Your opponent cannot attack Insect monsters. If this card battled a monster, at the end of the Damage Step: Change that monster to Defense Position.
Rulings
Individual Card FAQs
If "Prickle Fairy" is changed to an Insect-Type monster with "DNA Surgery", your opponent cannot attack.
Netrep Rulings
If “Prickle Fairy” is turned to Insect-Type and there are only face up Insect-Type monsters on the player's field, the opponent may not attack unless the attacker can inherently attack directly.
If a face-down Insect Type is attacked while “Prickle Fairy” is face up and active on the field, Damage Calculation will proceed normally.
EARTH|
Level 4|[ Plant / Effect ]
ATK 300|
DEF 2000