… a guest blog by Radoslav Valkov, member of the Flemish Entomological Society and the editorial team of their journal, Phegea. Radoslav presents his reflections on the importance of habitat preservation and draws our attention to rare species, using his old and ecologically valuable garden in Bulgaria as a survey site for the Horehound Long-horn Moth (Nemophora fasciella).
I have previously mentioned on Buglife’s blog that the role of common plants remains neglected, such as the plant Black Horehound (Ballota nigra). This July, I conducted a survey that focused exclusively on the Horehound Long-horn Moth at a population level. The results reaffirmed my belief that preserving the natural habitat at home is always rewarded. It served an excellent means of empirical validation of the delicate nature of this species. Having a micro-moth within a small habitat was a convenient spatial constraint that greatly facilitated the study.
The Horehound Long-horn Moth is a beautiful species. In addition, it is an example of an insect that irregularly establishes small populations. They are hard to monitor and the moth, quite possibly, remains under recorded and overlooked in terms of its ecological significance. This is among the most elusive micro-moth species in the UK and Europe, and one would say it is impossible to sample a population; records are scattered and are often one-off observations. Thus, I was determined to find out more about the population and its inexplicably transient presence.
The survey commenced on the 4th July, and the last individual observed put the research to an end on the 20th July. I had to chase up the tiny micro-moth during the hottest hours, exposed to 43.5°C. The Horehound Long-horn Moth actually enjoys heat and sunshine. The sampling process started with the observation of a male individual feeding on the nectar of Common Mint (Mentha spicata). Initially, both females and males were found to occupy an area that is a dense plant shelter of Common Hop (Humulus lupulus). This was undoubtedly odd because a specialist, whose larvae feed exclusively on Black Horehound, would be reasonably expected to be confined within the narrow larval food plant area. To improve chances of finding a mate mating and laying eggs, and to reduce energy expenditure, many short-lived insects can be found near the larval food plant. However, this assumption cannot be a used as a reliable frame of reference to predict limited dispersal range. The mobility of adult Horehound Long-horn Moths requires further investigation.
Gradually, the moths switched to an area with growing Black Horehound. The population became more compact, making use of Japanese Rose (Kerria japonica) as a shelter when at rest. Male moths travel much longer distances, in contrast to the females that retain the preferred patch, where they were found to lay eggs. After the small population relocated, their newly preferred patch started receiving frequent irrigation. This had a largely positive effect on retaining their area.
Locating individuals was a significant challenge because I had to gently inspect the area by means of disturbance, e.g. touching and moving stems and branches very carefully. The fact that it was not always possible to find a moth conspicuously positioned on a leaf did not mean there were not individuals to see. In the case of light disturbance of the vegetation, this caused two types of behaviour: 1) leaving the patch and seeking shelter; 2) take-off and landing within the same area, followed by a short period of rest and then continuous oviposition. Males are much more agile and tend to occupy treetops; they have been previously reported to rest on the bottom side of the leaves of other dense thorny shrubs, like Blackthorn (Prunus spinosa).
It becomes clear that the overwhelmingly inconspicuous lifestyle of this micro-moth can be ascribed to its clever strategy to remain among vegetation, quite often entering inaccessible and densely branched spaces where the insect is less vulnerable to predation by birds. This is why finding the moth required a thorough investigation and readiness to spend many hours of careful repeated scans within a small perimeter. The flight of the female is a short-distance one; discerning where the moth had landed following a short travel was a challenge due to the possibility to confuse the moth with other delicate micromoths. During an observation, I thought it was a Horehound Long-horn Moth disturbed and it turned out Cream-spot Bark Moth (Dasycera oliviella).
What I considered a striking behavioural pattern, was the fact that after continued disturbance in the perimeter, a female individual always starts performing oviposition, making use of a single plant stem for more than 10 minutes. It is not known if prior to the moment of disturbance and take-off an individual was actually performing oviposition or at rest. Either way, continued disturbance resulted in intense oviposition, which is an incredible example of an active response to quickly aid reproduction. This behaviour was noticeably amplified by the increased irrigation of the Black Horehound plants.
The study returned 27 individual records, and it would appear that watering the plants helped the moths to cope with the heatwave. And as extreme weather events, such as severe summer droughts and high temperatures, become more common this is likely to impact upon many species of invertebrates, including rare micro-moths. Horehound Long-horn Moth is a thermophilous diurnal moth that is typically active in sunny warm conditions. However, the lack of adequate rainfall actually forced the population to retreat to the cooler shrubby areas of the garden. Also, the foodplant, Black Horehound, was abnormally absent this year, as opposed to previous years. Normally, there is a regular succession of Red Deadnettle (Lamium purpureum), and later Black Horehound. In 2024, such a sequence just did not take place. Nevertheless, they appear to have been able to adapt – to a point.
The subtle underlying factors that determine the irregular population count, seasonality of the occurrences and the detailed ecology of this species are yet to be explored further. What I personally find exceptionally interesting, is the opportunity to monitor this understudied species at home. The more I attempt to learn about it, the greater the number of questions I have. Their answers inevitably require repeating this survey and I look forward to doing it with more precision, with much more detailed ethological profiling and collecting even more valuable information at a population level. Some uplifting news is that the diversity of Fairy Moths (family Adelidae) in the garden is increasing; on 29 April 2023 another interesting moth was observed – Green Long-horn Moth (Adela reaumurella).
As a final remark, it can be inferred that watering my garden this summer has helped this moth species to cope with the high temperatures and drought. But this cannot be done across the countryside so we need to think of other solutions – which will come with a better understanding of the species’ ecology.
Radolav has an active GoFundMe campaign to raise funds for equipment to allow him to improve his surveys. You can read more about it and see some of Radoslav’s amazing macro-photography here.
