SWARMING IN A BALLOON-CARRYING EMPIDID 
(EMPIDIDAE: HILARA )' 
By T. G. Forrest 
Dept, of Entomology and Nematology, University of Florida, 
Gainesville, Florida 32611 
Introduction 
Swarms are perhaps the most spectacular of insect mating aggre- 
gations. Usually groups of males fly at particular stations or 
markers where females come to locate mates (Sullivan 1981). 
Swarming behavior is particularly common in Diptera, the flies. In 
one family, the Empididae, it is especially well known because 
swarming males often carry gifts of prey which are presented to 
females during copulation (i.e. nuptial feeding, Downes 1969). The 
gift-giving has become ritualized in some empidids and “balloons” 
made of glandular secretions produced by males are transferred to 
females at coupling (Kessel 1955). Balloon flies are found among 
three genera of empidids ( Empimorpha , Empis, Hilara ). 
Though a large and diverse group of flies, few species of empidids 
have been extensively studied in the field (Alcock 1973, Chvala 
1976). In North America only five balloon-carrying species have 
been studied (Kessel 1959) and all occur in western United States 
and Canada. This report is the most extensive of the field studies of 
the swarming and mating behavior of a single species of balloon fly 
and is the first detailed study of a balloon fly from the eastern U.S. 
Materials and Methods 
The study site was the edge of a 50 X 100 m wooded area adjacent 
to cultivated fields at Green Acres Farm, Dept, of Agronomy, Uni- 
versity of Florida (NE 1/4, sec. 27, tp. R18E, T9S). Adult season in 
Gainesville lasts about 2 weeks during late March or early April. I 
'Dr. Paul H. Arnaud, Jr. has examined specimens and determined this to be a new 
species of balloon fly. Voucher specimens have been deposited at the California 
Academy of Sciences, San Francisco and the Florida State Collection of Arthropods, 
Gainesville. 
Manuscript received by the editor January 10, 1985. 
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