First make sure that your specimen is no longer alive. To do that, here are two easy recognized methods:
Put the specimen in the freezer (three days minimum) right up until the time you send it.
If you’re sending it by mail, let it air dry for a few days and then place in a container made of hard material. Add cotton batting or tissues to prevent the specimen being damaged against the walls of the container.
This method is recommended for soft-bodied arthropods (spiders, caterpillars, and so on). A waterproof container has to be used, and the specimen completely submerged in the alcohol.