Chirosia betuleti
In 3 days ~10% in a week ~20%
Chirosia betuleti is a species of fly, which causes knotting gall in ferns. The gall develops in the terminal shoots of ferns, such as broad buckler fern (Dryopteris dilatata), male fern (Dryopteris filix-mas), lady fern (Athyrium filix-femina), and ostrich fern (Matteuccia struthiopteris).
The fly larva mines the leaves and stems of the fern's frond at the apex. The tip of the frond rolls upwards into a loose, obvious knot or mop-head structure involving many pinnae; inside, a white larva mines along the rachis, eating the trichomes, causing it to coil. Usually, only one larva is present in the leaf tip, sometimes two. An elongated white egg shell is visible at the centre of the mass.
Eggs are laid in the unfurling fronds and the hatched larvae feed on the trichomes in the groove of the rachis, causing the frond to curl inwards. The pupae drop from the gall and remain from autumn and winter to emerge in the spring. Galling rates up to nine fronds in 13 on a single plant have been noted.
The knotting gall is found in Cornwall, Wiltshire, Worcester, Hants, Norfolk, Warwickshire, Berkshire, Cardiganshire, Cheshire... Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|
More parks will be added in future updates.
| # | City | Country | Daily sighting probability |
|---|---|---|---|
| 1 | London | 🇬🇧 United Kingdom |
Rare
Under 5% of wildlife watchers report a Knotting Gall sighting in London on a given day, based on 7 verified sightings from GBIF citizen-science data. It is the 1219th most-seen of the 1504 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 Knotting Gall in London on a given day, so our monthly data shows no clear season.
Only London, in our data
London is the only city on Wallace's Line with enough records to rate Knotting Gall sightings: under 5% of wildlife watchers there report one on a given day.
GBIF citizen-science records
It is estimated from how often the Knotting Gall is recorded against all the insects logged in London (7 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.
