Taking my inspiration from Brian aka Tarvus (link)** I ran a test of an electric fence for a BSFL bin. The larvae have a reputation as escape artists. This is a small scale test of an electric 'fence' to keep them corralled. Two thin strips of aluminum tape are connected to a small 9 volt battery. Any larva that touches both strips at once completes the circuit and receives a non-lethal shock



** Brian's website has been hacked and is temporarily down. His YouTube video of an electric fence on a worm bin is here

Awesome! I had the same idea and I was delighted to see your tests.

Update with the storage tote (58.4cm x 41.3cm x 31.4cm LxWxH) version of the fence:



So far so good. In the 12 days since the fence was energized no larvae have been found outside of the bin as compared to six found in the two previous days. The bin is totally enclosed in a netting bag so I'm fairly confident that no larvae are getting past the fence. Prior to energizing the fence retrieving wandering larvae from the netting 'bag' had become part of the daily routine.

Battery voltage has only dropped from 9.15 to 8.96 VDC so there is no evidence of the high humidity (80%) in the bin causing partial shorting. I had been concerned that this might drain the battery quickly.

I have only been able to observe one larvae attempt to crawl over the fence only to be shocked and drop to the floor of the bin.

Edit to add YouTube link

The battery drain seems to be very minimal which makes sense as the circuit only closes when a larvae touches both strips at the same time:

2012 April 02 : 9.16VDC

2012 April 26 : 8.93VDC

No larvae have got past the fence during this period. Some raise up their upper body seemingly trying to arch over the fence but fall back to the bin bottom.

The electric fence's battery has only dropped 0.43 volts or 4.7% over the past month as shown in the chart below. No larvae have got past the fence during this period.

The performance of the fence has degraded over the last month and a few larvae were able to escape from the bin on six occasions.



I think there are several contributing factors;

1. Material deposited by the flies and larvae on the bin walls and the fence tape may be protecting the larvae from shocks.
2. The foil surface of the conducting tape is delaminating and coming off.
3. The adhesive backing of the tape lifted from the bin wall in a small area.
4. Declining battery voltage reached a level where the larvae can tolerate the shock.

Cleaning of the tape strips in response to item 1 may have contributed to item 2. The conductive aluminum foil is very thin and doesn't stand up well to any abuse. Copper slug tape might be thicker and a better choice. Another possibility is using wire which could be 'welded' to the bin wall with a soldiering iron. In any case replacing the fence while the bin is active will be a challenge

The high humidity (80%+) in the bin may also have contributed to items 2 and 3.

To solve item 4 a small "wall wart" transformer that outputs approximately 9VDC could be used but a battery is preferred because it allows the bin to be easily moved.

Won't it be easier if you exploit the fact that the larvae are photo-phobic?
A fluorescent lamp placed close to the lip of the bin should deter crawl off. We're actually testing this right now, by putting a small fluorescent reading lamp on top of our testing bin, and so far its working quite good (12 hour test so far). The larvae tried to crawl up, and when they come to a certain distance from the light, they just jump back down.

[Edit]
PS: Yes, I'm the same Arkatufus as the on youtube.

I've copied over my response to your question on YouTube below and added links.

"They may be photo-phobic but they will still climb out under full light conditions as the videos show. Plus there is the cost factor of having a light on 24-7.

The fence is not ideal either as the foil tape eventually delaminated creating gaps the larvae could crawl past. I may try again with wire.

There are passive barriers too which break the surface tension of any water on the walls and causing larvae to lose their grip and fall back into the bin."

See these threads by PeteB for information on a couple of types of passive barriers (link) and (link). Velcro strips have also been used.