Which predator / prey pair of species have the most drastically different body size?

Question

I'm trying to identify which 2 species, one predator species and one prey species that have the biggest size difference. Specifically, which predator hunts the largest prey relative to itself?

I'm looking for the pair with the smallest predator taking the largest prey but relative to each other, not the other way around.

Some limiting factors to the question:

1. Parasites don't count. Parasites will, ideally, repeatedly feed on the same host for as long as possible. Killing the host will, eventually, remove the resource, which is undesirable for the parasite (it can't keep feeding on the host if the host ceases to exist). I'm looking for a predator prey relationship that does not do this in any way, shape, or form. Even if the predator does not consume the majority of the prey, the portion consumed must be vital to the prey, or the prey must be killed in order to access it or overcome resistance to it.

2. Animals eating plants don't count. Animals eating other animals only please.

3. Pack hunters don't count. Lions, wolves, orcas, army ants, etc., don't count because packs can come in so many shapes and sizes that it makes it impossible to pin down a size ratio between the pack and the prey. Single predator individuals only, please.

4. Scavenging doesn't count. Predators might also scavenge, but prey species used in the size comparison should only include species that the predator actively hunts as part of its regular active hunting routine (even if intermittently or seasonally).

5. Intentional prey sharing doesn't count. Sure, a predator might have it's prey stolen after a kill, that's fine. In many predator species, parents will share kills with offspring until they are capable of hunting for themselves, that's fine too. But nothing like the Tarantula Hawk that doesn't actually eat the "prey" itself, but rather leaves it to be eaten by offspring later. But typical behavior, even in the presence of non-self-reliant offspring, and assuming another predator doesn't take the kill by force, should be for the individual predator that makes the kill to also be the individual that consumes the largest share of the nutritive portions of the prey.

6. Body mass is the primary measurement for "size". Since length, width, height, etc., can vary widely based on body plan, let's use mass as the measurement for "size" for the purposes of this question.

7. Size of the predator should be the mass of a 'typical' or 'average' adult member of the species that performs the actual hunt / kill. For species with significant sexual dimorphism in relation to size between male and female, use the size of whichever sex is generally larger.

8. Size of the prey should be the mass of the 'average' specimen taken in a predation event. For example, Lions (yes, I know I excluded them in the 'pack' section earlier, but for the sake of example), lions will eat elephants. This is most commonly scavenging, rather than hunting. And when it is due to hunting, it's more often calves, not adult elephants, that are taken in the hunt. So (if lions were allowed, and were compared to elephants) the scavenged elephants wouldn't count toward the 'average', only the hunted ones, and the average would be closer to the size of a calf, rather than an adult, due to the higher frequency of predation events involving calves.

9. The ratio matters, not the absolute mass difference. I'm looking for the pair with the biggest ratio, or percentage difference, not the greatest sheer difference in mass. For example, Pair A is a 20 pound predator taking a 30 pound prey, this is only a 3:2 ratio and a 10 pound difference. Pair B is a 1 pound predator that takes a 5 pound prey, which would have a much larger ratio of 5:1 despite only a 4 pound difference. Pair B is the winner here, by ratio.

Given all of this, which two species, that have a predator and prey relationship, have the greatest mass difference between the predator and the prey?

Answer 1

I think the Black Swallower (Chiasmodon niger) is a good contender. This fish can (at least according to Wikipedia and reference therein) can swallow other fish that are up to twice its length and 10x its mass.

For land based predators, the Least Weasel (Mustela nivalis) is capable of killing prey 5-10x its weight, though these instances are believed to be rare (at least rarely observed), though they will take birds like Chickens occasionally too. Diet is normally much smaller - rats, mice etc.

Answer 2

It's quite human thing to draw borders everywhere. It's not even fully settled what species definition is hence so many subcategories can be seen in taxonomy. It's even more volatile when comparing body masses where it is varying greatly by regions. To play the game by borders you set then probably biggest predator-prey ratio is some venomous spider vs some much bigger animal.

You didn't determine that predator have to eat whole thing but it's possible to read out that large prey has to be important role in predators' menu not accidental kill.

In mammal world Wolverine Gulo gulo might be the answer. Tundras' most ferocious predator can weight female 8-12kg male 12-18kg and is known capable of killing adult reindeers female 80-120kg male 160-180kg and even elk (200-700kg) that's weakened in winter. In America wolverine is more scavenging but in Fennoscandia they do more active hunting probably because of less big predators who they can follow and scavenge their kill.