We have a wide variety of bees and wasps in San Mateo County. As the weather warms up, these insects become more active and more numerous in yards. Although capable of stinging, most species are non-aggressive, and only sting defensively when their nests are threatened.
Get to know your winged black-and-yellow neighbors!
Click on the name to be taken to the iNaturalist page showing representative species.
Honey bee – Small, fuzzy, with tan-and-black stripes. Often carry pollen on their back legs. Builds wax combs in nests in tree holes or other natural cavities, or kept by beekeepers. Not aggressive. Important pollinators and producers of honey.
Bumblebee – Very robust and fuzzy. Size variable. Often have a yellow face and dark black body – or black with yellow stripes. Builds nests in the ground – usually in existing burrows or holes. Not aggressive. Important pollinators.
Carpenter bee – Largest bee in California (up to an inch long). Females are entirely black with a fuzzy round body. Males of the most common species (Valley carpenter bee) are a golden color. Bores its way into wood (usually dead branches or untreated deck wood). Nests as a small group or a few individuals tending a brood. Not aggressive. Important pollinators.
Paper wasp – Black and yellow with a skinny waist and long spindly legs. Builds nests with open combs near the eaves of buildings. Not aggressive, but will defend their nest. Predators of garden pests.
Mud dauber – Black and yellow or metallic blue-black with an extremely skinny long waist and long, dangly legs. Builds nests out of mud on the side of buildings. Predator of other insects – especially spiders (including black widows). Not aggressive. Muddaubers belong to the family Sphecidae. All are solitary with each female building an individual nest in which to lay her eggs. The nests are made out of mud, two to three inches across, with rows of round cells containing the developing embryos. The female wasp stocks each cell with a spider—food for the young wasps when they hatch. Mud daubers are not very aggressive and rarely sting. You can leave mud daubers and their nests alone, or, if you prefer, simply remove the nest.
Gall wasps - Gall wasps (also called gallflies) are tiny little wasps that protect their eggs and larvae by parasitizing plants (usually oak trees). The wasp injects a material into the plant and then lays an egg. The plant then forms a gall, much like a tumor, around the wasp larvae where it can develop safely and with all the food it could ever need until it is ready to bore its way out and enter the world again. The type of gall that is created is unique to the wasp so that you can identify the species of wasp just by looking at the gall!
Parasitoid wasps - Parasitoid wasps prey on other insects (and sometimes on each other) not by eating them, but by injecting them with eggs. These eggs hatch into larvae and begin to devour their host while it is still alive. They are highly specific about what sort of host they prefer, and you can often guess the wasp species just by seeing their prey. This group is one of the most diverse groups of hymenopterans; they come in a wide variety of colors, shapes and sizes. Parasitoid wasps are considered highly beneficial to humans in that they control agricultural pests like beetles, caterpillars, and flies.
Syrphid flies - Also called hover flies or flower flies, syrphid flies are black and yellow striped just like a wasp but have neither stinger nor venom. These clever flies are even capable of mimicking the way wasps fly and are often confused for their more aggressive brethren. Syrphid flies are important pollinators of flowering plants worldwide and may even specialize on a few plants (such as the slipper orchid in southwest China). They may also prey upon aphids and leafhoppers helping to control these pests.
Bee flies - Like the syrphid fly, bee flies resemble bees and may have evolved that way to avoid predation. They can neither bite, nor sting. These flies are important pollinators and, like the parasitoid wasps above, may help to control pests by laying their eggs near the eggs of other species, usually beetles, wasps, or solitary bees. Once theirs eggs hatch they feed on the eggs and young larvae of the bee fly’s prey. Unlike parasitoid wasps, bee flies are not picky about the host they choose and may unfortunately kill species that are beneficial to humans.
Asian giant hornets (aka 'Murder Hornets') (Vespa mandarinia) - Are NOT in California, and there is no current evidence they are headed this way. In fact, they have a somewhat overlooked history of averted introductions into North America. As recounted in an article in the online journal Science News, V. mandarinia was previously detected in 2016 by a USDA inspector in Sacramento. A shipment containing an entire nest of live larval and pupal hornets was intercepted at the San Francisco airport. The nest had likely arrived from Asia, where these insects are sometimes harvested as ingredients for food or drink.