flea
蚤 centers on a small jumping insect: a flea. The meaning is narrow and concrete, with no major abstract extensions.
蚤 combines 虫 (insect) with a top component that may have originally depicted a hand or claw, but the exact historical development is uncertain.
The insect radical 虫 at the bottom suggests a bug, and the top part 叉 looks like a hand with fingers. Imagine a flea jumping between the fingers of a hand.
For ソウ, picture a flea jumping onto a sewing needle: sew -> ソウ, and the flea leaps away.