From Nookipedia, the Animal Crossing wiki
Catching the scorpion
The Scorpion is a harmful insect, meaning that it can cause damage in some way. In this case, if players take out their net or have their net equipped when nearby, it will chase after them, running just as fast. If it stings them, it knocks them out, forcing them to re-appear in front of their house. The only way to avoid getting stung is to enter a building or to catch it. The player will scare any villagers talked to while being chased. The Scorpion can jump off cliffs, jump over small walls (like those of a ramp as it slopes down), and walk over holes.
To catch the Scorpion, players must slowly sneak up on it. Because it is not scared, it will not run away from the player, even if it is staring directly at them. The Scorpion's small size makes it difficult to notice if the player is not paying attention, so the player must stay alert during the time the Scorpion appears. Also, the Scorpion will always appear around the same area, just like the Tarantula.
Donation to the museum
In Wild World
Upon donation of the Scorpion to the museum, Blathers the curator will say the following:
"I've heard that a scorpion can be affected by its own poison, you know. If so, why carry around such dangerous material? Blech! Foolish wretch... If I walked around with a piano above my head, I'd expect to be squashed, wot!"
After donation, the Scorpion can be found on the second tier of the museum, in the same enclosure as the Tarantula. The Scorpion and Tarantula can be seen battling with each other when both have been donated. The Scorpion can be seen shaking its stinger at the Tarantula (once donated), which makes a rattling noise. The Tarantula can be heard making a hissing-type noise in return, which might be associated with the insect's defense mechanism of scratching hairs at enemies. They will circle each other, and eventually, both jump into the air and collide, then begin their battle again. If the Scorpion is donated on its own without the Tarantula, it will be aware of the player's presence and shake its stinger at them instead, but never attacking. If the player has the net equipped when walking in the museum (although it is not visible), sometimes the Scorpion will lunge out of its area and chase the player.
In City Folk
"...Scorpions are assuredly attention getters. They've got those colors that say, "Stay back! I'm poisonous!" However, it seems only a tiny group of scorpions have venom lethal enough to off you with one sting. Mischievous scorpions that look like highly poisonous ones probably fooled folks into thinking otherwise."
In New Leaf
"Scorpions resemble crabs and are in the class arachnida, though they aren't aquatic. Most species possess venom, but of the 1,000 or more species, only 25 are deadly to humans. Scorpion eggs hatch inside the females abdomen, and the young spend time on her back after birth."
Scorpions belong in Arachnida class, which also includes spiders and ticks. Unlike most arachnids, scorpions are ovoviviparous, which means scorpions hatch eggs inside their bodies while their young are born live. Then, the young depend on their mother by riding her until their first molt. Scorpions are found in a variety of landscapes, except for the tundra, in all continents except for Antarctica. Although scorpions are feared generally, only 25 out of over 1700 known species can produce potent enough venom to kill humans. Scorpions are nocturnal, hence why they are found only during the later hours of the day in Animal Crossing. Scorpions are known to consume massive amounts of food in one sitting, and they have low metabolism. Despite this, they can consume only liquids.