bee sting
螫 centers on the sharp, painful puncture of a bee sting. The meaning is specific to the act of a bee injecting venom.
螫 combines 赦 (pardon, release) with 虫 (insect). The exact historical role of 赦 is uncertain; it may have contributed sound or a sense of releasing venom.
The top part 赦 suggests releasing or letting go, and the bottom 虫 is an insect. Imagine a bee releasing its sting into skin.
For セキ, picture a bee sting causing a sudden, sharp 'seki' (like a quick, high-pitched 'seck') sound as it pierces the skin: seki -> セキ.