Robberfly - Genus Proctacanthus

Robber flies, also known as assassin flies, are large true flies counted among the most devastatingly effective predators of flying insects. These powerful fliers ambush prey in midair, carrying them to plants to eat them. They often perch, hawk-like from a high vantage point, rapidly descending to catch a meal.

Wasps, bees, grasshoppers and other flies are common meals for a robber fly. It’s not uncommon to see a robber fly eating prey larger than itself. 

Not unlike spiders, they inject venom and enzymes that begin to digest their prey. Robberflies are often seen as beneficial to gardens and farms, as they control the populations of other invertebrates that can become a nuisance. 

Damselbug - Family Nabidae

Damselbugs are predatory insects consisting of over 500 known species. These helpful critters prey on crop pests, and are commonly found in legume fields, along with in many terrestrial environments. Though they are winged, they are relatively poor fliers, flying short to medium distances to evade predators and to get to new hunting territory.

They grab prey with their forelegs, incapacitating it at the same time they stab them with their proboscis. They hunt and consume any invertebrate pray smaller than themselves, but are known to kill and consume grubs, inchworms, and caterpillars larger than their own size.

Carrion Fly or Blow fly - Calliphora vomitoria

One of the best studied insects in all of history, the blow fly has a special place in relation to humanity. Blow flies are the most pernicious, prevalent, and most of all effective decomposer of mammal meat known to science. A female blow fly can lay 150-200 eggs, majority of maggots on any given piece of carrion will be species of blow fly. Adding to their charming nature, they also consume dung as larvae and adults.

Pictured here is a bluebottle fly sampling blood from a possum carcass. These industrious insects are scientifically important as studying temperature records and the Calliphora vomitoria larvae on a human corpse can help forensic scientists determine time of death. Adult bluebottle flies primarily feed on nectar, and are critical pollinators of plants that mimic the smell of rot, like skunk cabbage.

Dance Fly - Family Empididae

Empididae is a large family of flies consisting of no fewer than 3,000 species worldwide. The species found in San Francisco resemble mosquitoes in their size and shape, but do not bother humans. The long, piercing proboscis of a dance fly is specialized to hunt smaller invertebrates, everything from smaller flies, to aphids, to moths and beetles.

Male dance fly species are known to kill their prey and then wrap them in silk, carrying them until they find a female they can present it to as a “nuptial gift”. Female dance flies have developed elaborate mating displays and behaviors to attract this nutritious and protein-rich snack from males, an inversion of what is typical seen in nature (the males posturing and competing for mates). 

Bordered Plant Bug - Largus succinctus

These striking true bugs are among the larger order Hemiptera that can be found in the San Francisco Bay. They use their long proboscis to tap into the xylem and phloem of plants, especially near the flowers, to suck out nutritious juices. They also may eat fruits and nuts.

Though they may present themselves in a garden, they are hapless pests and easily gathered and gotten rid of without use of pesticides, and they rarely cause serious damage to garden greenery. .

Family Tachinidae, genus gymnosoma

Tachinid flies are a colorful and brilliant display of diversity in the order of true flies (diptera). Found worldwide, there are at least 8,200 species of these big-bottomed pollinators, many yet undescribed by scientists, waiting to be discovered. These flies have a brilliant and feral way of reproduction: they lay their eggs on larvae (and sometimes adults) of other species of invertebrates, and the maggots eat their hosts from the inside out. 

Some tachinid flies use sharp ovipositors to inject eggs inside their hosts; others lay eggs that hatch almost immediately, burrowing into the unlucky host. Tachinid larvae are significant killers of caterpillars, worms, and true bugs that are crop pests, and help prevent millions of dollars of crop damage annually.

Species of tachinid flies have even been introduced to North America to control pests that are also alien to the continent. As adults, however, tachinid flies eat only pollen, nectar, and decaying material—if anything at all. Pictured is a tachinid fly of the gymnosoma genus; meaning “naked body,” this genus is less hairy than the classical tachinid fly. 

March flies - Family Bibionidae

March flies, as you might expect, are most common in March, and have short adult lives. Not unlike similar-named mayflies, they die shortly after mating. Their larvae feed on decaying matter in the leaf litter and the soil, and are most active in cooler months.

They sprung up 65 million years ago, in the Tertiary period, and were the most common of any insect for a time. Though they are harmless to humans and the plants we love here in North America, Western Australia has a variety that bites, and enjoys human blood. 

Boxelder Bug - Boisea trivittata

These colorful true bugs have a close relationship with boxelder, maple, and ash trees, where they lay their eggs, grow, and feed. They exhibit a strong preference for the seeds, though they will sometimes feed on the leaves. Though numerous, they do little damage to these trees, nor are they a threat to people, pets, or plants.

They are, however, notorious in some regions, because they congregate in large numbers and often overwinter inside paneling or siding in structures, including homes. The warmth of our buildings attracts them, though they naturally overwinter in leaf litter and in the park of old or fallen trees—another good reason to leave leaves and logs where they lay. 

Snakefly - Order Raphidioptera

These living fossils have remained largely unchanged for close to 140 million years, according to the fossil record. Like butterflies, snakeflies go through “complete metamorphosis, from egg to larvae to pupae to the adult stage. Unlike many insects, they live for several years as larvae.

These odd critters are carnivorous as both larvae and adults, but they feed on pollen from time to time, puzzling scientists who are as yet unsure if pollen is an essential part of the snakefly’s diet. Happily, snakeflies are eager predators of aphids and mites.

They have been suggested as a potential tool for biological pest control, but their long journeys to adulthood (and sexual maturity) means that populations that have been introduced to control agricultural pests have not become well established—yet!

Lacewing - Family Hemerobiidae

These frail beauties, of the order Neuroptera, are named for their often transparent wings. Unlike most insects, they have a sense of hearing—developed most likely because they vibrate their bodies sub-audibly to find a mate. This allows them to avoid predation from bats—dropping to the forest floor when they hear a bat’s echolocation.

Yet, as larvae, their senses are very dull. They are nearly blind, and they sense their prey using the hairs on their bodies. Though they are mostly herbivorous as adults, they are vicious predators as larvae, staking out flowers for aphids and pollinators, grabbing them with sharp mandibles.

Green lacewings are often used as biological pest control, and you can purchase their eggs to distribute in your garden as a way to control aphids!

Fruit fly - Family Tephritidae

Tephritidae is a family of flies, one of the two that are called fruit flies. Often referred to as “peacock flies,” these small and quiet insects feature marked and colored wings, as well as eyes with vibrant shades. Some species of fruit flies are dangerous to crops, including one that feeds only on olive trees and can destroy an entire crop of the fruit.

But most species are harmless, and major pollinators—some are even introduced to crops and pastureland in order to control noxious weeds. Tephritidae flies are among the few species that can create galls, in which they lay their eggs. These invertebrates can hijack the hormonal system of plants, causing them to grow a home with food around the egg.