Natural Enemies
In addition to cuckoo bees, nesting bees have several natural enemies including those that prey on them while visiting flowers and others that parasitize adults or larvae. Natural enemies threaten the reproductive success and survival of both adults and larvae. Adults navigate these threats searching for a mate, finding food on flowers, defending the nest, or performing tasks to construct or provision their nests.
Natural enemies are an important part of a healthy ecosystem and, in most cases, should not be considered pests. Even though they may impact a percentage of a bee population through predation or parasitism, they in turn often have their own natural enemies. And it is this complexity of interactions that help form stable and diverse ecosystems.
In Flight Predators
A number of insects and birds capture bees while on the wing. Philanthus (beewolves), a genus of predatory wasps, capture bees to feed to their offspring. Robber flies (family Asilidae) often explosively launch from a perch to capture bees (and other insects). Some robber flies even resemble or mimic bees. Particularly in early spring, songbirds such as chickadees and migratory warblers take advantage of the concentrated number of male bees patrolling flowering plants or nesting sites, catching the bees while on flowers or on the wing.
Philanthus (Beewolves)
Philanthus (beewolves) are predators of bees (less often wasps). Philanthus females search for and capture bees on flowers. To avoid detection, these predatory wasps hover downwind, then when they confirm by smell that a bee is present, they fly toward the flower to see and capture the bee. The Philanthus female must work quickly to subdue a captured bee. She stings the bee, often multiple times, with venom that causes partial or full paralysis. Once immobile, the wasp clasps the bee with her legs, clutching it beneath her while she flies back to her ground nest. The alive but immobile bee is cached in the nest brood cell, and a single egg is laid on it or another bee in the same cell.
Family Asilidae (Robber Flies)
Robber flies (family Asilidae) are predatory as larvae and adults. Adults perch on foliage and watch for insects to capture. They are fast flyers, often launching from their perch to chase and capture their prey on the wing. Some are bee mimics (see the bumble bee mimics in the photos above), and this mimicry helps them avoid detection by their prey. After capturing prey with their spiny legs, they use their piercing mouthparts to inject salivary enzymes into the prey, a process that begins dissolving the prey's tissues. Robber flies have large eyes and often have long beard-like hairs on the face.
Predators Ambushing Bees on Flowers
A number of insects and spiders perch on flowers and lie in wait to ambush bees. These insects and spiders often have specialized anatomy such as oversized or long forelegs for grabbing prey, and mouthparts that inject immobilizing venoms. The venoms liquefy the victim making it easier for the predator to consume them. See below for some examples of ambush predators.
Phymata (Ambush Bugs)
Phymata (ambush bugs) belong to the family Reduviidae; this family includes both assassin and ambush bugs. These insects (and all insects in the order Heteroptera) have straw-like mouthparts that are used either for piercing and sucking fluids from plant tissues or from prey. Phymata have oversized forelegs that are employed to catch unsuspecting prey while they visit flowers. The prey is then quickly subdued by the ambush bug as it inserts its mouthparts into the bee and injects venom that begins dissolving they prey's tissues.
Family Thomsidae (Crab Spiders)
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Crab spiders in the family Thomsidae are lie-in-wait predators of bees and other flower-visiting insects. Some species of these predators change color to blend in with the color of the flower. These spiders have long legs that they use to catch bees. Once a bee is captured, the spider injects venom into the bee through its mouthparts, immoblilizing the bee and dissolving its tissues.
Parasitoids of Adult Bees
Family Conopidae (Thick-Headed Flies)
Thick-headed or conopid flies in the family Conopidae are parasites of adult bees. Thick-headed fly adults are common around patches of flowering plants, perching on vegetation or visiting flowers. Some in the subfamily Conopinae have very constricted abdomens and mimic wasps. These flies lay their eggs into their host while on the wing. Conopid fly females have special appendages on the underside of their abdomen for prying open the abdominal segments of their host to insert their ovipositor into the bee's abdomen. The fly larva feeds on the host bee's abdomen, then the thorax, hollowing out the bee over time. Amazingly, the bee remains alive while the fly larva feeds on its tissues. When the fly larva is ready to pupate, some flies have the ability to coerce the bee to excavate a hole in the ground to allow the larva to pupate within the shell of the bee's exoskeleton belowground.
Physoconops parasitize bees in the familly Megachilidae.
Physocephala parasitize bees in the genera Anthidium, Anthophora, Apis, Bombus, Eucera, Halictus, Megachile, and Nomia.
