in the evening. In the morning dispose of the paper and the trapped insects. Other control methods are described in the UC Pest Note on Earwigs.

Certain flowers help attract natural enemies of pest insects in the garden. Tiny wasps that parasitize certain insect pests or their eggs need pollen and nectar to survive. Predatory insects (syrphid fly larvae, lady beetles, lace wings, and many others) and mites survive on pollen and nectar from flowers when pest populations are low, and some feed on pollen in order to reproduce.

Most of these beneficial insects are small, and so the best flowering plants to include in the garden are those that have small flowers that have pollen and nectar easily accessible and that bloom throughout the season. Avoid flowers that are difficult to weed out when they reseed.

Many flowers that attract beneficial insects are easy to start from seed and this month is a good time to start them – some indoors any time or outdoors later in the month after frost danger has passed. Examples include sunflowers (try dwarf varieties like ‘Sunspot’ for smaller spaces), calendula, cosmos and many herbs like dill, basil and borage.  

Other flowers and herbs that attract beneficial insects are easier to buy as plants. A few examples that can be planted this month are coreopsis, asters, and thyme.

Reference info:
UC Pest Note on Biological Control and Natural Enemies of Invertebrates
UCCE notes on Attracting Beneficial Insects to Your Garden.

UC ANR has a publication titled "How to Attract and Maintain Pollinators in Your Garden" that discusses the benefits of providing flowers for pollinators and has a list of pollinator plants that are successful in most California gardens.

More information: Beneficial Insects

Lady beetles develop through four life stages: egg, larva, pupa, and adult by Jack Kelly Clark, UCANR

For more information: Aphid Eaters

Do your rose bush leaves have smooth round holes in them? The likely culprit is the female leafcutter bee. The bee cuts smooth round or oval leaf fragments and uses them to line each underground brood cell that she fills with nectar and pollen. When the cell is ready, a single egg is sealed inside. The larva pupates (matures) in the chamber and emerges in the spring.

Rose leaves seem to be their favorite. The hole in the leaf is much larger than an ordinary caterpillar would make and is very smooth as if a miniature cookie cutter was used. The bee can chew off a leaf fragment in less then a minute with its sharp jaws.

Like all bees, leafcutter bees are important pollinators and should not be killed.

Butterfly populations fluctuate in response to climate and habitat conditions. Many have specific host plants on which they feed and breed. Some common plants for attracting butterflies are milkweed, lantana, buddleia, and zinnias. For an extensive list of relationships between specific butterflies and host plants, see Art Shapiro's Butterfly Site at UC Davis.

Spider web, Johns Hopkins University

More information: Arachnophobia Video