I occasionally still get asked to predict the date when the first Glow Worm will appear at Clipstone Old Quarter each year? It's a difficult question to answer with any degree of accuracy, although people expect it to be easy after monitoring this famous Glow Worm colony for well over a decade. Such predictions are difficult and will always be largely guesswork at best, as there are a number of factors needed to be taken into account and they vary from year to year. Temperature over preceding months, or over the previous year is certainly one and unsympathetic habitat management, or the success of larvae finding food are others.

Periods of prolonged snow, ice or heavy rain, drought and high temperatures are other factors which can affect larval and pupal development. The hot, dry summer of 2022 may well prove to have had serious implications on many Glow Worm populations across much of the UK and so counts at some sites affected by the dry conditions may well be down on recent years. In Nottinghamshire, those Glow Worm colonies situated on areas of heathland will likely be the most affected, although this remains to be seen.

The Sherwood Forest area has undergone periods of very dry conditions in previous years, which, if they continued for any length of time, were showed through observations to lead to the dehydration of a large number of larvae. During larval surveying in the late Summer and early Autumn of 2013 (another very dry Summer) Dilys and I found some larvae were becoming paper thin through dehydration and when rain eventually arrived on September 6th, we recorded larvae taking on much needed water. The summer of 2022 though, was on another level in comparison to what I have personally witnessed at Sherwood Forest previously.

The variabilities of the UK weather is without doubt the biggest factor in determining when any species will appear, but it's not just the weather or conditions around the time of adult emergence, but over the course of the previous few months and probably well over the past year that needs to be borne in mind.

For larvae going on to become adult this Spring and Summer, it is necessary for those larvae to have had suitable conditions for hunting and to have managed to find enough food over the previous Summer and Autumn and that is probably be more critical than the immediate Spring period. We always thought that most pre-pupation development took place place prior to over-wintering and in captivity, we certainly had over-wintering larvae never eat anything before pupation.