Cogden by the sea

(updated, now that I have seen the specimens under a microscope! ;))

Today’s jaunt was to Cogden beach (Dorset, SY502881) to pick up a bit of the sea air and have a look at the coastal flora. We got out early to get into the carpark before it filled up and headed down to the path behind the shingle. The sun beat down but the wind was brisk enough to keep the temperature nice and comfortable.

The flora is dominated by Thrift, Sea Campion and Sea Kale but later in the season there are other interesting things. Bird life was limited to 100s of Whitethroats and Chiff-Chaffs; a pair of Linnets and a very noisy Cetti’s Warbler that refused to show itself, as usual.

Despite the site having plenty of promise I had never managed to find much in the way of insect life in the past, but today I noticed a lot of Brown-tail and Lackey moth tent nests and this intrigued me enough to catch my attention for most of the visit. Both moth species attract some very interesting parasitoids so I was keen to see if any tachinids showed any interest in the webs. I didn’t have to wait long before I spotted a few and they look a new species for me:

Observations: Attention was drawn to a Lackey moth larval nest when we spotted the (3rd-instar?) larvae thrashing around, whipping their heads from side to side in classic “anti-parasitoid” behaviour. On closer examination a few hunch-backed grey flies with orange legs were seen wandering over the web and paying particular interest to the larvae. The flies were very easy to catch as they never once took flight and would walk slowly but determinedly around, sidling up to individual larvae and occasionally arching their abdomens forward. I couldn’t see eggs being laid but it seemed clear that they were laid on or very close to the larvae and not just scattered on the web.

On returning home I dashed through the door and chucked a specimen under the microscope to finally see what it was. Although I had been hoping that they might be Townsendiellomyia nidicola (a very rare Brown-tail parasitoid), lurking at the back of my mind was the thought that they were siphonines (due the their hunch-backed appearance & colour) but there was no long, hinged proboscis so they couldn’t have been Siphona. Sure enough, under the microscope the long sub-apical scutellars were converging and vein r4+5 was hairy and it keyed to Goniocera versicolor, another extremely rare tachinid, known in the UK from scattered records across southern England with most modern records in south Wales. The clincher this time is that the host is Lackey moth, which fitted my observations perfectly.

* thanks to Mick Parker for the Lackey moth identification 🙂

3 Replies to “Cogden by the sea”

  1. Chris, not sure if I’m misunderstanding you here, but I don’t see any evidence of Brown-tail, the larvae in the webs are Lackey too aren’t they? Is that a new host record as well?

  2. @kitenet
    Hi Martin, yes it was a bit of early confusion caused by the fact that there were both species at the site and I had just assumed that these must be the Brown-tail/Townsendiellomyia pair … when actually I found out later that they were Lackey/Goniocera 🙂 Mick Parker also spotted the ‘wrong’ larvae and that made me pay more attention to certain doubts that I had about the tachinid 😉

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