Just as the majority of New York City’s bees nest in the soil, most, or 151 species, live a solitary and/or communal existence. In solitary species, a reproductive female constructs a nest, provisions it with pollen, lays eggs, and then leaves. After that, the larvae are on their own—there is no further care or provisioning from the mother. Some solitary bees construct nests near other nests (termed “aggregations”) or even share a single nest (called “communal”). Species with aggregations or communal nests, however, are still considered solitary if the reproductive females provide no further care after the initial provisioning of the nests with pollen. Solitary bees include miner bees (genus Andrena, 58 species), leaf-cutter bees (genus Megachile, 18 species), mason bees (genus Osmia, 26 species), masked bees (genus Hylaeus, 11 species), long-horned bees (genus Melissodes, 9 species), plasterer bees (genus Colletes, 7 species; note that plasterer bees are considered solitary because each female builds her own nest for rearing young, although they often form aggregations where many nests are close to each other), small sweat bees (genus Lasioglossum, 6 species; note, however, that some small sweat bees species are primitively eusocial—see below for details), and small carpenter bees (genus Ceratina, 3 species).
The solitary lifestyle contrasts with the behavior of “subsocial” species—four in New York City— in which the mother continues to feed the larvae as they develop, a progressive step towards greater social interaction. Subsocial species in the city include the large Eastern Carpenter Bee (Xylocopa virginica), and three much rarer bees: Pseudopanurgus compositarum (Family Andrenidae), Ptilothrix bombiformis (Family Apidae), and Svastra oblique (Family Apidae). There are other types of social behavior in bees as well, such as “parasocial,” “quasisocial,” “semisocial,” and even “sleeping aggregations.” For more information about these, see The Social Behavior of the Bees: A Comparative Study by Charles Michener, which is available for free via Google Books.
Fifteen percent of New York City’s bee species are termed “eusocial” because they exhibit much more complex social behavior, including physically differentiated castes such as workers, drones, and queens that contribute in different ways to the well-being of the colony by foraging, for example, or reproducing. Bumble bees (genus Bombus, 11 species), some small sweat bees (genus Lasioglossum, 19 species), and some green metallic bees (genus Halictus, 3 species) are classified as “primitively eusocial” because colonies are not perennial—all individuals die in the fall except for the new queens who hibernate and then create new colonies in the spring. European honey bees are the only species classified as “advanced eusocial” because the colonies are perennial and there is greater differentiation in the physical attributes of the castes.
Three species of bee in New York City exhibit a specific type of cleptoparasitism called “social cleptoparasitism.” In these species, a female enters the nest and kills the queen of the social host species in addition to any developing larvae. She then lays eggs and effectively becomes the new queen of the colony. Workers of the host species care for the developing young of the parasitic species. Social parasites include the common Lemon Cuckoo Bumble Bee (Bombus citrinus), which parasitizes the nests of other bumble bee species, and the somewhat rarer Lasioglossum cephalotes and Lasioglossum platyparium, which both parasitize other small sweat bees.