Physocephala tibialis parasitizes Bombus (bumble bees).
Myopa parasitize bees in the genera Apis, Andrena, and Anthophora.
Dalmannia parasitize bees in the genus Andrena and possibly other spring-active bee genera.
Zodion parasitize bees in the genera Bombus, Apis, Andrena, Nomia, and Agapostemon.
Family Sphaerulariidae (Parasitic Nematodes)
While Bombus (bumble bee) gynes hibernate in a shallow burrow in the ground during the winter, they can become infected with a parasitic nematode, Sphaerularia bombi. The nematode enters the diapausing gyne, migrates to the circulatory fluid (hemocoel), and finally to the uterus and reproductive tract. Once there, it begins turning the organs inside out and a large cavity or sac begins to form. The nematode then pauses activity and overwinters in the host. After the infected gyne emerges in spring, the nematode reinitiates activity, absorbing nutrients from the hemocoel. The parasite changes the behavior of an infected bumble bee gyne and renders it sterile. Instead of searching for a nest in spring post-emergence, infected gynes make multiple attempts at excavating a hibernation burrow. While the gyne excavates at various sites, the nematode offspring exit the host out the anus, into the soil where they will infect new gynes hibernating that autumn or winter.
© Don Leaon
A Bombus impatiens (common eastern bumble bee) gyne infected with the parasitic nematode Sphaerularia bombi excavates a hole in the ground in spring. The infection changes the behavior of the host. Instead of searching for a nest in spring, the infected gyne makes attempts to dig a hiberation burrow.
Parasitoids of Bee Larvae
There are a number of parastoids that prey on bee larvae. Some have very creative methods to successfully transport the larvae to the nest including hitchhiking on adult bees, launching eggs into the nest while hovering over it, or sneaking into the nest to lay eggs. Scroll down to view images and descriptions of common bee nest/larval parasites.
Family Chrysididae (Cuckoo Wasps)
Cuckoo wasps in the family Chrysididae are typically bright metallic green or blue-green, resembling metallic green sweat bees in the family Halictidae. To help protect them from attacks by the host bee (or wasp), they have heavily pitted exoskeletons and other armature covering vulnerable locations on their exoskeleton. Adult females enter a bee nest and lay an egg in a fully provisioned brood cell. The cuckoo wasp larva does not begin feeding on the bee larva until it reaches its final (fifth) instar stage and is about to prepare for pupation. Their hosts include bees in the family Megachilidae.
Chrysis prey on bees in
the family Megachilidae.
A Chrysis female monitors nesting cavities.
Hedychrum are parasitoids of beetle wasps in the genus Cerceris.
Family Mutillidae (Velvet Ants)
Velvet ants are ant-like wasps in the family Mutillidae that are common in sandy sites that contain bee nests. They can also be observed visiting flowering plants to feed on nectar. Velvet ant females are ectoparasitoids of bees, often ground-nesting species. Velvet ant males have wings, but the females are wingless, resembling ants. Females monitor the nests of their hosts, often tapping their antennae on the ground to determine the location of a host belowground. Once a host is found, they excavate their way into the nest to seek out a fully provisioned and sealed brood cell. They sting the bee pupa and lay an egg on it, then the velvet ant larva feeds on the host pupa, eventually killing it.
A Dasymutilla bioculata female excavates her way to a bee nest in sandy soil.
A Timulla vagans female investigates a Halictus rubicundus nesting aggregation.
A Pseudomethoca simillima female investigates a sandy area containing Andrena asteris nests.
Family Gasteruptiidae (Carrot Wasps)
Carrot wasps in the genus Gasteruption (family Gasteruptiidae) are unique-looking wasps with a long linear abdomen, enlarged hind tibiae, and neck-like propleura. These wasps are parasitoids of bees and wasps. Their larvae feed on the host egg or larva as well as the pollen or insect provisions. Using their long ovipositor, females either lay an egg into the nesting cavity while perching at the entrance (sometimes through the material capping the nest) or back into an open cavity to lay an egg in a partially or fully provisioned brood cell. The first instar larvae have large mandibles that are used to consume the host egg (or larva). The second instar larva loses these oversized mandibles and consumes the host provisions. The larva may continue development and emerge as an adult or overwinter in a prepupal stage.
A Gasteruption female visits Aralia racemosa.
