North America
In North America, P. rudis eggs generally require 27–39 days to fully develop into an adult. In Canada, 25–30 days are required when the temperature is 23°C, and 11-14 of these days are spent in the pupal stage. Cluster flies in North America overwinter in their adult stage, and copulation takes place in the spring. There are three species in the rudis species complex of North America, and the life cycle of each species may differ. The variety of species in North America may account for the discrepancies between European and North American cluster flies life cycles.
Female cluster flies preferentially oviposit eggs in humid areas with dense surface vegetation and high soil moisture. Each egg is either deposited by itself or in a small cluster of about seven eggs. In total, a female cluster fly will lay an average of 100-130 eggs by ovipositing a small group, then crawling or flying some distance before ovipositing each subsequent group of eggs. Once the larvae hatch, they burrow into the soil by following natural pore spaces, such as holes near plant stems or paths that earthworms have already created. By randomly moving though these pores, P. rudis larvae find their host worms. A larva is prompted to penetrate an earthworm when it senses “penetration inducing factor,” a substance that is present in the slime and coelomic fluid of an earthworm. The larvae then use their mandibles to penetrate the dorsal side of a worm. It is important that they find their host quickly, because larvae must penetrate a worm within three days in order to survive.
More than one larva can penetrate a single earthworm, and two or more larvae can share a penetration site. Once the host worm begins to decompose and is no longer useful to the larvae, the larvae can either leave to find another host or move to a less decomposed section further down on its host worm. If a first instar larva decides to move to another host, it must penetrate its new host quickly in order to survive. Towards the end of the first instar stage and into the second and third instar stages, the larvae are able to survive longer separations from their hosts. Usually, the first and second instars act as internal parasites while the third instar can parasitize the host and feed on the surface of the host. Currently there are no reports of P. rudis reducing earthworm populations or causing horticultural problems.
Read more about this topic: Pollenia Rudis, Life Cycle
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