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1. The time that pairs of the dance fly Ernpis borealis (L.) (Diptera: Empididae) spent in copula was positively correlated with the volume of the nuptial gift.2. In some cases the copulation duration was short although prey volume waslarge. Females engaged in these rnatings had more worn wings, were therefore older, and most probably had sperm already stored in the spermatheca. It is suggested that these copulations were interrupted because either the spermatheca was full of sperm and the male was not able to transmit any sperm, or because prey content was depleted (males may have fed on the prey or the prey had been used in a previous mating). The latter explanation seerned more probable.3. A male providing a large nuptial gift may transfer larger quantities of sperm. Quantitative sperm competition is mcre likely than last-male sperm predominance.

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