Steninae
Stenus guttula © Roy Anderson. Only Dianous and 5 species of Stenus have orange spots on the elytra.
These are one of the easiest staphylinid subfamilies to recognise, principally on account of their very large and prominent eyes. The 75 British and Irish species are divided into two genera: 74 species of Stenus, plus Dianous coerulescens which you’ll probably only find by specifically searching beside waterfalls and fast water.
The new (June 2011) RES Handbook on Staphylinidae includes new keys to Steninae by Roy Anderson: buy it here. I have now taken the test keys down from this website.
I have found the genitalia illustrations of Steninae by Wüsthoff (1934) to be a great help, and even after the publication of Roy’s new keys, it will continue to be useful, if only to those on the look-out for species new to Britain. With Roy’s help, I have updated Wüsthoff’s nomenclature and a 7MB PDF file is available online or email me for a copy.
12 Responses “Steninae”
re distributions:
Both Stenus oscillator and Dianous have been recorded in Warwickshire. The former from Sutton Park in the north-west of the county from the edge of a heathy mere (SP0998)in 1988, 1997 (SALane) and 2009 (RBooth) and Dianous from a woodland stream right down in the south of the county in company with Stenus guynemeri (Whichford Wood SP3034) 1997 and 1998 (SALane, DJMann).
Records are with the scheme (Jonty Denton).
Subgenus keys now very much better than Tottenham. Very helpful to have diagrams, especially for the intermediate tarsal cases. Whether a tarsus is bilobed, or whether the abdomen bordered, is often a matter of how closely you look! In the final keys it would be helpful to illustrate Tottenhams ’4 keels at base of sternites’ character which I have never understood or seen!
Hemistenus key:
several problems with Stenus ossium
To separate ossium from subaeneus, I tend to look at the punctation of the later abdominal tergites. In ossium, the punctures are definitely finer (though I wouldn’t say particularly closer) than in subaeneus and the tergites very much less shiny. In fact, I can see reticulation on all of my dozen or so ossium specimen tergites, a fact that is at odds with the key which puts ossium clearly into species without micro-reticulation on tergites (couplet 2).
My three dissected male specimens of ossium all have parameres far outreaching the tip of the aedeagus (according well with the illustration in Tottenham) but not looking anything like the two figured aedeagi in the test key. In fact, my dissected aedeagi closely resemble that figured in the test key on page 16 under the name palustris!
Hypostenus key (quite a few issues here):
couplet 3, second option – ‘both first and second antennal segments brown to black’ doesn’t work for tarsalis and oscillator which only have the 1st segment black, but which necessarily have to key out here. I would personally just use the leg colour characters in this couplet and leave out the antennal character because otherwise, it will create difficulties re-routing the key.
couplet 6 – the ‘Only first segment of antennae black’ option leads to couplet 7 which is fulvicornis and latifrons. It needs to lead to couplet 8! (and conversely, the other option needs to go to couplet 7)
couplet 7 – the reference to ‘more sparingly punctured’ in latifrons is hard to appreciate. However, I agree that it is definitely less strongly punctured, with reticulate interstices. To say it is dull is potentially misleading if the specimen is identified in isolation. It is relatively more dull than fulvicornis.
couplet 8 – the ridge like interstice character for separating oscillator and tarsalis is really easy to see – great feature! I would also agree that the punctation is appreciably less strong in oscillator – again a really easy feature to appreciate, but I think both of these characteristics are only appreciated when you have both species to compare. Useful though………
Stenus fulvicornis species description:
second line ‘slightly weaker punctation’ should read ‘slightly stronger punctation’.
Stenus latifrons species description:
typo – ‘Often seen with the plant climbering species…………’
Stenus solutus species description:
typo – ‘Differs from cicindeloides in the not very shing upper surface’.
