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Mission, Texas

Stelis costalis; cuckoo bee; Copyright 2023 Sharp-Eatman Nature Photography


Tribe Anthidiini - Genus Stelis

The genus Stelis belongs to the same bee tribe (Anthidiini) as the Dianthidium shown earlier in this guide.  Stelis are cleptoparasitic cuckoo bees that are small-to-moderate sized (4-14 mm), and usually black, or a dark metallic blue or green.  Their bodies tend to be heavily pitted, and they often have yellow or white patterns on their abdomens; some have reddish-orange abdominal markings, and some have colorful markings on the face and thorax as well as the abdomen. 


Stelis share traits typical of other Anthidiini:  they have forewings with two submarginal cells and arolia on their feet – female Stelis, however, lack scopal hairs under their abdomens because, like other cuckoo bees, they do not gather pollen but instead rely on the pollen stores of their hosts.

Bee behavior

Stelis of the Western Hemisphere primarily target the nests of other Megachilinae, among them members of the tribes Osmiini, Megachilini, and even their own tribe, Anthidiini.  Stelis (Dolichostelis) target resin bees of the subgenus Megachile (Chelostomoides). 

Most Stelis enter their hosts’ nests while the hosts are still in the process of building their egg chambers, before the cells are sealed.  The cuckoo larvae that later hatch use their mandibles to destroy the hosts’ eggs or larvae and then devour pollen stores left behind by the host.  Bees of the subgenus Stelis (Dolichostelis), however, such as the ribbed Stelis, operate differently.  Stelis (Dolichostelis) are  “closed-cell parasites,” that is, they break into their hosts’ nests after the egg chambers are sealed.  The cuckoo bees then dispatch the hosts’ eggs and replace them with Stelis eggs.   

Stelis costalis; cuckoo bee;  Copyright 2022 Sharp-Eatman Nature Photography

A female Stelis costalis


Order:   Hymenoptera

Family:   Megachilidae

Subfamily:   Megachilinae

Tribe:  Anthidiini

Genus:  Stelis

Species shown on this page:  
    Stelis (Dolichostelis) costalis

      (ribbed stelis cuckoo bee)

Associated plants: 

Hairy wedelia

(Wedelia acapulcensis var. hispida)

Family: Asteraceae

​When and where seen:  

June 6, 2021

(Cameron County)

Ribbed stelis cuckoo bee

Stelis (Dolichostelis) costalis 

Family:  Megachilidae

Size:   9 mm  (female)

           8 mm (male)

Stelis costalis; copyright 2023 Sharp-Eatman Nature Photography

A female Stelis costalis

Stelis costalis is very similar to, and often confused with, the more widespread Stelis (Dolichostelis) louisae.  The color patterns on the two species are nearly identical.  According to John L. Neff, Director of the Central Texas Melittological Institute, the two species  are best separated by viewing a trait evident only under magnification:  the density of pitting on the bee’s gena (cheek) -- on Stelis costalis, punctures on the gena nearly touch one another, while on S. louisae there are larger, shiny interspaces between the pits. 


The geographical ranges of these two species within the United States just barely overlap and differ widely:  while Stelis costalis has a restricted range centered in southern Texas, S. louisae is widespread throughout the eastern half of the United States, from east Texas and Nebraska to the Atlantic Coast, as far North as Maine and as far South as south Florida.

Stelis Species of the Lower Rio Grand Valley

CITE THIS PAGE:  Sharp, Paula and Ross Eatman.  "Stelis."  Wild Bees of the National Butterfly Center of Mission, Texas. 15 Jan. 2019,  Accessed [day/month/year guide accessed].

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