Vol. xxv] ENTOMOLOGICAL NEWS. 73 
and inconvenient flowers. It would be distinctly disadvantage- 
ous for it to limit itself to some particular flowers and exceed- 
ingly unlikely that it would do so. The ecological specializa- 
tion exhibited by Anthedon, Verbenapis and other oligotropes 
is a fairly certain indication of the pressure of competition. 
I think that the long-tongued pygidial bees were developed 
as competitors of the bumblebees, the first on the ground and 
the most polytropic of bees. I think this explains why they 
have a comparatively short and rapid flight and so frequently 
oligotropic habits. In a similar way the Andrenidae, Panur- 
gidae and related groups which are so often oligotropic were 
probably preceded by the Halictidae, the most polytropic of 
short-tongued bees. There are forty species of Halictidae fly- 
ing throughout the season. In the spring there are the females 
which have passed through the winter, but later both sexes of 
the regular brood are flying so that the maximum is late. There 
are ninety-four other short-tongued bees occupying the same 
region. It would be a hard matter for all of these bees to fly 
throughout the season and compete with the Halictidae. In- 
stead they have short times of flight and are distributed 
so that not more than fifty-two are flying in any month 
and these only in the spring when the Halictidae are least 
abundant. Amd these bees are the least abundant when the 
Halictidae are the most abundant and most active. The early 
maximum, the short flight, the non-competitive phenological 
distribution, and the frequently oligotropic habits indicate that 
these bees have managed to hold their own only by dividing 
up the remaining field and occupying the most favorable cor- 
ners left by their perennial polytropic competitors. 
To the list of local oligotropes add: Petalostemon viola- 
ceus: Colletes albescens, robertsonii; Strophostyles angulosa: 
Megachile strophostylis; Papilionaceae: Meg. generosa, 
Gnathodon georgicus, Anthidium psoraleae, Synalonia atri- 
ventris, fuscipes; Salix: Andrena salicacea, macoupinensis ; 
Nymphaeaceae: Chloralictus nymphaearum; Cassia chamae- 
crista: Melissodes atripes; Ipomoea pandurata: Cemolobus 
ipomoeae. 
