Friday, 6 June 2014

A couple of surveys

I was invited to help with a couple of surveys this week and found some interesting specimens. The first location was a disused mill with associated ponds, dams, millraces and reservoirs. This is a wonderful site covering tens of acres, with old deciduous woodland and various meadows in addition to the water features mentioned above. It was also on limestone, which I always find interesting. Sedge and grass specialists would have a field day here. We were actually hoping for butterflies, but it was dull and wet, so I concentrated on leafmines, which are always there despite the weather.

First interesting specimen was this one on Ground Elder:

Blotch mine on Ground Elder
Most mines are specific to family, perhaps even species of plant, but this is the mine of Phytomyza angelicastri, which is more usually found on Angelica. So this isn't a new mine for me, but it is a new host for that species. I can now add that insect to plant association in my Donegal Wildlife database.

There were a couple of specimens of Early Marsh Orchid in the middle of a path next to one of the ponds:

Early Marsh Orchid
Sawflies are one of the least-studied groups of insects. They are difficult to identify to species, often requiring dissection for a certain identification. The larvae are also poorly documented, and since they can change their appearance dramatically when they shed their skin, identifications are very tricky. One or two species can be identified from photographs, but first you have to eliminate similar-looking Ichneumonids. This is the sawfly Tenthredo livida (male):


The sawfly Tenthredo livida (male)

One of the main characters that can be used to separate Ichneumonids and Sawflies is the microsculpture on the thorax. In this case, it looks like the letter 'M':

Close-up showing microsculpture on the thorax
Ichneumonids tend to have a smoother thorax, although that's not a hard and fast rule.

This Eristalis hoverfly caused me a few id problems.

Eristalis nemorum  (male)
One of the main keying features for these is the facial stripe, which is more or less absent on this specimen. So that immediately keys to Eristalis arbustorum. But this didn't look right for that species. The key caters for specimens of E. arbustorum with a slight facial stripe caused by wear and tear, but this still didn't key out properly until I took into account the very narrow stigma (dark thin line) on the outside edge of the wing. This is a feature of Eristalis nemorum, which I am now told can sometimes be found with no facial stripe. I suspect that some of this variation is caused by the fact that my local specimens are found on acid soil, but this specimen was on lime.

Caddis flies are always found near water, since the larvae live at the bottom of ponds, ditches, etc.
Caddis Fly

Shield Bugs, in common with all other Heteroptera, go through a series of nymph stages before becoming adult. In each stage they become slightly more like the adult in size and pattern. This appears to be a final-instar (full-size, with larger wing-cases) nymph of Pentatoma rufipes:
Final instar nymph of the shieldbug Pentatoma rufipes
 There was a family of Mute Swans on one of the mill ponds:
Mute Swan and cygnets
I wouldn't normally go near swans with cygnets, but I was advised that this pair were calm enough. The male quickly got between me and the family and hissed a bit, but stayed to the side, watching me until he saw that I was just taking photographs. Interestingly enough, this is new to my species list.

All in all a lovely location that I will revisit in the future.

2 comments:

amanda peters said...

After reading your last post on Glenarm Bioblitz, I was interested in you enthusiasm for the Leafmining fly (Cerodontha silvatica) how great is the importance of these very small and over looked family of flies. You have mentioned them again in this post as well... Because I have been thinking about it, I have noticed more evidence of Leafmining on the plants at the park, especially on one of the Oak trees.

stuart dunlop said...

@Amanda: there are 4 groups of insects that make leaf mines in our area: flies, micromoths, sawflies and weevils. Mining species usually stick to a family of plants, so if you know the plant, you can eliminate 95% of potential id's. I have documented around 70 species of miner, and you can find them here:

http://donegalwildlife.altervista.org/leaf-miners.htm