Preserving butterfly specimens for a home collection

Why butterfly specimens deteriorate

A pinned butterfly can last for centuries, but only if the conditions around it are right. The enemies are predictable: damp, light, pests, and clumsy fingers. Our British climate is kind to living butterflies and unkind to dead ones, because average indoor humidity often sits above the level at which delicate wing scales begin to lift and mould spores find a foothold.

The scales that give a Red Admiral its colour are pigments and microscopic structures resting loosely on a membrane. Rub them once and the colour is gone for good, which is why collectors speak of specimens being "rubbed" as a serious defect. Add to that the fact that most insect collections are eaten not by moths but by the larvae of dermestid beetles, and you have three clear jobs: control the moisture, control the pests, and handle everything as though it were made of ash.

Setting up storage that actually seals

Purpose-built entomological cabinets are the gold standard, with tightly fitting drawers and a gasket or rebate that keeps out dust and wandering insects. For a home collection, a good-quality plastic box with a rubber gasket seal does the same job at a fraction of the cost.

• Line the base with cork sheet or closed-cell foam about 6mm thick, so pins sit firmly and can be pushed in without bending.
• Pin a label inside the lid naming the box and its contents, so a misplaced drawer can be reunited with its owner.
• Keep boxes on a stable shelf, away from radiators, windows, and the damp of an outside wall.
• Avoid lofts, garages, cellars and conservatories. All four swing wildly in temperature and humidity across a British year.

A cool, dark room with steady conditions beats a warm display case every time. If you want to show specimens off, rotate a small selection and keep the bulk in storage.

Holding humidity steady

Aim for a relative humidity between 45 and 50 per cent, and check it with a small digital hygrometer kept inside the storage box or cabinet. Below about 40 per cent, wings become brittle and abdomens shrink; above 60 per cent, mould and "grease" become a real risk.

• Use silica gel in a breathable sachet or perforated container, never loose where it can abrade specimens.
• Recharge the gel every three to six months by drying it in a low oven until it turns back to its indicator colour.
• Avoid sealed boxes with no buffer at all. A little conditioned silica is better than none, and better than far too much.
• Open boxes briefly on dry, still days for a gentle airing, then close them again before the evening damp arrives.

If you notice wings curling upwards or abdomens drooping, that is usually a sign of damp. If pins begin to corrode, it is almost always humidity plus residual salts from handling.

Defending against pests

Check every drawer monthly for the tell-tale signs: fine grey dust beneath a specimen, a hollow thorax, or tiny cast skins near the pin. Museum beetles, booklice and clothes moths all find dried insect tissue irresistible.

• Quarantine all new material. Keep incoming specimens in a separate sealed box for at least a month before they join the main collection.
• Freeze suspect items. Double-bag them, freeze at around -20°C for 72 hours, then let them return to room temperature slowly before opening the bags.
• Use a proprietary pest strip designed for insect collections, placed in a perforated container so it never touches specimens. Replace it at the interval stated on the label.
• Keep the storage area clean. Vacuum shelves and corners, and never store wool, dried plant material or forgotten sandwiches nearby.

Chemical control is a supplement, not a substitute. Airtight storage and vigilance do most of the work.

Mounting so the wings survive

Fresh specimens should be set within a day or two of death; dried ones need relaxing first in a sealed container over damp sand or blotting paper for 12 to 48 hours until the wings move freely.

• Pin through the thorax, slightly to the right of the midline, so the pin never obscures the centre of the insect.
• Draw the wings forward with a fine needle and hold them flat with paper strips pinned just outside the wing margins.
• Leave specimens on the setting board in a dry, airy, dust-free spot for two to three weeks before transferring them to storage.
• Never grip a specimen by the wings. Lift it by the pin, or slide a card beneath it.

Labels, records and long-term care

A specimen without data is decoration; with data it is evidence. Pin a small label beneath each butterfly giving the locality with a grid reference, the date, the collector's name, and how it was caught or reared. Use acid-free card and pencil or archival ink, which survive damp and time far better than ballpoint.

Once a year, go through the collection properly. Top up silica gel, swap pest strips, check for verdigris on old pins, and re-pin anything that has worked loose. Keep a simple written index of what lives in each box. Handled this way, your specimens will still be fit for study long after the nettle patch where they were caught has been built over.