I often do it on an envelope. Using my saliva as paste through licking the edge of flap. It's the most easy way if you don't have a paste. I also do it on stamps. I don't know any danger that might cause me by doing such thing. I never even thought any possibility that an insect egg might be lurking on them.
Have you heard of a post office worker whose tongue was infested by cockroaches? She noticed a growing lump in her tongue, not knowing the cause of how and why it sprouts suddenly.
By the way, here's the story:
A woman was working in a post office. She was supposed to use a sponge to seal the envelopes but one day she didn't. She used her tongue instead.
Days after, she noticed that her tongue had a strange lump in it. It got so big that she was having a hard time eating or talking. That was when she decided to see a doctor. He cut open the lump and a live roach crawled out! Turns out, there were roach eggs on the envelope flap and they hatched in her tongue!
This urban legend did not actually originated in the Philippines. Someone adapted the story from US, and spread it here. I have no estimate when the story started to arrive in our country, I guess, when it was still a fresh talk of the mouth.
According to the original story, a women working in California post office started to use her tongue instead of a sponge. The same as the above story, she noticed a lump growing in her tongue so she decided to see her doctor to know what was happening on her. After doing some examination, they decided to cut it, and to their surprise, a living cockroach crawled from inside. It was discovered that the insect came from envelop flaps. It made its way to her tongue by her habit of just licking them. It was planted their not knowing it.
The thought of it was very disgusting. Even by just imagining how it crawled out from the cut wound in her tongue. But on the other hand, I don't believe the story. First, I was thinking how it end up inside her tongue. It could be possible that if she has a wound there during her usual licking, the eggs were planted. However, why will she still continue to lick the flaps if she had a wound. Maybe she's not stupid enough to do it knowing the possibility of infection. Second, how did it survive inside a lump? And third, she could have felt something moving there. Well, I haven't experienced such thing, so I am not sure with my own explanation. Besides, people have been using live maggots on their rotten legs if they have diabetes. (Have you heard of it too? It's actually true. NOT an urban legend.)