Saturday, 21 January 2023

Moth Detective

 I first noticed the magic of butterflies when I was about 10 years old. My neighbour's garden, back then, was full of Michaelmas Daisy borders and in late summer I was mesmerised by the sight of dozens of Red Admirals, Small Tortoiseshells, Peacocks and the occasional Comma, feasting on the flower heads.

My interest in moths started at the same time. My mother would regularly wake me up from bed in the late evening to see if I could identify the moths flying around the garage light.

Ever since then, my interest in both groups has run side-by-side.

Nowadays, I occasionally come across something that I can't pin down to species level. It is most often the early stage of a moth species, particularly ovum or pupa, that requires a bit of research and detective work.

Here are a couple of examples.

Gold Spot (Plusia festucae)

Back in August 2017, I came across a moth pupa hanging by its cremaster from a ruptured cocoon in a ditch side reed bed on Pevensey Levels. The pupa was black and green and had probably been disturbed by cattle that regularly walk through the reeds to drink from the ditch. I had seen these cocoons before but had rather assumed that they were some sort spider egg cocoon. 

Black and green may have been its normal colour but it may also have only recently pupated and not yet attained a more usual all black livery. I don't generally like to bring things home from the wild but there seemed little chance of it surviving the winter and there was a chance I could see what emerged in the spring. Sadly the pupa did not survive. The plan now was to find a larva during the following season.

In September 2019, I came across a mature larva feeding in the same reed bed. I took photographs and when I got home, managed to identify it as a Gold Spot (P. festucae). Note just two pairs of prolegs.

On checking my books, it was clear that Gold Spot fitted the bill but I wanted to see the larva through to pupation to be sure. I returned the very next day to find that the larva had constructed its cocoon. The larva is clearly visible inside the cocoon.

A few days later and a black pupa is just visible in the cocoon.

An adult moth.
 Although I occasionally get them to my moth-trap in my garden, I didn't realise quite how at home festucae is in damp habitats.

Scarce Umber (Agriopis aurantiaria)

In December 2018, I was in a local Wealden wood, searching through oak branches for Purple Hairstreak (Favonius quercus) ova. I had found a couple but then came across an odd looking ovum which rather stumped me. I got it stuck in my head that it might be a deformed quercus ovum. It had been laid at the base of an oak bud, exactly where a Purple Hairstreak would have laid her egg.

After a day or two, I steered myself away from the deformed egg theory and decided to research what moths overwinter in the egg stage and lay on oak. Starting with the Geometrids, I eventually homed in on a prime candidate. The Scarce Umber (A.aurantiaria) is on the wing during late autumn and early winter and the flightless females indeed lay their eggs on oak (and other broadleaf trees). 

In April 2019, I returned to inspect the same oak branch that I found the egg on and saw this early instar aurantiaria larva on the opening oak buds.

Another larva on honeysuckle, shedding its skin, in April 2017.

An adult male Scarce Umber.

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