Stopping snails from eating the rodent bait

[Dave Houston]

This from Helen Jonas ...

Hi there all

I carry out sea bird work on East Island (Whangaokena) off East Cape.  The Island is free of animal pests - rat free since 1999.
 
We have been using black tamperproof bait stations with small "contrac" bait blocks which have a wire through the middle and are within the bait stations.  The main purpose of these is to check to see if there has been munching on the bait block to determine if there has been any reinvaision or not....and at the same time kill whoever is munching them.
 
But problem is, there are snails - tonnes of them, the ordinary garden variety - not native ones.  and they seem to have taken a liking to the bait and we are finding that the baits are totally gone by the time we get out to check them.  We only get out to the island 4 to 6 times a year at the most.
 
Has anyone got any suggestions as to what we can use that won't be consumed by snails.  The long term goal is to have Tuatara on this Island...and so a suitable bait and bait station that would not effect them is also required.
 
Cheers Helen

Anybody got any ideas?

[Ben Barr]

Rentokil have a bait that is wrapped in plastic. I'm not sure if the plastic is permeable to odour, or if the the membrane is broken when you slide the metal pin through it. I'm going to be trialling bait take with this bait vs. it's unwrapped equivalent. We also have serious problems with snails eating our bait.
Will let you know.

[Dave Houston]

Unfortunately wrapping bait seems to reduce the attractiveness of the bait to rodents.  See the paper below.  I wonder if you could set the baits in a substrate that snails didn't like - dry sand or a sheet of sand paper?

Airey, A. & O’Connor, C. Consumption and efficacy of rodent baits to Norway rats DOC Science Internal Series, 2003, 148
http://www.doc.govt.nz/upload/documents/science-and-technical/dsis148.pdf

Abstract
A method currently being used by the Department of Conservation to prevent reinvasion of rodent-free offshore islands aims to increase the stability and life of toxic bait by wrapping it in tinfoil or placing it into plastic ziplock bags. A laboratory study was conducted to assess the acceptance of the baits presented in this manner. Wild Norway rats (Rattus norvegicus) were used to assess the consumption of Storm® wax blocks, Talon® 50WB wax blocks, Talon® 50WB wrapped in tinfoil, or Talon® 50WB placed in a plastic ziplock bag. Each rat was offered a choice of toxic bait and non-toxic RS5 pellet baits as a control over four nights. All test baits had low consumption, resulting in very low mortality.

When bait was wrapped in tinfoil or placed in a ziplock plastic bag, its consumption was reduced even further, resulting in no deaths within these treatment groups. These baits and the way they are currently being used appear to be unsuitable for control of Norway rats on offshore islands.

[Bernard Smith]

haven't had to deal with this but would currently love to know how to stop kaka destroying bait stations...

a few gardening tricks spring to mind; rolling the baits firmly in diatomaceous earth could work, or sprinkling it inside the stations around the bait. It does sound like it's a bit of an indiscriminate killer though, impacts on other inverts could be a concern if they go through the station. Any weta graze? I wonder if there's any Helix specific lures...

Another garden deterent is coarse natural fibre rope - too prickly for them to climb over, though whether it's feasible to fit it to your stations or not is another question. If you can fit a wee coil of it inside and it stays dry it maybe worth a trial at least.

A workmate also suggested broken egg shells - maybe better than DE as it should just deter the snails, without non-target effects. You could possibly warm the blocks a little to get it to stick, and it wouldn't take many peoples worth of brunch to have enough for a trial run.

[steve sawyer]

Hi Helen,

We have  the same habitat at Nicks Head as you have at East Is and the same issue with snails scoffing bait.  We use zip locks placed into a tin foil tray inside a novaflo tunnel with 50 g of pestoff pellets in each bag and snail baits also in and around the tray.  We do this quarterly and the baits last well and keep our mice at 2% and rats at nil.  We also use course salt in our tracking tunnels to prevent the snails from eating our peanut butter and papers during our tracking period (Patsy's idea!) and it works well.   I have tried pellets in zip locks around our base too and the rats don't hesitate getting straight into it on the first night, they dont hesitate chewing through everything containing food in the shed either if they get the chance - who did the research!?

Best

Steve