Saturday, 31 August 2019

Lost moths

I would be grateful for any thoughts on my "Lost moths".

I have noticed, recently, the number of moths in my trap reducing and, for a couple of nights there have been none at all. I have the sort of trap that has two perspex sheets angled down into a box to let the moths in easily but make it difficult for them to get out.

I know moths are entering the box, albeit perhaps in reduced numbers. For example last night I had a look about 11:30 and there were several moths in the trap including a number of Thorns and large yellow underwings, but the trap was completely empty this morning.

The perspex sheets seemed to be a bit "Cloudy", so I gave them a clean but, on closer inspection, the sheets were slightly scored giving the cloudy appearance.  I wonder if this gave moths a purchase to escape but find it hard to believe all moths would get out this way and, in any case, how did this scoring occur? I have checked carefully and there are no gaps in the box construction that would allow all bar the smallest moths to get out.

There have been bats patrolling the area for as long as I can remember and, certainly, since I have been attracting moths with my trap, they will "hawk" and take flying moths, but I can't imagine them getting in and out of the trap and taking moths. If by some chance they did, there would be evidence, the occasional bat unable to escape again, bat droppings, moth wings etc.

I would be grateful for any thoughts on this problem. Perhaps just buy a different trap design!!

Photo of trap taken at 21:45 below following helpful advice from Dave and Nigel. (Thorn can be seen on inside edge; will it be there in the morning).

Alan Diver


  1. Hello Alan,

    Could you perhaps take a picture of your trap and add it in to your report? I presume it is a basic Skinner design but it would be helpful to see what sort of light you use with it, etc. Click on the yellow pencil symbol at the bottom of your post and it'll take you back to the composition page.

  2. Hi Alan, I'm assuming, from what you've said, that you leave checking the moths in the trap until morning. Do you do this before it gets light? If not then I suspect various bird/rodent species have learnt where there's an early morning feast to be had. Any signs of wing fragments might be a clue.

    If this is the case, before going to the expense of a new trap, which seems to have served you well, I'd stay up a bit later one night and empty it then to compare catches. Or, if you leave it until daylight, set the alarm earlier.

    Hope this helps,

    PS: just seen Dave's comment, would be helpful.

  3. Thanks both. Photo now attached.

  4. Hi Alan, that looks exactly the same as my trap with the dual actinics. Yours, though, is in much better nick and with crystal clear perspex which all looks to fit neatly! I think it must be something predating them.

  5. I have one of these traps. In the hope of improving the catch numbers, this year I moved the trap from the middle of the lawn onto a plastic garden table, the idea being to improve its visibility to overflying moths and to baffle the resident frogs which surround it. It hasn't worked even though I defy any ground based predator to climb the legs of the table. The only plausible predators would be birds, of which there are plenty but I am not convinced. I routinely look at the trap before I go to bed and have seen moths in the trap which haven't been there in the morning. I also get very few micros. I think moths just blunder around until they find the opening by accident and fly off.

    Dave Ferguson

  6. Thanks Dave. I was thinking of raising the trap but your experience suggests that wouldn't help. I agree with you, I can't see birds getting in and out of trap.

  7. Hi Alan,

    Thanks for adding the trap picture, helpful in that it shows (in my opinion, anyway!) that you have too much space inside the trap for moths to fly around. Load it up with more egg-boxes so that they're encouraged to settle and have plenty of dark places where they can hide.

    If it is the case that you wait until well after dawn before looking at the trap, then that's another big problem. Not only will the moths be encouraged to fly around looking for somewhere safer to pass the day (and some will eventually find their way out through that slot), but also there's a greater chance of predators finding them especially if they are easily visible through the perspex. I always get up when it is still dark (5am at the moment) to secure the trap and check surrounding vegetation by torchlight because birds are certainly very active in the half-light. I see our garden robins and blackbirds make a bee-line for where the traps were as soon as I'm out of the way (the robins having been "tick-ticking" at me from bushes right from the start even when it is pitch black).

    Birds tend to carry off their prey to somewhere else so you wouldn't necessarily see evidence in the form of wings lying around in quite the same way that you do from bats, but if predators are involved there are usually other signs as well such as bird or rodent poo. Smaller birds (robins, wrens) have been known to enter traps but in my experience that's unusual. If there are no signs inside the trap then that's probably not a problem for you.

    Predators will certainly take any moths on the outside of the trap, of course, and there can often be quite a few such moths on a Skinner. Also, many micros simply congregate on the perspex rather than entering the trap so would fly off when it gets light. Skinner traps are great for micros if you are going to monitor them and can pot up the moths as they arrive, but not quite so good if they are left unattended. I use them regularly when trapping away from home but never do so in the garden.

    So, to sum up, try adding more egg-boxes and get up when it is still dark to secure the trap (a towel or something similar to block that slot and make sure the trap is in a cool, shady spot until you are ready to go through the contents - I bring mine into the garage). If things don't improve then perhaps think about investing in a Robinson style trap which is far better at retaining the catch. If that doesn't help then maybe it is time to move house!!

  8. Hello Alan,
    By trial and error, I have been following the approach that Dave describes for the last few months and it makes a big difference. A couple of practical suggestions:

    As I didn't have a suitable old towel available, I use a scrunched-up length of old bubble-wrap to block the hole between the Perspex sheets. Of course, I remove the light(s) and light bar first.

    When I set up my trap, I place it on an old white sheet. I think it attracts a few moths by reflecting more light, and it makes some of them easier to find when I secure the trap before sunrise. I then use that sheet to wrap up the trap, before I go back to bed.

    Of couse, this is after I've recorded the moths on and outside the trap - potting any that need more time/light to study/photograph later, and dispersing the others around the garden. This does mean that the pre-sunrise activity takes me 45 minutes to an hour to complete (actually, the sun has usually risen before I've finished). However, the robins are serenading me when they aren't tick-ticking; and in conjunction with some pretty sunrises and some interesting moths outside the trap, it means that life at oh-dark-thirty isn't too bad!

  9. Alan - I can't add much to the general advice given above (getting up before dawn, then covering the trap entrances with old towels laid so that they overlap the back edge of the perspex 'sliders' and over the central bar). My trap is a home-made Skinner-type and I use intact egg boxes (without lids of course) - your egg boxes look broken up - and pile them up in an irregular pattern but leaving some clear space centrally so that the moths can access the sides of the boxes. A recent modification to attempt to retain more moths is to stick a strip of plastic along the bottom edge of the perspex sliders so that the plastic hangs vertically down - this makes more of an internal funnel and hopefully impedes the ability of the moths to escape by flying back into the gap between the sliders (I used fairly heavy-duty plastic sellotaped onto the perspex bottom edge) - this also helps close any gap between the perspex and the egg boxes.

  10. Thank you all for your advice, it is very much appreciated.

    I think adding more egg boxes is very good advice. I have let the number dwindle as they have got tatty and fallen apart and that has coincided with the reduced moth numbers. I did move the boxes away from the gap thinking the moths might have been using them to reach the gap in the perspex, but that would have created a larger space for them to take flight.

    I haven't seen any signs of poo in the trap or separate wings so I'm pretty sure predation isn't a major problem in the trap. I have found the odd wing before but I'm pretty sure that was caused by wasps or hornets entering the trap.

    The trap is close to the house against the patio doors and I need to leave a gap for the cables to go through. I have large curtains over the doors which have a white lining and I frequently find several moths on this lining.

    Once again, thanks for all your time and trouble.


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