Regellian blood worm

From Memory Alpha, the free Star Trek reference

You may be looking for the Regulan bloodworm.

Regellian blood worms are organisms known for their size. Presumably, they are leech-like, swelling as they feed from their prey.

When Noah Lessing was ten, he once walked through a patch of poison ivy and swelled up like a Regellian blood worm. (VOY: "Equinox, Part II")