Tarantulas are big, hairy spiders that are often kept as pets. Female tarantulas can live to be 30 years old, while males typically live no more than a year. Tarantulas have few parasites but they can host hawk wasps and nematode worms, which eat them alive. These conditions are unusual in captive-bred tarantulas. Tarantulas can also rupture their abdomens or lose limbs in falls. They can also moult badly, so that the new body emerging from the exoskeleton is misshapen. Wild tarantulas are beneficial to humans and should generally be left alone, but sometimes pet tarantulas have to be euthanized.
Turn your freezer down as low as you can and leave it at that setting for several hours or overnight.
Clear a space for a paper towel in your freezer.
Pick the spider up very gently and carefully in the paper towel.
Place the spider in the freezer.
Leave the spider in the freezer until it is solid. Spiders are not warm-blooded so this is probably painless.
Obtain an insecticide that is effective on spiders. If the insecticides you currently have in your home do not say the are effective on spiders, buy an appropriate insecticide at your grocery or hardware store.
Read the labelling and follow the directions. All insecticides are poisonous and some of them are toxic to mammals as well as insects.
Apply the insecticide. If you can see the spider in its cage, you may choose to spray it directly. If you can only see its burrow in your yard, you may choose to spray into the burrow with a liquid, or sprinkle powder down the burrow and around the exterior.
Do not breathe the fumes and ventilate the area after the spider is dead if you are using a spray inside your home.
Approach the tarantula with an implement such as a shoe in your strong hand.
Strike the spider hard and very fast, crushing its head completely with the first blow.
Repeat if necessary: you should see no tremors in the legs when you are done. Elapsed time between your first blow and your last should be no more than three seconds.
Many varieties of tarantulas raised for pet trade are docile, but some varieties are voracious, aggressive eaters. Tarantulas are venomous, but not dangerously so to humans. When they are disturbed or frightened, they bite and their fangs can be big enough to hurt. They can also "throw" venomous hairs at the threat; these hairs will generally only irritate a human. Keep this in mind if you're attempting to squash a loose tarantula.