Dagger flies Mating. Filmed in Sami Dino Parkı, Ferahevler, İstanbul on May 12th 2015.
Male hilarine flies (Diptera: Empididae: Empidinae) present their mates with silk-wrapped gifts. The nuptial gift keeps the female busy during copulation. The silk around the gift is produced by specialized cells located in the foreleg basitarsus of the male fly. Here in this observation the hind legs of the male appear to have multiple functions: They form a resting platform for the female and at the same time also interfere with how the female interacts with the nuptial gift by contributing to the rotational movement of the gift ball. Some dagger fly males “re-use” their nuptial gifts for another female. Therefore the male probably doesn’t want to let his gift go. While the forelegs of the male hold onto the leaf edge the middle pair continuously move in an interactive fashion stroking the bristles of the female thorax. The following TED Talk by Marlene Zuk describes the evolutionary significance of nuptial gift in insects with a specific example from crickets:
In the insect family of Diptera nuptial gift may have a complex chemistry. In malaria transmitting mosquitoes (Anopheles gambiae) a steroid hormone is packaged inside a “mating plug” similar to nuptial gift. There’s one difference however. Nuptial gift is presented before mating. A mating plug on the other hand is a gelatinous substance presented to the female after mating. The hormone 20E triggers female mosquitoes to lay eggs. This has a rather cool sounding technical name Mating-Induced Stimulator of Oogenesis (MISO).
In order for a female mosquito to become reproductively active and lay eggs, she must first eat a blood meal. Once she fills her appetite with protein rich blood she will be ready for a mate. During mating in order to trigger egg development male must pass the female a mating plug containing the steroid hormone 20E at the end of copulation. Understanding the mating system of mosquitoes can help prevent malaria which kills 600 thousand people every year.
Another mating event of dagger flies was also recorded in almost half a world away from Turkey: in Japan. In late May of 2012 a pair of empidid dance flies (a.k.a. balloon flies or dagger flies; Empis (Polyblepharis) sp., family Empididae) were filmed while mating on a twig beside a mountain stream. The copulation took place in a typical “courtship feeding” fashion while the female consumed the nuptial gift. According to my fellow Japanese observer friend the prey item appeared to be a mayfly (unidentified, order Ephemeroptera). My friend also reported that as soon as the female finished feeding on the prey, she dropped the leftover to separate from the male. Note that only the female has black hairs on the legs which is something observed in sexually dimorphic species.
Additionally, these predatory flies can also serve as pollinators. Their long proboscis adapted to pierce prey can also reach into deep flowers enabling them to feed on floral nectar. This behavior was documented at a park in Istanbul where a dagger fly was recorded pollinating a common mallow (Malva neglecta).
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