Plant Flowering Seasons Vs. Bee Seasons

Everyone knows that certain flowers bloom at certain times of the year. For example, most Ceanothus species flower in the spring and native sunflowers and Cosmos bloom during the summer months. These are very predictable seasonal phenomena.

The same type of seasonal activity is also true for bees – some can be expected in spring, others in summer, and still others in early fall. The seasonal patterns of bees and flowers are often tightly connected – bees make sure to wake up from winter hibernation right on time to collect nectar and pollen from their favorite plants. Likewise, plants schedule their blooms to coincide with the emergence of the best pollinators to ensure their pollination and reproduction. This seasonal scheduling is especially clear for many native bees and flowers, who have developed special relationships over long periods of evolution.

For example, during spring, two groups of bees are commonly found visiting several spring ornamentals such as California poppies. These are megachilid bees of the genus Osmia (often metallic green or blue depending on the species) and andrenid bees of the genus Andrena (all black or a combo of buff and black). These two genera usually cannot be found after the first of July. Bumble bees of the genus Bombus are also present primarily during spring visiting a wide variety of ornamental plants.

During the summer, several other megachilid species (non-Osmia) can be observed visiting urban gardens. A few of these species are the size of honey bees and visit several types of ornamental plants. All of these summer “megs” have black and white banded abdomens in contrast to the shiny green and blue Osmia of spring.

Males and females of the anthophorid genus Melissodes are common during the summer and early fall. Female Melissodes are roundish, stocky, hairy and are regular visitors to plants such as Cosmos, Gaillardia, and sunflowers where they get both pollen and nectar (see photos). In contrast to females, males have longer, wirey bodies, and have very long antennae (see photos). Males also visit Cosmos and sunflowers, but for nectar only.

Agapostemon texana of the family Halictidae is another summer-early fall bee. It is occasional to rare in the San Francisco Bay Area, but the striking color differences between males and females makes them worthwhile to search for in your garden. Females have a bright metallic green thorax and abdomen (photos), whereas males have a metallic green thorax and a striped yellow and black abdomen. A. texana can be observed on Cosmos, Grindelia (Gum Weed), and Bidens ferulifolia.

In contrast to the highly seasonal native California bee species, the exotic honey bees can be found commonly year round on numerous flowering plants. Like the native California bees, honey bees also have their preferred flowers.

Recognizing seasonal differences in flowering and periods of bee activity can be useful for planning a garden that can cater to spring, summer, and fall bees.