During 2011 a transect along 500 metres of boardwalk at Hickling NNR was checked from 21st June to 15th August 2011 for Swallowtail Papilio machaon britannicus eggs and larvae in the reedbed fringes, one metre either side of the boardwalk.
This was not intended to be a scientific study, but purely an observational exercise brought about by a comment from the warden: 'Had I seen any swallowtail eggs?'
What ensued was an almost daily check on the number of larvae and eggs found on the Milk Parsley Peucedanum palustre from July to August. However, this article is not based on the numbers of eggs and larvae present, but on observations of events that occurred during the time of monitoring the eggs and larvae along the section of boardwalk.
Overview for Papilio machaon britannicus at Hickling in 2011
Due to a very warm spell towards the end of April, the first swallowtail had been recorded at Hickling on the 25th April. Although this relates to a very early individual, swallowtails began to appear earlier than the normal expected emergence time and in 2011 there was a second brood, which began towards the end of July and continued into August, with adults being seen until 15th August, when a single final instar larvae was also found.
Two eggs were found 22nd June, followed by 5 eggs and 9 1st instar larvae 29th June. In most instances, there was usually only one larvae per milk parsley plant. However, on the 6th July 5 larvae (1st and 2nd instars) were found on just one plant, followed by 3 larvae on another single plant on the 8th July. The numbers of eggs and larvae along the study area remained fairly constant throughout, allowing for developmental changes.
Predation of larvae by Picromerus bidens
During a check on the number of eggs and larvae (9th July), a 1st instar larvae was found dead on a milk parsley plant. On closer inspection a heteropteran species was seen next to the dead larvae. Although it was not clear at the time, whether or not the larvae had been killed by the bug, further evidence was found two days later.
On the 11th July, just behind Cadbury's hide (outside the study area) another swallowtail larvae was found dead, this time a final instar. Once again, the same bug species was found in attendance (see Figures 1 & 2). The bug was later identified as an immature Picromerus bidens. However, this was not the only intriguing factor, as the larvae was feeding on Fennel Foeniculum vulgare. Although there are only a few fennel plants on the reserve (apparently originating from a former wardens herb garden), the plant had been selected by an adult swallowtail, in the absence of any 'preferred' plant species as there are no milk parsley growing anywhere near the area where the fennel was growing. It is also quite clear that the plant sufficiently sustained the larvae through to final instar.