h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

One of the problems with this type of trap is that it is not efficient. In other words it does not kill all of the wasps that it catches. Because a proportion of the wasps caught escape, they are able to return to their nests and bring back more of their colleagues so encouraging swarming. This is especially true after the trap has caught and killed a few wasps which then form a raft which prevents more wasps from drowning. The result is that you get more wasps coming into the area that you are trying to protect than you originally had in the first place! Ecologically the trap ends up killing far more wasps than it needs to and cosmetically it looks as though it's doing a good job because of course it continues to kill large numbers of wasps. It is far better to get a high efficiency wasp trap which is less likely to put people at risk.