Over 20,000 Moths in one night!!

Dave Grundy – leading authority on Andalusian moths and expert guide for Inglorious Bustards’ Mothing The Straits holiday – tells us about this phenomenal eruption of Gypsy Moths!

So, what’s the most moths you’ve ever had in your moth trap? And what’s the most of one species? I’ve heard talk of 750 Large Yellow Underwings (Noctua pronuba) in one trap in the UK and maybe as many as 2,000 total moths in the trap of all species?

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Gypsy Moth trap bedlam!! © Dave Grundy

Well this month I have had an interesting time with numbers of moths of one species in particular – the Gypsy Moth (Lymantria dispar). It causes economic damage to forestry in North America – where it was introduced – and also on a local level in Europe.

There has been a population explosion in The Straits of Gibraltar area of Andalucía, from Algeciras to Tarifa along the coast and up to about 8 kilometres inland. Beyond that, the species is flying but does not appear to be in any large numbers (we saw only 36 across 6 traps near San Roque on 27th June).

I was first aware of the larvae back on 17th May 2020 when I recorded at least 10 in my notebook when trapping at Huerta Grande, Pelayo, Andalucía, with José Manuel Gaona Ríos.  We then went to Bosque de Niebla trapping on 5th June 2020 with Rafael Rodriguez Pino when my notebook just says “millions of caterpillars stripping the oak trees of all leaves”. This must have a massive effect on the ecology of other insect species dependent on the leaves and also on bird life and others dependent on the trees and insects.  

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Gypsy Moth larvae © Dave Grundy

But is this a phenomenon to be celebrated as a marvel of nature or to be horrified about?  Could climate change be a factor? This event, which occurs cyclically every few years, is now occurring more and more often, coinciding with periods of drought.  I don’t know what the answer is. However, I am definitely not a fan of attempts to eradicate on a large scale as this causes damage to so much other wildlife at the same time.

Next I saw my first ever male Gypsy Moth in Spain on 6th June 2020 – what a stunning creature when fresh and new! This was at Centro Internacional de Migración de Aves (CIMA), Tarifa, where we do not have the oak tree foodplants for the larvae to feed on, but they disperse here looking for females, which struggle to fly far from their original location. 

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male Gypsy Moth © Dave Grundy

Numbers then began to increase with 325 recorded on 15th June 2020 and 673 on 17th June and then a stunning estimated 5,000 to one trap on 19th June in calmer weather – this was ridiculous! An estimated 4,940 came to one trap on 20th June and then numbers have been up and down since, with more on calm nights and less on windy nights.

My peak count was on 28th June 2020 when I estimated 24,850 between 5 traps and 10,900 in just one of those traps! Moth recording becomes a nightmare and I even had to wear my COVID mask because of all the scales in the air! I believe and hope we are now near the peak in numbers, so I can return to normal moth-trapping soon! 

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There seems to be a few Gypsy Moths in this trap! © Dave Grundy

But yet, how spectacular! At nearby sights just north of Tarifa I have recorded over 5,000 at La Peña and over 1800 at Punta Paloma. And to put the numbers into perspective I have now recorded since February in Spain a total of over 650 species and over 106,000 moths, but of those 60,690 have been of Gypsy Moth adult males since 6th June 2020! 

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Records of Gypsy Moths at CIMA © Dave Grundy

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