Crataerina pallida
In 3 days ~10% in a week ~20%
Crataerina pallida, the swift lousefly, is a species of biting fly in the family of louse flies Hippoboscidae. These flies are commonly encountered in the nests of the common swift (Apus apus) in Europe and Asia. The lousefly spends its entire life cycle associated with swifts. The adult lousefly produce larvae in the late summer months which then pupate and lie dormant during the winter months inside the vacated swift nest. These parasites have highly aggregated population distribution and high levels of host prevalence. The adult fly then hatch out in spring when the first swift eggs are laid, by the returning adults, and feed on the blood of the nestlings and the adults, sucking about 25 mg of blood every 5 days. They can be a serious pest of adult and nestling swifts.
Crataerina pallida is a vertically transmitted ectoparasite, in that it is passed from parent host to offspring. C. pallida are relatively benign, because their own species' fitness will depend on successful reproduction of swifts. Evidence suggests that C. pallida had little if any effect on nestling growth or fledging success rate. Wikipedia →
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More parks will be added in future updates.
Rare
Under 5% of wildlife watchers report a Swift Lousefly sighting in Vienna on a given day, based on 6 verified sightings from GBIF citizen-science data. It is the 1286th most-seen of the 1406 insects we can rate there. Over three days the chance rises to about 10%, and over a week to about 20%, if each day is a fresh chance.
Any time of year
In every month with enough records, under 5% of wildlife watchers report a Swift Lousefly in Vienna on a given day, so our monthly data shows no clear season.
Among the best
Of the 3 cities where we can rate Swift Lousefly sightings, Vienna ranks 2nd at under 5%, level with the leaders once rounded. The best odds are in Helsinki (Finland, under 5%).
Same order: Diptera
The closest relatives of the Swift Lousefly that you can see in Vienna (order Diptera, Flies) are Marmalade Hover Fly (about 20%), Hornet Mimic Hover Fly (about 10%) and Common Drone Fly (about 10%), with each one's daily chance of a sighting.
GBIF citizen-science records
It is estimated from how often the Swift Lousefly is recorded against all the insects logged in Vienna (6 verified sightings), calibrated against known sighting rates. Figures are rounded to the nearest 10% because citizen-science data supports honest approximations, not decimals, and months with records from fewer than five people show "—". How it works.
