Bembix sayi
Cresson, 1865
sand wasp
Bembix sayi is a of sand wasp in the Crabronidae, found in Central America and North America. Like other members of the , it is a solitary that excavates burrows in sandy substrates and provisions nests with paralyzed flies for its larvae. The species exhibits , where females continue to supply food as the larva grows.
Pronunciation
How to pronounce Bembix sayi: //ˈbɛmbɪks ˈsɪ.aɪ//
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Habitat
Deep, dry sand barrens and sandy exposures with loose, deep sand. Observed in sand prairie and dune environments.
Distribution
Central America and North America. Documented in the United States (including Colorado, New Mexico, Missouri) and extending south through Central America.
Seasonality
Active in spring and fall; observed nesting in August and early autumn. Likely has two annually with as .
Diet
feed on flower nectar, particularly from composite flowers (Asteraceae). Larvae are provisioned with true flies (Diptera, excluding ), which are paralyzed or killed by the female's sting.
Life Cycle
Females excavate oblique, nearly horizontal burrows 19-57 cm long and 5-28 cm deep in sand, often with short dead-end burrows nearby to confuse . An is laid on the first prey item or in the empty before hunting begins. continues as the larva grows, with up to twenty flies supplied per larva. The larva spins an oblong cocoon incorporating sand grains, as a .
Behavior
Females use a 'tarsal rake' of spines on the front legs to rapidly excavate sand during burrow construction. They employ subtle landmarks to locate concealed burrow entrances when returning with prey. Males participate in 'sun dances'—erratic 1-2 inches above ground to detect emerging virgin females. Both sexes are fast-moving and rarely perch for long periods.
Ecological Role
of flies, contributing to regulation of dipteran . Serves as prey for nest including cuckoo wasps (Chrysididae), velvet ants (Mutillidae), satellite flies (Sarcophagidae), and bee flies (Bombyliidae). may be parasitized by thick-headed flies (Conopidae) or killed by robber flies (Asilidae).
Human Relevance
Generally not aggressive toward humans; stings are not dangerously venomous to healthy individuals. May be encountered in sandy recreational areas such as beaches and playgrounds.
Similar Taxa
- Bembix americanaAlso common on sand exposures and shares similar burrowing ; distinguished by subspecific variation in coloration and distribution patterns.
- Other Bembix speciesTwenty-one occur in North America north of Mexico; identification to species often requires examination of morphological details not visible in field observations.
More Details
Nesting aggregation dynamics
Females may construct one or two additional branching from the main burrow after the first larva matures, or fill in the burrow entirely.
Taxonomic history
Formerly placed in Sphecidae; now classified in Crabronidae (or Bembicidae in some treatments) based on phylogenetic revisions.