Family Torymidae
Monodontomerus, a genus of wasps in the family Torymidae, are ectoparasitoids of wasps, bees, beetles, caterpillars, and flies. Females search for nesting cavities of bees and lay their eggs in the cocoon of the prepupa or pupa. After entering the nest and finding a host prepupa or pupa, the female walks on top of the cocoon, tapping her antennae on the silken enclosure. She determines the appropriate place on the cocoon to insert her ovipositor, then lays several eggs on the host. The first instar larva emerges within a few days, begins feeding on the host, and ultimately passes through four instar stages. It then pupates and emerges as an adult.
A Monodontomerus female
investigates an Osmia lignaria nest.
Family Eulophidae
Wasps in the genus Melittobia (family Eulophidae) are tiny ectoparasitoids of cavity-nesting solitary bees and wasps. Melittobia has three forms of offspring: males blind and unable to fly, females with non-functional wings, and females with functioning wings. After finding a host prepupa or pupa, the female stings it, then feeds on the hemolymph (blood-like fluid) for a few days. She then lays a cluster of eggs on the prepupa or pupa. The female-biased offspring from this first cluster of eggs have short, non-functional wings. This first brood of females lay their own cluster of eggs on the prepupa or pupa, then their larvae feed on the host, develop, and ultimately fully consume the host. This brood is also female-biased. However, these females have functional wings. After these females mate with males, they disperse from the nest to search for a new host.
Melittobia females inside a stem cavity nest.
Family Anthomyiidae (Satellite Flies)
Flies in the genus Leucophora (family Anthomyiidae) are cleptoparasitoids of ground-nesting solitary bees. Hosts include bees in the family Andrenidae. Leucophora females follow the host bee on their return foraging trips back to her nest. The bee may try to shake off or evade the fly by flying in a zigzag pattern. The fly, if successful in tracking the bee, either follows the bee into the nest or, perching on the ground or nearby vegetation, waits outside of the bee's nest. When the host bee leaves the nest, the fly enters the nest and lays an egg in a fully provisioned brood cell containing pollen provisions. The fly larva consumes these provisions as it develops.
A Leucophora female perches on vegetation and monitors the activity of ground-nesting bees.
Family Bombyliidae (Bee Flies)
Flies in the family Bombyliidae are endoparasites of ground-nesting insects including solitary bees. The adult flies are common flower visitors, consuming nectar and pollen with their long proboscis. Fuzzy in appearance, these flies are mimics of small bees. Females coat their eggs with sand particles that they collect by dragging their abdomen across bare sandy soil; the particles accumulate in their sand chamber or psammophore, then eggs are laid into this chamber. After identifying the location of a host nest, the bee fly female hovers above the nest, then launches the sand particles and eggs cached in her sand chamber into or near the entrance. The first instar fly larvae crawl around inside a bee's nest, searching for a brood cells containing a bee larva.The fly larva does not begin consuming the bee larva right away. Instead, it waits until the bee larva has finished developing before feeding on it. The fly larva pupates in the brood cell, overwinters in this development stage, then makes its way to the ground surface via a wriggling movement. The adult emerges from this pupal enclosure and flies off.
A Paravilla female collects sand particles in a chamber in her abdomen.
A Bombylius sp. visits Acer rubrum flowers in early spring.
A Bombylius validus female collects sand particles in a chamber in her abdomen.
Family Sapygidae (Sapygid Wasps)
Wasps in the genus Sapyga (family Sapygidae) are cleptoparasites of cavity-nesting bees in the genera Osmia, Heriades, and Chelostoma. Sapyga females enter a nest, then lay an egg in a fully-provisioned brood cell. The first instar wasp larva consumes the host egg, molts, then begins feeding on the pollen provisions in its second instar stage. When all the provisions have been consumed, the wasp larva spins a silken cocoon to pupate within. It overwinters as an adult in the cocoon, then emerges from the cavity nest the following growing season.
A Sapyga martinii male visits Osmorhiza longistylis.
Family Leucospidae
Wasps in the genus Leucospis (family Leucospidae) are cleptoparasites of cavity-nesting bees in the genus Megachile including Megachile campanulae and M. relativa. Leucospis females have a long ovipositor held in a sheath on the top of the abdomen. After locating the nest of their host, they unsheath the ovipositor, raise their abdomen upward, then push the ovipositor through the nest closure materials of the Megachile nest. Eggs are either attached to the brood cell wall or laid on the bee larva. The first instar wasp larva kills the host larva, molts, then begins feeding on the brood cell provisions. It pupates in the brood cell but does not spin a cocoon, then emerges as an adult.
A Leucospis affinis female drills her ovipositor into a Megachile nest (right).
