Insect monitoring traps

Monitoring traps are the highest return on investment in preventive conservation. They cost very little, they require no expertise to deploy, and they detect a category of damage that is fast, irreversible and otherwise invisible until it is severe.

Their value, however, comes almost entirely from the discipline around them rather than from the traps themselves.

Where to put them

Crawling insects follow edges. A trap in the middle of a floor catches a fraction of what the same trap catches against a skirting board.

• Along walls and in corners, particularly in stores.
• Under and behind furniture, shelving and plinths.
• Near external doors, service ducts, pipe penetrations and anywhere a bird could nest above.
• Inside stores holding textiles, fur, feather, skin, herbaria and taxidermy, which are the material at real risk.
• In the loading bay and the quarantine area, which is where problems arrive.
• In areas where food is consumed, which in most buildings is more places than officially permitted.

Number every trap and mark its position on a plan. Unnumbered traps produce a count with no location, which is very nearly useless because the whole point is to find out where.

Checking and recording

Monthly is the working standard. Quarterly still detects a problem eventually, but loses the seasonal pattern that distinguishes an indoor breeding population from insects wandering in from outside.

At each check, record for every trap: the date, the number of each species or group found, and whether the trap was replaced. Record zero explicitly. A blank space in a register is ambiguous forever, whereas a recorded zero is data.

Traps should be replaced when the adhesive dulls or when they are full, and in any case at least annually. A trap that has been down for three years is not measuring the last month.

Reading the results

A single count means very little. The value is in the series.

A rising count in one location points to a source in that location. Look above, below and behind: a nest in a void, a dead bird, a forgotten box of wool.

A seasonal peak with nothing between suggests adults flying in from outside during their flight season. The response is exclusion, not treatment.

A steady count all year suggests a breeding population indoors, which is the more serious finding.

Silverfish and booklice rising is often a humidity signal before it is a pest finding. Both need damp to persist. Put a logger in that space before ordering any treatment.

Scavengers such as spider beetles point at accumulated debris, dead insects and general housekeeping rather than at the collection itself.

Identification is the other half

A count is not interpretable without knowing what was caught, because the species determines whether you have a collection problem, a building problem or a housekeeping problem. Identifying museum pests covers the main groups.

Keep the specimens. A photograph through a hand lens or a phone macro attachment, filed with the count, allows a later reviewer to check an identification that turned out to matter. When a count is high and the identification is uncertain, that is the moment to ask someone who knows rather than to guess.

What follows a positive finding

Isolate first. The affected material goes into sealed bags or boxes before it is moved anywhere, so that a store-level problem does not become a building-level one.

Then treat, by freezing or anoxia depending on the material. Then find and remove the source, which is the step most often skipped and the reason infestations recur. Then keep watching the traps in that area at a shorter interval until the counts return to baseline.