Glossosomatidae Family - ID Tips
Class: Insecta; Order: Trichoptera; Suborder: Spicipalpia; Family: Glossosomatidae
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Vital Stats |
Rating |
Scale |
|
BMWP Score |
7/10 |
1 = Filthy to 10 = pristine |
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LIFE Flow Group |
2/6 |
1= Rapid velocity (>100cm/sec) to 6= drought resistant |
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Family Level Difficulty Rating |
2/10 |
1= Easy to 10= very difficult |
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Species Level Difficulty Rating |
6/10 |
1= Easy to 10= very difficult |
Glossosomatidae are cased caddis fly, the larvae have a distinctive case made of rock fragments, humped on the upper side, flat underneath, with an opening at both ends. The British Glossosomatidae family contains two genera, Glossosoma and Agapetus. They are encountered in clean fast flowing rivers and are absent from still and polluted waters.
Identification
The key to case bearing caddis larvae (Wallace et al, 2003) has a good description and drawings of all the features described below, but these additional photos should help with understanding what they look like on a real specimen and help to locate the features described.
The genus Agapetus is easily separated from Glossosoma by the presence of sclerites on the mesodorsum and metadorsum. The identification can also be confirmed by the presence of a number of hairs on each side of the pronotum, up to 7 on the anterior margin of Glossosoma and more than 7 for Agapetus.
Agapetus with a head width under 0.3mm can not be identified and must be left as Agapetus sp. If the head width is over 0.3mm, then unless damaged, it should be possible to identify the species. There are three species in the genus Agapetus; Agapetus fuscipes, Agapetus ochripes and Agapetus delicatulus.
Agapetus fuscipes has the largest metadorsal sclerites, with a maximum dimension over half the distance between the two setae next to the sclerites on the metadorsum, see image below.
Agapetus ochripesand delictulus have smaller metadorsal sclerites, with the maximum dimension about half the distance between the setae in A.ochripes (see photo below) and less than half the distance in A.delicatulus.
As this can be difficult to measure sometimes there are a number of other features given in the key which should also be checked to confirm identification. The lateral setae are a very useful feature provided the setae haven’t been damaged or fallen off, and the correct row of setae is checked. Follow the line of setae which runs along the abdomen from the 3rd leg towards the end of the body. In Agapetus fuscipes there is a prominent lateral setae on the 3rd abdominal segment, whereas for Agapetus delicatulus and A.ochripes, the setae on the 3rd abdominal segment is missing. An example with and without this seta on the 3rd abdominal segement is shown below.
On the 8th abdominal segment, the posterior lateral setae can be used for identification. In Agapetus fuscipes they are as conspicuous as the other two large setae visible in the photo. In both A.ochripes and A.delicatulus this seta is pale and inconspicuous, or as in the example photo cannot be seen.
A final feature you can check is the mark where the leg joins the pronotum. There are good drawings and descriptions of this mark for all three species in the key. The photos below show this feature for Agapetus fuscpies and Agapetus ochripes.
Identification of Synagapetus dubitans - SPECIES NEWLY FOUND IN THE UK
Synagapetus, like the Agapetus genus can be separated from Glossoma by the presence of sclerites on the mesodorsum and metadorsum.
To separate Synagapetus dubitans from the British species of Agapetus a number of features need to be checked. As in Agapetus fuscipes, there is usually a lateral seta present on the third abdominal segment, this distinguishes it from A. ochripes and A.delicatulus. The lateral saetae on the 3rd abdominal segment may be missing in S. dubitans, in which case the ventral setae can be used. In all three british species there are no ventral setae on the 6th and 7th abdominal segment, in S. dubitans both setae are present. See pictures in Pitch, 1993. The metadorsal sclerites of S. dubitans are smaller than those of A. fuscipes, more similar to A. ochripes. The rear margin of the pronotum has a dark line, which in S. dubitans reaches or very nearly reaches the middle suture, whereas in A. fuscipes, the line is about half this length and stops well before the middle suture. Pictures are given in the key by Pitch, 1993
References
Wallace, I.D., Wallace, B and Philipson, G.N. (2003) Keys to the case-bearing caddis larvae of Britain and Ireland. Freshwater Biological Association. Scientific publication 61.
Pitsch, T (1993) Zur Larvaltaxonomie, Faunistik und Ökologie mitteleuropäischer Fließwasser-Köcherfliegen (Insecta: Trichoptera). Technische Universität Berlin http://opus.kobv.de/tuberlin/volltexte/2009/1956/pdf/pitsch_thomas.pdf