The Hitchhikers - Triangulins
Family Ripiphoridae
(Wedge-shaped Beetles)
Beetles in the genus Ripiphorus (family Ripiphoridae) are both endo- and ectoparasitoids of ground-nesting solitary bees in the families Halictidae and Apidae. Their larvae are hitchhikers that catch a ride to the host's nest. Ripiphorus adults are short-lived, reportedly living for a few days. Females lay their eggs on flowers or flower buds. Their first instar larvae (triangulins) attach themselves to a bee visiting the flower, hitchhiking back to the nest attached to the bee. Once inside nest brood cells, the beetle larvae feed on the bee larvae internally as an endoparasite, then switch to feeding externally as an ectoparasite. After consuming the bee larva and pupating, the beetles emerges from the ground nest as adults.
A Ripiphorus male on a fleabane flowerhead.
Family Meloidae (Blister Beetles)
Blister or oil beetles in the family Meloidae can be both parasitoids and cleptoparasitoids of ground-nesting bees. Some females in this family are unable to fly because they lack developed wings (under their elytra) or have small poorly developed wings. As such, many travel across the ground in search of sites to lay clusters of eggs on the soil, at the entrance of nests, or under an object on the ground. The first instar larva (triangulin) attaches itself to a bee on the ground, on flowers, or by entering the nest burrow of the host. After discovering a fully provisioned brood cell, it consumes the host egg (or larva), molts to the second instar stage, then feeds on the pollen provisions. In some cases, the larva may consume a bee larva in another brood cell after consuming all the pollen provisions. The beetle pupates in the brood cell, overwinters as an adult, then emerges a week or more prior to the host bees emerging.
Blister beetle triangulins attached to an Andrena female.
Tricrania sanguinipennis
Tricrania sanguinipennis is a parasitoid of bees in the genus Colletes. The flightless adult beetles are common where Colletes inaequalis nesting aggregations occur. In early spring, the adult beetles emerge one to three weeks prior to the emergence of the Colletes adults and crawl around on the sandy soil near the nest aggregation. In spring, adult beetles mate, then the females lay clusters of eggs under an object lying on the ground. A first instar larva attaches to an adult bee and transfers to a female bee during mating. It is then transported into the nest by a female bee. The larva gains access to a provisioned brood cell, kills the host bee egg, molts, then feeds on the pollen provisions. The adult beetle overwinters in the ground and emerges a few weeks prior to the bees.
Lytta aenea is a parasitoid of Colletes.
Zonitus vittigera. Beetles in this genus are parasitoids of a number of bee genera.
Meloe impressus. Females lays eggs on the ground, and the first instar larvae (triangulins) climb up vegetation and attach themselves to bees visiting flowers.
Family Chaetodactylidae (Mites)
There are a number of genera of mites in the family Chaetodactylidae that are associated with bees. Some of the bee/mite relationships are beneficial. For example, there are mites that feed on the fungi that grows in brood cells or the waste of bee larvae; some feed on the natural materials lining a nest. Other mites predate on other mites that cause harm to bee larvae. Mites that are natural enemies of bees feed on or destroy the host egg or larva, then feed on the pollen provisions. Many insects that have a beneficial or mutualistic relationship with mites have a special area on their body to carry mites called an acarinarium. For example, some mason wasp genera in the subfamily Eumeninae have an acarinarium underneath the rim of their first tergite. Some female bee genera have an acarinarium and these genera usually have a neutral or beneficial mutualism with the mites. The acarinarium can occur next to the tegulae, on the propodeum, on the first tergite, on the sternum, or in the genitals. Bees that lack an acarinarium often carry mites that are harmful. Mites attach to bees as an adult bee exits its brood cell and passes through adjoining nest cells in a nesting cavity, or if a bee survives development in a brood cell that contains mites. Mites can transfer from male to female bees during mating, hitchhiking on the female to the nest. The harmful mites often attach to areas on the bee's body that is difficult for the bee to groom or reach. To learn more about bee mite identification, visit the Bee Mite ID website.
Mites on an Andrena ziziae male. Mites known to associate with Andrena either cause no harm or their impact is unknown.
A number of mite genera are associated with Bombus (bumble bees) including both harmful and beneficial ones and some with unknown impacts. These mites can occur externally under the tegulae, on the thorax, abdomen, or legs, and internally within the tracheae (breathing tubes).
Harmful mites in the genus Chaetodactylus on an Osmia lignaria male. These mites consume bee eggs/larvae and cell provisions.
Mites (genus Parapygmephorus) on an Agapostemon virescens female. These mites are beneficial, feeding on the feces of bee larvae.
