Saturday, 17 March 2018

Choice of pinning system - direct pinning or staged mounts?

Not all insects can be identified in the field or from photographs; indeed, the majority probably cannot. There are, however, a few specialists who can do a fair bit in the field and from photographs. They can only do so because they have spent many years studying preserved specimens. Most observers of the natural world probably will not want to delve that deeply into species identification, but they may be keen to get specialists to do the identification for them. So, we definitely need specialists who have taken the trouble to develop the requisite skills. Newcomers will only manage this by taking specimens and making the necessary microscopic studies to hone their skills. Some advice on how to prepare and preserve specimens is therefore a necessary part of the mentoring process.

So, you have decided that you need to retain specimens in order to develop your technical skills. How do you set about it? For this session I will concentrate on the choice of pins for specimens that have been killed using your chosen medium (freezing, ethyl acetate, crushed laurel leaves).

Let us start with the critical issue. The ‘collection’ is not there to be an adornment – it is a working tool and the specimens need to be prepared so that they can be examined carefully from all angles. Equally importantly, the specimen is of no real value unless it is accompanied by relevant data – who collected it, the date on which it was taken, the locality name and a grid reference (in the UK using standard OS grid is probably best recognised). So, the specimen needs to have at least one, and possibly several labels. Once you have put an identity to it you will need at least a second label. So you need space on the pin.

For most Hymenoptera and flies, there are two main ways of pinning. Traditionally, a long pin has been used directly through the specimen. There are two lengths of pin that have been used – ‘English’ pins that are 30mm long, and ‘Continental’ pins that are 38mm long. Museums tend to favour Continental length pins because they have more space on which to place labels. However, many ‘collectors’ of old would use ‘English’ pins because they take up less space, require shallower boxes and are cheaper (standard lacemaking pins). I much prefer the longer continental pins because they also allow a lot more space for handling specimens without damaging the specimen.

Directly pinning using Continental pins carries with it the problem of storing lots of specimens whilst they dry and before they are fully labelled, but it does mean that you only have to write your data labels and place these on the pin. Many (but not all) Hymenopterists use this system.

There is the alternative that many Dipterists favour: short ‘micro’ pins made of stainless steel and produced in a variety of lengths and thicknesses from AA (the finest and most expensive) to E. For the most part pins graded A1 to A3, B1 to B3 and C1 to C3 are likely to suffice for the vast majority of Hymenoptera and Diptera in northern Europe. I tend to use a mixture of A1, B1 and B2 for all of my work (I never need to pin the larger animals as these are often doable in the field or I don't attempt them (e.g. bumblebees - if I cannot do it in the field I would not take a specimen - so I don't record many bumblebees).

If you work with micro-pins you have the advantage that you can store large numbers of specimens in a relatively confined space. Dipterists tend to use ‘Crystal Boxes’ – clear plastic boxes with a plastozote lining. These boxes are relatively pest-proof, can easily be stored and are a good way to keep specimens before staging and labelling (see Figure 1).
Figure 1. Micro-pinned specimens in cyrystal box. These include occasional beetles too, although pinning is probably not the way any serious Coleopterist would work! (I simply find it convenient)
The problem with micro-pins is that you then need to create a stage for the specimen on a longer pin (ideally a continental length pin). This is a fiddly and time-consuming job! But, staging does bring the advantage that the ‘stage’ acts as a bit of a shock-absorber (Figure 2). There are no conventions to the size of stage that you should use, nor to label size, but it is worth bearing in mind that the bigger the label and stage, the more space that will be required to store specimens – and that can get expensive! The other thing to bear in mind is that you will probably want to investigate both the upper and lower sides of your specimen, so big wide stages may impede your view of critical features; which is why I opt for narrow 3mm x 3mm stages of about 1.5cm long.
Figure 2. Staged and labelled Sciomyzidae - note two types of Continental pins used here - the expensive ones with nylon heads and the cheaper steel-headed pins bought because devaluation of the Pound has pushed the Austerlitz pins out of my price range!
The next and most important question is how to prepare labels? If you have nice neat hand writing you can of course do so using a permanent marker pen or Rotring pen. My eyesight and hand writing are too poor for this and I don’t have the time to write vast numbers of labels; so I generate them on the computer and print them onto thin card (ideally acid-free). Don’t use ink-jet printer unless you get permanent museum-grade ink. Other inks will fade and become illegible. A laser-printer is far more reliable and produces cleaner labels. I tend to go for labels in 6 point and using 0.7-line spaces. In so doing I can usually create labels approximately 1.5 cm by 1 cm. Remember that the labels need to be legible (at least under magnification) and they need to last if the specimen is to be of any long-term use.

Finally, it is important to remember that a 'collection' need not be a work of art! I tend te refer to specimens as 'a bit of chitin on a pin'. The real value of the collection is the science, so the specimens need to be accessible but not beautiful. I tend to side-pin pretty nearly everything with flies and have now started to side-pin some aculeates too (e.g. Pompilidae). Carefully spreading the wings may have no real value but may be aesthetically pleasing. But, it is important to be able to see relevant venation, so making sure critical features are exposed is essential. This can mean teasing out male genital capsules, ovipositors and possibly opening mouthparts (some bees). It is fiddly and time-consuming, and you often need to hold these structures in place whilst the specimen dries out - that is a definite advantage to micro-pinning!


  1. If cutting plastazote staging strips is too time consuming or fiddly, you can buy them from the usual suppliers. Unlike the ones shown they're a finer grade foam that grips the pin more securely. Maloclm Storey

    1. Not true Malcolm. The bought foam is far coarser and is absolutely no better in terms of grip, but is a lot more expensive! The only real difference is that it is slightly less pliable.

  2. Well put as ever Roger, feature accessibility over nice looking posture. my experience of field pinning of hymenoptera taught me to check the feet are not hooked into the p'zote before removing for staging.

  3. Your/my clock but not on my pc is out I sent the above at 13:34 not 06:34 as shown, I wonder what you were doing up a 03:32?

    1. Sound asleep I'm afraid Mark. I completed this about 23.30 on 17th!