Hi everybody,
we are using circular pitfall traps (regular yogurt cups) since many years, and unfortunately, sometimes we encounter mice and lizards as by-catch in our samples.
These animals fall in the pitfall traps, are not able to climb out of it and drown...
Researches (e.g. see link attached) and personal reflections resulted in the following possible easy-to-install preventive measures:
1) covering the pitfall traps with a thin, wide-meshed iron grid, so it is too thin to "grab and climb" for invertebrate, but slippery enough for insects and spiders
2) using funnels with a slippery surface, so small vertebrata can't enter, while insects can fall into it
I personally like more solution 1, but I wanted to ask you to share your experience :-)
We aim mostly on spiders, centipedes, millipedes, beetles and other surface insects.
Thank you and greetings,
Michael
https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/444/444-416/444-416_pdf.pdf
I think a metal mesh cylinder surrounding the pitfall has to be very effective and prevents the vertebrates from taking shelter.
Hey Manuel, thank you for your suggestion. We used such metal grids in high alpine soils, as marmots started to dig out the pitfall traps. They work very well!
I was thinking about this, but I am a bit concerned about the diverting of the rest of the soil animals, as they could climb the mesh and therefore not falling into the trap.
I was more thinking about something that keeps small vertebrata on the ground while "walking over the trap" :)
Hi Michael,
I don't think there is a way to solve your problem without biasing the data obtained from the trap catches. If you add a mesh or a funnel, you surely reduce the vertebrate ctaches (but you will never get zero vertebrates as I was told by collegues who have much experience with that kind of traps). But simultaneously, you will also loose many of the larger beetle species (eg Carabus) as they are similarly sized. So your pitfall data will not only underrepresent small species (as pitfall traps always do) but also large species to unknown extent. In my opinion, a risk assessment before placing pitfall traps is better than these methods which may end in biased and potentially misleading data. We should always think about how many pitfall traps we really need and where to place them. Additionally, meshes increase the handling time of each trap (it may just be 20 sec - but the sum is large over a day of field work) and you have to think about practicability. Ending with an anekdote: I once used meshes and ended up with many mice - the weather was very dry and they simply forced themselves through the mesh (which was clearly visible as the mesh-wire was bent) to get to the water inside the cup - so you never know ....
Best, Fabian
Thank you Fabian,
yes, you are right! We have to think about the trade-offs of using a mesh or not :)
I was thinking about a wide-meshed screen placed on the cups, so it is plane to the ground that mice and other small vertebrates should handle to "balance" over the trap, while "clumsy" beetles and arachnids should fall down.
I like to improve techniques, and so maybe I will try something, for example half of traps with mesh and the rest without, just to see if it works.
We use propylene glycol as preserving agent, it is less sweet as ethylene glycol and colorless, so the animals do not lose their coloration (except for Lumbricidae when they swim in it for a longer time).
However, good to know that you and others already made some experience with meshes! In an alpine fragmented pasture at 2800m we used it to prevent marmots digging out our traps (see picture attached).
Greetings,
Michael
I also think that the funnel is a satisfactory solution, but it could encourage the use of the pitfall as a refuge.
Undoubtedly, any solution can modify the results. I think you have a good opportunity to perform a statistical analysis comparing the results obtained in control traps, mesh traps and funnel traps. This would be a nice project :)
Maybe I will start some project ;-)
I also think, it depends on what you are looking for: if you want the activity, then applying no extra mesh or funnel should be the best solution, and you have to deal with possible vertebrata catches.
But if you "just" want to know, which animals live there (so, no real monitoring, only an inquiry), meshes and funnel should work with satisfaction. Probably leaving the pitfall traps for a longer time and make use of the "dig-in-effect" at the beginning!
Thank you for your help :)
Hi, in case someone's research focuses on necrophagous insects, such as Silphidae coleopterans, then small dead mice or turtles etc in the pitfall traps will bring you tons of specimens (I have experienced this personally) ;-).
Yes, indeed, we had this too... 🙈 So that's why I was asking. We had a lot of Silphidae in the pitfall traps and beside the smell, the data were "skewed" 😔
Hello Michael; In collecting ants I use traps similar to yours and have dealt with two problems. 1. Coyotes or raccoons sometimes persistently disturb the traps. I made screen cages similar to the photo above but strong enough to set a rock on. That keeps the pests away. 2. Small vertebrates are protected by putting a stick in the cup that is long enough to protrude above the lip. Lizards and shrews can climb out but ants seem unable to. I have no evidence that these measures bias the ant catch. Good luck, Jim Des Lauriers
Dear James,
thank you for this suggestions. We used nets in some approaches, so beetles could escape, but using sticks could help. What kind of sticks did you use? Wooden sticks or metal sticks? What diameter? :)
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