Tuesday, 12 January 2021

South Wales Bristletails - Order Microcoryphia

Some pointers if your looking to get Bristletails - Order Microcoryphia identified from photos.

We currently have six species in south Wales...Dilta chateri, D. hibernica, D. littoralis, Petrobius maritimus, P. brevistylis and Trigoniophthalmus alternatus. 
 
Note: Dilta saxicola could also turn up here? For now at least, it seems to be restricted to Ireland (?)... Delaney (1954) has it as 'Howth Head, Dublin'. I've no idea what this species looks like and can't seem to find much info on it in general. Would appreciate any photos, info etc.
 
Two important positions to capture when taking photos...
 
1. A top down pic (or close enough) of whole animal; body pattern is important for separating some species - especially Dilta. Trigoniophthalmus alternatus will also have a notable body pattern, useful if unable to get a look at ocelli position. Petrobius not so much, as both can be very similar looking - head on shot important for these.
 
2. A close as possible photo of face; position of ocelli below compound eyes - important for separating to Genus (until experience is gained). Also, a good view of 'shading' on the face of Petrobius will be key in splitting the two in the field.

Note: You will often find Dilta without scales (pic below). You will then need to check for a male (always worth taking a voucher specimen, just in case..could also find something new?) or you could try rearing it until it has gone through a moult or two? They are also a reddish pink when really young.
 
Dilta chateri without scales
 
Useful links to keys...
Check out Order Microcoryphia (PDF)
Delaney key..topmost PDF Vol 1Part 2

 

Dilta spp...Short antennae; ocelli under outer corners of compound eye

Dilta hibernica
Dilta hibernica showing ocelli position under compound eye
 

Dilta chateri. A common species in south Wales. Was found new to science by Arthur Chater in 1995 after he undertook a survey of the Thysanura in Cardiganshire. At that time he assumed that the commonest species there was D. hibernica, it was only after he published the survey in the Dyfed Invertebrate Group Newsletter that he realised it was something different. (He has since commented that he's never found true D. hibernica in Cardiganshire). https://yrefail.net/dig/DIG_Vol22.pdf

D. chateri is currently only known from Wales, though probably overlooked elsewhere due to it often being mistaken for D. hibernica?  I've seen possible photo evidence of D. chateri around Bath, Bristol and Cornwall areas. Be great to get one confirmed.

Dilta chateri showing the dark band to rear of the hump

The above specimen is in what i call 'full splendor' and showing the dark band to rear of the hump - diagnostic. It won't always be this thick (often with a thin band) and will occasionally be broken in the middle. T. alternatus will also have a similar band. 

Dilta chateri
Side on view of fresh moult D. chateri
Dilta chateri
D. chateri showing thin dark band to rear of hump and typical body pattern


Dilta hibernica. Not so common in south Wales, i don't find it too often in the Valleys. When i do come across it, it tends to be in wooded limestone areas. Hard Fern - Blechnum spicant overhanging path banks, rock ledges etc are a good a place as any to collect these, along with other Bristletails.

Dilta hibernica
Dilta hibernica in full splendor (photo by Chris Lawrence..one of my specimens)

If you look close at photo above, you will see a dark V shape band running back from front center of hump down along body sides. There will also be a pale circular patch on body, found just above the pale area at base of tails - looking to be diagnostic?   

Note: a similar pale area can occasionally be seen in some fresh moult D. chateri.

Dilta hibernica
Dark Dilta hibernica showing pale area part way up from tails.

Ive used this bad pic of a D. hibernica to illustrate how clear the pale circular area can usually be seen. This and the dark V over hump diagnostic in separating it from the other two Dilta spp.


Dilta littoralis. Looks to be scarce in south Wales, known from an handful of sites. It occurs mainly on coastal sites and on heaths, grasslands, scree slopes etc. Though, it has been found on heath and a colliery site in the Shirowy Valley (the one below), some 20miles inland from the coast.

Dilta littoralis
Dilta littoralis with dark broken lines running length of body.

These don't seem to be as showy as the other two, often seen with dark broken lines running length of body, as shown in photo below.

Full splendor specimens will show light brown between these lines. Image of one hear...
https://www.facebook.com/groups/438740999565613/permalink/3110060712433615/

Dilta littoralis
Dilta littoralis

Note: Dilta littoralis specimens that have lost their scales are possibly black and not cream-pinkish when 'bald' as in D. chateri and possibly D. hibernica? Needs more checking.

 

Petrobius spp...Antennae longer than body, ocelli 'hour glass' shaped under compound eyes.

Petrobius brevistylis. A common species considered to be confined to the coast. It likes to occupy sites with access to large continuous rocky surfaces immediately above the high tide mark. Regularly found in same areas where you would find Sea-slaters - Ligia oceanica.

Petrobius
Petrobius showing long antennae

Not possible to separate P. brevistylis from P. maritimus on body pattern. A close look at the face is needed to check for scales or lack of.

Petrobius brevistylis
Petrobius brevistylis. Scales clearly visible face; face looks darker (Photo by Matt Prince).

A look at the face head on, you will see dark scales on the frons; area by outer corner of compound eye etc; (see Mick's Microcoryphia key in above link for better understanding or where to look) head looking generally darker in appearance.


Petrobius maritimus. A common coastal species that can also be found inland, have been known to enter homes. In areas where these two species occur together, a considerable degree of habitat separation can often be noticed. P. brevistylis will occupy sites with large areas of rocky surfaces, while P. maritimus usually occupies the upper surfaces of smaller stones. The average population density is greater in P. brevistylis than in P. maritimus. P. brevistylis is considered the more successful of the two species in Britain (Davies and Richardson, 1970).

Petrobius maritimus
Petrobius maritimus

Petrobius maritimus. Head generally paler with darker areas absent from frons and area by outer corner of compound eyes etc (see Mick's Microcoryphia key in above link for better understanding or where to look). A black marking is present on the pleural fold.

 

Trigoniophthalmus...Antennae same length as body; ocelli beneath middle of compound eyes.

Trigoniophthalmus alternatus...a scarce species in south Wales and the rest of Britain for that matter. This one often turns up in gardens and will venture into homes. 

Trigoniophthalmus alternatus from a garden wall in Tongwynlais

Pale hump with dark band over rear. Overall body pattern seems consistent in this species? Some side on shots can have an appearance of Dilta chateri. Though, if you manage to get a look at the ocelli position, then it will be unmistakable..especially if you have a worn specimen. 


Extra info, images, habitat photos and species info below. Any confirmed images, extra info etc would be most welcome. Will keep updating this post as going along. 

 

Dilta chateri
An overwintered Dilta chateri showing a bronze colour

 

 

Dilta chateri and D. hibernica habitat
Dilta chateri and D. hibernica habitat

 

Dilta hibernica...Sarah Patton
Dilta hibernica (image by Sarah Patton)

  

 

Dilta chateri and D. hibernica habitat
Dilta chateri and D. hibernica habitat


Dilta hibernica
Dilta hibernica


Petrobius maritimus habitat
Petrobius maritimus habitat





































































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