Below are pictures that Nick Browning of PEST UK took of what is thought to be Solitary Wasp activity in wooden sleepers in a garden. The customer thought that they had wood worm. These types of wasps are different from ‘normal’ wasps as all female wasps lay eggs which hatch into grubs and turn into adults. 
Solitary wasps will nest in cavities or construct burrows in the soil. Although solitary, they tend to nest in groups. The common wasps that are a nuisance and sting are ‘social’ wasps. These nest together and the Queen is the only fertile female and she lays eggs. Without the Queen the wasp colony will die. The worker wasps are sterile females, the males are not present until they are produced with the Queens as the last batch of grubs in late Summer. The males, or Drones, function is to mate with Queens from other nests and then with their function completed they die off in the Winter.
Nick treated the several areas of the wooden sleepers with a residual insecticide (Effect Microtech CS) that will be absorbed by the wasps as they land and kill them. Without food the grubs will also die off. Solitary wasps are much less common than the normal social wasps. This Summer there have not been many wasp nests about so far. It is either that the wasps nests are not there because the Queens that cam out of hibernation did not survive due to the wet (but warm Spring) we had or the nests are not in an advanced state and will become noticeable later on in the Summer and Autumn. The nests that are in bushes and outside have been especially low in number. The wasps that nest outside are usual the German and Wood wasps. The Queens of these sub species hibernate in the ground and many probably perished in the flooding of last Winter.
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