About This Answer
Picking up partway through an answer, Ajahn Dtun explains muditā as taking joy in the happiness and success of other people. If you wish for success in your own working life and see someone else achieve it before you, just be pleased for them. Carry on creating the conditions for your own success, but do not be jealous.
A second question concerns insects found in the house and how loving-kindness practice applies to them. Ajahn Dtun says one can have goodwill towards all beings and wish for them, for example, that they eventually meet with the Dhamma. But once you have caught an animal, it is not good to keep hold of it for long. It is better to release it from the house as quickly as you can. You can extend loving-kindness to it as you let it go or once it has gone.