Ocean Mist

Posted by Jes

Crabtree Reserve Report


Note: Click on table for enlarged view.

The butterflies on Crabtree Reserve Lullybeg are counted by walking the transect route on part of the reserve from April to the first week in October. These results are sent to the National Biodiversity Data Centre. Butterflies seen outside the transect route are counted separately. Both counts are reflected in the table; the figure outside the brackets representing all butterflies counted while figures inside the brackets are transect counts.

The figures for 2015 are heavily influenced by a fire that occurred during sunny weather in April. The fire was a hot fire, burning slowly in calm weather. At the time, hundreds, possibly thousands of Marsh Fritillary larvae were present so the incident could scarcely have occurred at a worse time for the butterfly. The site contained a build up of highly flammable senescent vegetation which burned very well and destroyed the larvae basking on it. The fire was extinguished mainly by burning itself out. Subsequent counts found few larvae. Instead of the hundreds of adults we expected before the fire, we counted 32 individuals during the flight period, mainly in June. Happily, the site vegetation, including the Marsh Fritillary larval host plant, the Devil’s-bit Scabious was recovering at this stage. Autumn searches resulted in the location of just five larval webs, down from 37 larval webs found during the previous autumn. However, this reduction is not expected to hamper the species’ recovery; all five webs contained large numbers of larvae and all were in favourable situations. In addition, it appears that a population that was present at nearby Lullymore may have moved to Lullybeg. A strong population that bred on good habitat in Lullymore in 2013 and 2014 was not found there this year, even though favourable habitat persists. There is evidence in literature that Marsh Fritillary colonies move from time to time. This habit underlines the need to conserve nearby habitats and maintain a suitable open landscape in order to maintain habitat networks and allow for population movement and dispersal.

The fire is also likely to have destroyed basking Silver-washed Fritillary larvae too and while the larvae of other species such as the brown family of butterflies were also present at this time, these are likely to be less vulnerable; in spring these larvae feed mainly at night, keeping low down in contact with damp mosses and green vegetation during the day.

Interestingly, the Dingy Skipper, likely to have pupated or to be in a pre-pupation stage by early April (this takes place on or close to the ground) seems to have been little affected. The table indicates that the butterfly had its best year on the site since we began systematic counts.

While chance events will impact on populations occasionally weather influences populations every year. The improvement in the summer weather in 2013 and 2014 was interrupted in 2015 with particularly disappointing weather during May, July and August. Dramatic declines in Ringlet and notable falls in Meadow Brown, Speckled Wood and Small Heath numbers were noted, although the Speckled Wood’s reduced count is linked to an area (on the site but outside the transect route) highly favoured by the butterfly in previous years being unvisited due to invasion by brambles. The Wall Brown had another bad year, continuing a national trend of low numbers.

Like the Wall Brown the Dark Green Fritillary was represented by one sighting. The Brimstone, together with the Dingy Skipper had its best year since these counts commenced. The Large White, Common Blue, Small Copper, Small Tortoiseshell and Painted Lady were up on 2014’s figures but all the other species had lower numbers.

By the season’s close the site has recovered, and a great deal of habitat maintenance work is planned, particularly for the southern side; this will mainly consist of scrub control/removal and substrate disturbance and will be carried out by Bord na Móna staff using machinery.  These operations will assist in maintaining the habitats needed by the reserve’s butterflies and moths.

We offer our gratitude to all of our members and supporters including Bord na Móna for looking after this site, a major biodiversity hotspot in Ireland’s midlands.