Stenus tarsalis species description:
typo – ‘Male have distinct emarginations………’ should read Males
Hypostenus key species descriptions:
typo under Stenus latifrons line 3 ‘longer than the fourth and not nopticeably narrowed apically.’
typo under Stenus oscillator line 5 ‘unlike tarsalis where there are obvious.’
Steninae key:
page 2 – in the description under Dianous coerulescens line 4 states that the temples are ‘nearly as long as the eyes’ yet in both the key and the general description for the genus Dianous it is stated that the temples are ‘greater than the diameter of the eye’ and ‘longer than the width of the eye’.
The aedeagi of my dozen or so ossium specimens all bear a close resemblance to that figured for palustris on page 16 – have I misidentified my specimens?
Page 8 – couplet 5, glacialis option line 2 reads ‘legs yellow with middle but hind femora broadly black at apex’ – this doesn’t make sense
page 9 – typo line 3 – ‘….and on the termial’
Species descriptions:
Stenus aceris line 3 should reference Fig 6 not 11 and line 5 should reference Fig 8 not 13.
Stenus impressus line 5 should reference Fig. 7 not 12
Stenus ludyi line 5 should reference Fig. 9 not 14
typo – under Stenus ossium line 4 ‘In moss an tussocks……..’
typo – under Stenus subaeneus line 3 should read ‘tibiae’ not ‘tibia’
Page 15 – Aedeagus diagrams
ochropus and ludyi are mixed up; the diagram of the aedeagus of ochropus is in fact that of ludyi and visa versa.
It should be noted that all of my comments refer to the original test version for these keys, and not the revised ones. The revised key has taken into account all of my comments in the first 2 sets of comments from March 27th.
The page and line numbers that I’ve referred to in all sets of corrections, will not easily reference to those in the newer versions of the test keys.
Metatesnus key:
Excellent key – just three comments:
typo in couplet 2 ‘club brwon to black’
I always notice the small unpunctured area in the centre of the pronotum of flavipes as a diagnostic feature of that species – this might be worth including in the species description.
and finally, Stenus butrintensis is also recorded from the Midlands – dissected males from Warwickshire – Ryton Wood pool in 1988 (SALane) and Bubbenhall Bridge in 1997 (DJMann).
Roy, Hemistenus:
I think the ‘palustris’ aedeagus illustrated on last page of test key version 2 is ossium.
I think your ‘ossium’ aedeagus illustration in version 1 (which you subsituted in v2) was actually palustris.
HYPOSTENUS.
Couplet 4…..fairly dull black…..similis.
Description 7…similis. moderately shining surface…
Couplet 3 second part. ,first and second antennal segments brown to black…6
Description 9 …tarsalis. …possessing a single dark basal segment…..
On tarsalis. I have a specimen that has apex of antennae and palps dark to fuscous.
Couplet 6 second part. First two segments of antennae black….
Description 6..oscillator. …one dark basal segment….
On impressus. I have specimens with the first antennal segs. dark to fuscous and one with apical palps darkened.
The above can be ignored if both avenues of a couplet are followed. Well done Roy. It’s great to have the beasts under one roof.
On the distribution of Stenus guynemeri, it states West Wales.
Last year I found it at two localites near Llangollen in North East wales. I suspect it is abundant on fast flowing streams in Nort East Wales
Bryan Formstone
In the key to Stenus s. str. couplet 13 starts with length: 3-4mm or 5-6.5mm. Well, I’ve just looked at a specimen of Stenus providus which is 4.25mm long, as per Joy, and thus couldn’t be reached in the test key where one has to say 5-6.5mm to reach this species. Stenus clavicornis and Stenus lustrator, both also reached via the 5-6.5mm question, are both slightly larger (according to Joy), but still not within the 5-6.5mm range. Perhaps, it should be 4-5.5mm rather 5-6.5mm?
Stenus flavipes, basal antennal segment described as black, but I would say ‘darkened’ – it certainly isn’t black as in similis. I only have 2 specimens to look at though.