Family Stylopidae (Twisted-winged Insects)
Twisted-winged insects in the family Stylopidae are endoparasites of short-tongued bees in the families Andrenidae, Colletidae, Halictidae, and Melittidae. In North America, there are five genera, and each species within those genera typically has a specific bee host. Infection of the host bee by the parasite begins in the larval stage and continues to the adult bee. The first instar triangulin larvae are present on flowers and in nectaries. According to Danforth et al (2019), only one account exists for how they are transported to the nest: While a bee imbibes nectar from a flower, it also imbibes the triangulin. The bee transports the triangulin back to its nest in its crop, then egurgitates the nectar in a nest brood cell, and at the same time deposits the triangulin in the cell. The mobile triangulin searches for a host egg or larva to infect. It enters the host, then develops in the host. During host pupation, it moves to the abdomen. When the infected bee emerges from the nest as an adult, the twisted-winged insect males leave the host, but the females remain. When the females become fully developed, they begin protruding from the bee's abdomen. Pheromones produced by the female attract males that mate with the females on the host. Females produce first instar larvae that transfer to flowers while the bee visits flowers.
A Stylops female parasitizing an Andrena male.
Participatory Science Opportunity
iNaturalist Project - Predation of Bees
Despite warning colors, stingers, and many other defense mechanisms, bees are no stranger to becoming a meal for another organism trying to survive.
This project is a collection of observed predators of bees around the world. All observations of this project are to be a photo of a bee being predated by any kind of organism (ambush bugs, spiders, birds, skunks...). All are welcomed and encouraged to contribute to the project! :)
Explore Bee Families
Citations and Further Reading
Danforth, B. N., Minckley, R. L., & Neff, J. L. (2019). The solitary bees: biology, evolution, conservation. Princeton University Press.
Davis, S. E., Malfi, R. L., & Roulston, T. A. H. (2015). Species differences in bumblebee immune response predict developmental success of a parasitoid fly. Oecologia, 178, 1017-1032.
Grissell, E. (2007). Torymidae (Hymenoptera: Chalcidoidea) Associated with Bees (Apoidea), with Bee Parasitoids. International Society of Hymenopterists, 16(2), 234-265.
Klimov, P. B., OConnor, B. M., Ochoa, R., Bauchan, G. R., Redford, A., & Scher, J. (2016). Bee mite ID: Bee-associated mite genera of the world. https://idtools.org/bee_mite
Malfi, R. L., Davis, S. E., & T'ai, H. R. (2014). Parasitoid fly induces manipulative grave-digging behaviour differentially across its bumblebee hosts. Animal behaviour, 92, 213-220.
Matthews, R. W., González, J. M., Matthews, J. R., & Deyrup, L. D. (2009). Biology of the parasitoid Melittobia (Hymenoptera: Eulophidae). Annual Review of Entomology, 54(1), 251-266.
Müller, C. B. (1994). Parasitoid induced digging behaviour in bumblebee workers. Animal Behaviour, 48(4), 961-966.
Parker, J. B., & Böving, A. G. (1924). The blister beetle Tricrania sanguinipennis biology, descriptions of different stages, and systematic relationship. Proceedings of the United States National Museum.
Parslow, B. A., Schwarz, M. P., & Stevens, M. I. (2020). Review of the biology and host associations of the wasp genus Gasteruption (Evanioidea: Gasteruptiidae). Zoological Journal of the Linnean Society, 189(4), 1105-1122.
Polidori, C., Scanni, B., Scamoni, E., Giovanetti, M., Andrietti, F., & Paxton, R. J. (2005). Satellite flies (Leucophora personata, Diptera: Anthomyiidae) and other dipteran parasites of the communal bee Andrena agilissima (Hymenoptera: Andrenidae) on the island of Elba, Italy. Journal of Natural History, 39(29), 2745-2758.
Wheeler, A. J. (1997). Notes on mating behavior of Rhipiphorus luteipennis (Coleoptera: Rhipiphoridae). Entomological News, 108(1), 29-33.
Williams, K., Pan, A. D., & Wilson, J. S. (2024). Velvet Ants of North America (Vol. 145). Princeton University Press.
Page Photography and Video Credits
Joel Gardner CC BY-ND-NC 1.0 (Melittidae)
Heather Holm
Don Leaon CC BY-ND-NC 4.0 (Phymata, Crab spider and nematode video)
Michelle Orcutt CC BY-ND-NC 4.0 (Agapostemon mites)